Musculoskeletal FOP

CORRECT ANSWER:

In nutritional rickets, vitamin D deficiency impairs the absorption of calcium and phosphate from the gut. The resulting tendency towards hypocalcaemia triggers a compensatory secondary hyperparathyroidism.

Parathyroid hormone (PTH) acts to normalise serum calcium by increasing bone resorption and reducing renal calcium excretion. Crucially, PTH also increases renal phosphate excretion, leading to hypophosphataemia. The high rate of bone turnover, stimulated by PTH and the underlying disease process, causes a significant increase in the serum activity of alkaline phosphatase (ALP), an enzyme produced by osteoblasts.

This combination of low phosphate, high alkaline phosphatase, and high parathyroid hormone is the classic biochemical profile. Serum calcium may be low or within the normal range due to the compensatory mechanisms.

WRONG ANSWER ANALYSIS:

Option A (Low calcium, low phosphate, low alkaline phosphatase) is incorrect because alkaline phosphatase is characteristically high in rickets due to increased osteoblastic activity.

Option B (High calcium, high phosphate, low alkaline phosphatase) is incorrect as this pattern is the opposite of that seen in nutritional rickets and might suggest vitamin D toxicity.

Option D (Normal calcium, normal phosphate, normal alkaline phosphatase) is incorrect as this describes a normal bone profile, which is inconsistent with a diagnosis of active rickets.

Option E (Low calcium, high phosphate, low parathyroid hormone) is incorrect because the physiological response to hypocalcaemia is an increase, not a decrease, in parathyroid hormone.

CORRECT ANSWER:

The clinical presentation of fever, focal bony tenderness, and a significantly raised CRP strongly suggests acute osteomyelitis, despite a normal initial X-ray.

According to NICE and RCPCH guidance, MRI is the definitive imaging modality in this scenario. It is highly sensitive and specific for detecting the earliest pathological changes of osteomyelitis, primarily bone marrow oedema, which occurs within 1-2 days of infection onset.

Plain radiographs typically do not show bony changes for at least 7-10 days. An MRI with contrast enhancement is crucial as it can accurately delineate the extent of infection, identify any subperiosteal or soft tissue abscesses requiring surgical drainage, and guide antimicrobial therapy, thereby preventing long-term complications such as chronic osteomyelitis or growth plate damage.

WRONG ANSWER ANALYSIS:

Option A (Repeat X-ray in 7-10 days) is incorrect as it would cause a significant and unacceptable delay in diagnosing and treating a serious infection.

Option B (Ultrasound of the knee joint) is inappropriate because the clinical findings of localised femoral pain with a non-swollen, mobile knee joint point away from septic arthritis.

Option C (CT scan of the femur) is less suitable than MRI as it is less sensitive for early marrow changes and exposes the child to significant ionising radiation.

Option D (Ultrasound of the femur) is not the definitive investigation as, while it may identify a subperiosteal collection, it cannot adequately assess for intramedullary bone infection.

CORRECT ANSWER:

C (Blue sclerae). This is a classic physical sign associated with Osteogenesis Imperfecta (OI), particularly Type I. The pathophysiology relates to a defect in the synthesis of Type I collagen, which is the primary structural protein of the sclera, bone, and other connective tissues.

The defective collagen results in a thinned sclera, which allows the underlying choroidal veins to be visible, giving the characteristic blue-grey appearance. While other features of OI, such as dentinogenesis imperfecta or hearing loss, may be present, blue sclerae in the context of multiple fractures are highly suggestive of the condition. Differentiating OI from non-accidental injury (NAI) is a critical safeguarding consideration, and this specific clinical sign points strongly towards an underlying genetic disorder rather than inflicted injury.

WRONG ANSWER ANALYSIS:

Option A (Bruising on the torso) is incorrect as bruising in non-mobile infants, particularly on the torso, abdomen, or ears, is highly suspicious of NAI.

Option B (Retinal haemorrhages) are a significant indicator of abusive head trauma and are not a feature of Osteogenesis Imperfecta.

Option D (A history of a simple fall) is less appropriate because multiple fractures at different healing stages are inconsistent with a single, simple fall, raising suspicion for NAI.

Option E (A spiral fracture of the femur) in a non-ambulant infant is considered a classic sign of NAI, resulting from a torsional or twisting force.

CORRECT ANSWER:

The history of a sudden onset of refusal to bear weight after a minor fall in a toddler is the classic presentation for a "Toddler's Fracture". This is an undisplaced spiral or oblique fracture of the tibial shaft.

The mechanism is typically a low-energy torsional force on the tibia. According to established paediatric orthopaedic practice, the most appropriate initial investigation is a plain X-ray of the tibia and fibula, including both anteroposterior (AP) and lateral views. This modality is readily available, has a low radiation dose, and is highly effective for identifying this type of fracture. Often the fracture line is subtle, and initial radiographs may even appear normal, with follow-up imaging sometimes required to show callus formation.

WRONG ANSWER ANALYSIS:

Option A (Ultrasound of the left hip) is incorrect as ultrasound is the investigation of choice for a suspected hip effusion, but the clinical signs in this case point specifically to the lower leg.

Option B (MRI scan of the left leg) is not a first-line investigation for a simple bony injury and is reserved for cases where there is suspicion of soft tissue injury, osteomyelitis, or if radiographs are inconclusive.

Option C (CT scan of the left leg) is inappropriate as it confers a significantly higher radiation dose and is not required for the diagnosis of a simple toddler's fracture.

Option E (Bone scan) is a sensitive investigation for occult fractures or osteomyelitis but lacks specificity and is not the primary imaging modality for an acute, localised injury.

CORRECT ANSWER:

The classic presentation of an adolescent, particularly if obese, with hip, groin, or knee pain and a limp should raise immediate suspicion of a Slipped Upper Femoral Epiphysis (SUFE). The pain is often referred to the knee via the obturator nerve, which can be a diagnostic pitfall.

Examination revealing reduced internal rotation of the hip is a key clinical sign. According to national guidelines, the most appropriate initial investigation is a plain radiograph of the pelvis, including both an anteroposterior (AP) and a frog-leg lateral view. The AP view is crucial for assessing both hips, as SUFE is bilateral in a significant number of cases at presentation or subsequently. The frog-leg lateral view is the most sensitive radiographic projection for detecting the posterior slippage of the femoral epiphysis relative to the femoral neck, which may be subtle on the AP view alone.

WRONG ANSWER ANALYSIS:

Option A (X-ray of the right knee) is incorrect because the clinical findings point strongly to hip pathology, and imaging the knee will miss the diagnosis of SUFE.

Option C (MRI scan of the right knee) is incorrect as it investigates the wrong joint and is not the appropriate first-line imaging modality for suspected SUFE.

Option D (Ultrasound of the right hip) is incorrect because while it can detect a joint effusion, it cannot adequately assess the bony anatomy to diagnose or grade the epiphyseal slip.

Option E (CT scan of the pelvis) is incorrect as a first-line investigation due to the significant radiation exposure; it is typically reserved for pre-operative planning in complex cases.

CORRECT ANSWER:

The clinical presentation strongly suggests septic arthritis of the hip, a paediatric emergency. According to UK guidelines, the most appropriate initial imaging modality is an ultrasound of the hip.

This investigation is rapid, non-invasive, avoids ionising radiation, and is highly sensitive for detecting a joint effusion. Identifying an effusion is the critical first step, as it confirms the need for urgent ultrasound-guided aspiration for microbiological analysis and subsequent joint washout.

The 'irritable hip' is a common presentation in paediatrics, and ultrasound is key to differentiating transient synovitis from septic arthritis. Early diagnosis and surgical drainage are vital to prevent long-term complications such as avascular necrosis of the femoral head and growth arrest.

WRONG ANSWER ANALYSIS:

Option A (Plain X-ray of the hip) is less appropriate initially as it is often normal in early septic arthritis and is insensitive for detecting a joint effusion, though it can help exclude bony injuries or Perthes disease.

Option B (CT scan of the pelvis) is incorrect because it exposes the child to significant ionising radiation and is less sensitive than ultrasound or MRI for visualising joint fluid and early soft tissue changes.

Option C (MRI scan of the hip) is not the first-line choice as it is time-consuming, requires the child to remain still (often necessitating sedation or general anaesthesia), and can delay definitive treatment.

Option E (Technetium-99m bone scan) is not the primary investigation as it lacks the anatomical detail required and is more useful for localising infection when the clinical signs are non-specific or to identify multifocal osteomyelitis.

CORRECT ANSWER:

UK national guidelines, specifically from the National Institute for Health and Care Excellence (NICE), mandate a selective ultrasound screen for Developmental Dysplasia of the Hip (DDH) in infants with specific risk factors. Breech presentation is a primary risk factor, necessitating further investigation even if the Newborn and Infant Physical Examination (NIPE) is normal.

A normal clinical examination does not exclude the possibility of DDH. The appropriate imaging modality for an infant under 4.5 months is a hip ultrasound, as the femoral head is predominantly cartilaginous and not yet ossified. The optimal timing for this scan is between 4 to 6 weeks of age to allow for the resolution of physiological ligamentous laxity common in newborns, thereby reducing false-positive results.

WRONG ANSWER ANALYSIS:

Option A (Reassure and discharge) is incorrect because the presence of a major risk factor like breech presentation mandates further investigation regardless of a normal clinical examination.

Option C (Refer for pelvic X-ray at 4 months of age) is incorrect as X-rays are not reliable for diagnosing DDH until the femoral heads have ossified, which typically occurs after 4-6 months.

Option D (Advise parents to use double nappies) is incorrect because this is not a recognised screening or treatment method for DDH and has no proven clinical benefit.

Option E (Refer to paediatric orthopaedics) is incorrect as the initial step is imaging; a referral is only warranted if the ultrasound scan is abnormal or if clinical signs of instability are present.

CORRECT ANSWER:

The most likely diagnosis is Osteogenesis Imperfecta (OI). The pathophysiology of this genetic disorder involves a primary defect in the synthesis of type I collagen, most commonly due to mutations in the COL1A1 or COL1A2 genes.

Type I collagen is the principal structural protein in bone, sclerae, and other connective tissues. The defective or insufficient collagen leads to significant bone fragility, resulting in recurrent fractures with minimal trauma. The classic blue sclerae are a direct consequence of this collagen defect, as the sclera becomes abnormally thin and translucent, allowing the underlying choroidal veins to be visible. The family history is consistent with the predominantly autosomal dominant inheritance pattern of OI.

WRONG ANSWER ANALYSIS:

Option A (Non-accidental injury) is less probable because the combination of blue sclerae and a specific family history strongly suggests an underlying genetic disorder.

Option B (Rickets) is incorrect as this disorder of defective bone mineralisation typically causes skeletal deformities like leg bowing and delayed motor milestones, rather than multiple fractures from minor trauma.

Option D (Leukaemia) is incorrect because while it can present with bone pain and pathological fractures, it is not associated with blue sclerae.

Option E (Transient synovitis) is incorrect as it is an acute, self-limiting inflammation of the hip joint causing pain and a limp, and is unrelated to bone fragility.

CORRECT ANSWER:

Rickets is a disease of growing bone, primarily affecting the sites of most rapid growth, such as the wrist. It is caused by defective mineralisation of the osteoid matrix.

This failure of mineralisation is most evident at the physis (growth plate). The zone of provisional calcification is absent, leading to an accumulation of unmineralised osteoid and cartilage. This results in disorganisation and widening of the growth plate.

Radiologically, this appears as a widened, irregular, and frayed physeal line. The metaphysis loses its sharp border, becoming concave or "cupped," and appears wider than the diaphysis, a finding described as metaphyseal splaying or fraying. These changes are the most characteristic radiological signs of active rickets.

WRONG ANSWER ANALYSIS:

Option A (Multiple healing fractures) is incorrect as this finding is more suggestive of non-accidental injury or a primary bone fragility disorder like osteogenesis imperfecta.

Option B (Periosteal reaction) is a non-specific sign of bone irritation and can be seen in trauma, infection, or malignancy, but it is not the classic feature of rickets.

Option D (A transverse fracture of the distal radius) describes a common childhood fracture pattern but is not a pathological feature of active rickets itself, although bones may be weaker.

Option E (Increased bone density (sclerosis)) is incorrect because rickets is characterised by decreased bone mineralisation (osteopenia), the opposite of sclerosis, which is seen in conditions like osteopetrosis.

CORRECT ANSWER:

The diagnosis is nutritional rickets. The pathophysiology stems from Vitamin D deficiency, which is essential for intestinal calcium and phosphate absorption. In its absence, hypocalcaemia develops. This stimulates parathyroid hormone (PTH) secretion, which increases renal calcium reabsorption and phosphate excretion, and mobilises calcium from the bone.

The inadequate mineralisation of the osteoid matrix at the growth plates leads to the characteristic skeletal deformities. Clinical features include delayed motor milestones, such as walking, and bone pain. The classic signs presented here are genu varum (bowed legs) due to weight-bearing on soft long bones, and widening of the wrists, which is a result of metaphyseal fraying and cupping. Exclusive breastfeeding without the recommended vitamin D supplementation is a major risk factor, as breast milk contains insufficient amounts of vitamin D.

WRONG ANSWER ANALYSIS:

Option A (Osteogenesis imperfecta) is less likely as the presentation is not primarily with recurrent fractures, blue sclera, or a relevant family history.

Option B (Blount disease) is incorrect because it is a localised growth disorder of the proximal tibial physis, whereas rickets is a systemic metabolic bone disease affecting multiple sites.

Option D (Non-accidental injury) would typically present with unexplained bruising, fractures of varying ages, or specific fracture patterns, not the symmetrical skeletal changes of a metabolic disorder.

Option E (Cerebral palsy) is incorrect as it is a non-progressive neurological disorder causing motor impairment, but it does not cause the characteristic bony deformities like wrist widening.

CORRECT ANSWER:

The presence of Anti-nuclear antibody (ANA) is the single most important prognostic factor for the development of chronic anterior uveitis in a child with oligoarticular Juvenile Idiopathic Arthritis (JIA).

Uveitis in this context is often asymptomatic in its early stages, making regular ophthalmological screening essential to prevent irreversible visual impairment. National guidelines from bodies such as the British Society for Paediatric and Adolescent Rheumatology (BSPAR) and the Royal College of Ophthalmology recommend the most frequent slit-lamp examinations for children who are ANA-positive, typically every 3-4 months.

This intensive surveillance allows for early detection and timely initiation of treatment, thereby preserving vision. The combination of oligoarticular JIA, female sex, young age at onset, and ANA positivity confers the highest risk.

WRONG ANSWER ANALYSIS:

Option A (Rheumatoid Factor) is incorrect as it is characteristically negative in this subtype of JIA and is associated with polyarticular disease.

Option B (C-reactive protein) is a non-specific marker of inflammation and, while it may be elevated, it does not have the specific prognostic value for uveitis risk that ANA does.

Option D (HLA-B27) is incorrect because it is strongly associated with enthesitis-related arthritis and acute, rather than chronic, anterior uveitis, which typically affects older boys.

Option E (Erythrocyte sedimentation rate) is also a non-specific inflammatory marker and lacks the predictive power of ANA for determining the risk of developing chronic anterior uveitis in JIA.

CORRECT ANSWER:

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by mutations in the gene encoding the protein dystrophin. Dystrophin is essential for maintaining the structural integrity of muscle fibres during contraction.

Its absence leads to continuous cycles of muscle fibre necrosis and regeneration. Over time, the regenerative capacity is exhausted, and muscle tissue is progressively replaced by fibrofatty connective tissue. This process is particularly evident in the gastrocnemius and soleus muscles, resulting in the characteristic calf muscle pseudohypertrophy. While these muscles appear enlarged, they are functionally weak, contributing significantly to the proximal muscle weakness, Gowers' sign, and the typical waddling gait seen in affected boys.

WRONG ANSWER ANALYSIS:

Option A (Spasticity of the lower limbs) is incorrect because spasticity is a sign of an upper motor neurone lesion, whereas DMD is a primary myopathy characterised by progressive weakness and hypotonia.

Option B (Joint hypermobility) is incorrect as this is a feature of inherited connective tissue disorders, such as Ehlers-Danlos syndrome or Marfan syndrome.

Option D (A single swollen knee joint) is incorrect as a monoarthritis is suggestive of an inflammatory condition like Juvenile Idiopathic Arthritis, septic arthritis, or trauma.

Option E (Blue sclerae) is incorrect as this is a classic clinical sign of osteogenesis imperfecta, a genetic disorder affecting type I collagen synthesis.

CORRECT ANSWER:

The diagnosis of oligoarticular Juvenile Idiopathic Arthritis (JIA) is made clinically based on the chronicity of symptoms and specific features. JIA is defined by arthritis lasting for more than six weeks in a child under 16. This boy's 3-week history is progressing towards this timeframe, making acute causes less probable.

The presentation of a single swollen joint (monoarthritis) is characteristic of oligoarticular JIA, the most common subtype. Gelling, or stiffness after periods of inactivity such as a nap, is a classic feature. The absence of fever and normal inflammatory markers (FBC, CRP) helps to exclude infective and systemic inflammatory causes, further supporting a diagnosis of JIA.

WRONG ANSWER ANALYSIS:

Option A (Transient synovitis) is incorrect as it is a self-limiting condition that typically resolves within one to two weeks.

Option B (Septic arthritis) is unlikely due to the child being afebrile and well, with normal inflammatory markers and a non-tender joint.

Option D (Leukaemia) is less likely as, while it can present with limp, one would often expect systemic symptoms or abnormalities on the full blood count.

Option E (Perthes disease) is incorrect because it is an avascular necrosis of the femoral head, presenting with hip pain and a limp, not a swollen knee.

CORRECT ANSWER:

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder. The gene encoding the dystrophin protein is located on the X chromosome.

As males (XY) possess only one X chromosome, a single recessive mutation on this chromosome will result in the clinical phenotype. Females (XX) are typically asymptomatic carriers because the presence of a normal dystrophin gene on their second X chromosome provides adequate protein function, although some may exhibit mild symptoms such as cardiomyopathy.

The condition is inherited from a carrier mother, with each male offspring having a 50% probability of being affected and each female offspring having a 50% chance of being a carrier.

WRONG ANSWER ANALYSIS:

Option A (Autosomal dominant) is incorrect as this inheritance pattern, seen in conditions like Marfan syndrome, affects both sexes and only requires one mutated allele to manifest.

Option B (Autosomal recessive) is incorrect because this pattern, characteristic of Spinal Muscular Atrophy, requires two copies of the mutated gene, with parents typically being unaffected carriers.

Option D (Mitochondrial) is incorrect as this inheritance is passed exclusively from the mother to all her children via mitochondrial DNA, a pattern not seen in DMD.

Option E (X-linked dominant) is incorrect because in this mode, an affected father would transmit the condition to all his daughters, which is not the inheritance pattern of Duchenne muscular dystrophy.

CORRECT ANSWER:

The clinical presentation of a chronic monoarthritis lasting four weeks, accompanied by morning stiffness and the absence of fever or systemic upset, is highly indicative of oligoarticular Juvenile Idiopathic Arthritis (JIA).

According to NICE guidelines, children with suspected JIA require specialist assessment. A referral to a paediatric rheumatologist is the crucial next step to confirm the diagnosis, initiate appropriate investigations (including for complications like uveitis), and commence disease-modifying anti-rheumatic drugs (DMARDs) if necessary. Early specialist management is vital to prevent long-term joint damage and disability. The pathophysiology involves an autoimmune-mediated inflammation of the synovial membrane, leading to joint swelling, pain, and stiffness.

WRONG ANSWER ANALYSIS:

Option A (Admit for IV antibiotics) is incorrect as septic arthritis is an acute condition characterised by high fever, severe pain, and a systemically unwell child.

Option B (Refer urgently to orthopaedics) is inappropriate because joint aspiration is primarily for suspected septic arthritis, which is not suggested by this chronic, afebrile presentation.

Option C (Reassure and manage with ibuprofen) is incorrect because transient synovitis is a self-limiting diagnosis of exclusion that typically resolves within one to two weeks.

Option E (Apply an above-knee cast) is inappropriate as a Toddler's fracture presents as an acute injury with an unwillingness to bear weight, not a four-week history of joint swelling.

CORRECT ANSWER:

The manoeuvre described, where a child rises from the floor by rolling prone and using their hands to climb up their own legs, is the classical description of Gower's sign. This sign is a pathognomonic feature of significant proximal muscle weakness, specifically affecting the pelvic girdle and lower limb muscles.

The underlying pathophysiology involves weakness of the hip and knee extensors (gluteus maximus and quadriceps). This prevents the child from extending their trunk and lifting their body from a squatting position without support. Instead, they must use their arms to push their body upright, compensating for the lack of power in their proximal leg muscles. It is most famously associated with Duchenne muscular dystrophy, a dystrophinopathy.

WRONG ANSWER ANALYSIS:

Option A (Trendelenburg sign) is incorrect as it describes a pelvic tilt when standing on one leg, indicating weakness of the contralateral hip abductors.

Option C (Ortolani manoeuvre) is incorrect because it is a specific test used in neonates to confirm the relocation of a dislocated hip, not a sign of muscle weakness in a 5-year-old.

Option D (Barlow manoeuvre) is incorrect as it is a neonatal examination technique used to identify a hip that can be dislocated.

Option E (Romberg's test) is incorrect because it is an assessment of balance and proprioception, where the patient stands with feet together and eyes closed, and is not related to rising from the floor.

CORRECT ANSWER:

Children with oligoarticular juvenile idiopathic arthritis (JIA), particularly those who are antinuclear antibody (ANA) positive, are at the highest risk of developing chronic anterior uveitis. This inflammation of the eye is often asymptomatic in its early stages, meaning a child will not complain of pain or visual disturbance until significant, and often irreversible, damage has occurred.

Untreated uveitis can lead to severe long-term complications including cataracts, glaucoma, and permanent visual loss. UK guidelines from the Royal College of Paediatrics and Child Health (RCPCH) and the British Society for Paediatric and Adolescent Rheumatology (BSPAR) mandate a strict screening protocol with regular slit-lamp examinations by a paediatric ophthalmologist. The frequency of these screenings is determined by the JIA subtype, ANA status, and age at onset, but it is the most critical intervention to prevent sight-threatening disability in this patient.

WRONG ANSWER ANALYSIS:

Option A (Paediatric cardiology for echocardiogram) is incorrect because pericarditis and other cardiac complications are primarily associated with Systemic JIA, not the oligoarticular subtype.

Option C (Paediatric nephrology for renal ultrasound) is incorrect as significant renal disease, such as secondary amyloidosis, is a very rare and late complication of chronic, poorly controlled inflammation, not a target for initial screening.

Option D (Paediatric orthopaedics for hand X-rays) is incorrect because radiological investigation would be focused on the clinically affected joint (the knee), and routine screening of uninvolved joints is not indicated.

Option E (Audiology for hearing assessment) is incorrect as there is no direct association between oligoarticular JIA and hearing impairment that would necessitate routine audiological screening.

CORRECT ANSWER:

B: Serum creatine kinase (CK). The pathophysiology of Duchenne muscular dystrophy (DMD) involves a mutation in the dystrophin gene, leading to the absence of the dystrophin protein. This protein is crucial for maintaining muscle fibre integrity.

Without it, muscle cells undergo progressive necrosis and are replaced by fat and fibrous tissue, causing the characteristic clinical signs. This process of muscle breakdown releases intracellular enzymes into the circulation. Serum creatine kinase, a muscle enzyme, is therefore massively elevated, often 20 to 100 times the upper limit of normal. National guidelines recommend checking the CK level as the essential first-line investigation in any boy with signs suggestive of DMD, as it is the most sensitive and specific initial blood test to support the diagnosis before proceeding to genetic testing.

WRONG ANSWER ANALYSIS:

Option A (Full blood count) is incorrect as it assesses for anaemia or infection, which are not primary features of this genetic myopathy.

Option C (C-reactive protein) is incorrect because it is a non-specific marker of inflammation and is not characteristically raised in Duchenne muscular dystrophy.

Option D (Anti-nuclear antibody) is incorrect as it is a screening test for autoimmune disorders like juvenile dermatomyositis, which presents differently.

Option E (Thyroid function tests) would be considered in cases of myopathy, but the specific clinical triad presented is classic for DMD, making CK the priority.

CORRECT ANSWER:

Oligoarticular juvenile idiopathic arthritis (JIA) is the most fitting diagnosis. The history aligns perfectly with the diagnostic criteria for JIA, which requires arthritis for six weeks or more in a child under 16. This girl's symptoms have persisted for six weeks.

The presentation of morning and post-rest stiffness, which improves with activity, is a hallmark of inflammatory arthritis. Oligoarticular JIA is the most common subtype, defined by arthritis affecting four or fewer joints in the first six months of the disease. The examination finding of a swollen, warm, but non-tender right knee is characteristic of the synovitis seen in JIA. The absence of fever and systemic symptoms makes other serious differentials less probable. Early recognition and referral to paediatric rheumatology are crucial as untreated JIA can lead to long-term joint damage and is associated with asymptomatic uveitis.

WRONG ANSWER ANALYSIS:

Option A (Transient synovitis) is incorrect because it is an acute, self-limiting condition that typically resolves within one to two weeks, unlike this child's six-week history.

Option B (Septic arthritis) is less likely as the child is afebrile and the joint is non-tender; septic arthritis is a medical emergency presenting with high fever, severe joint pain, and reluctance to move the limb.

Option D (Perthes disease) is incorrect as it is an avascular necrosis of the femoral head, which would present with hip pain and a restricted range of motion, not a swollen knee.

Option E (Leukaemia) is a critical differential for a limp, but it is less likely here given the prolonged history of a single swollen joint without systemic features like fever, weight loss, or bruising.

CORRECT ANSWER:

This boy presents with the classic triad for Duchenne muscular dystrophy (DMD): progressive proximal muscle weakness, calf pseudohypertrophy, and Gower's sign.

DMD is an X-linked recessive disorder caused by a mutation in the dystrophin gene, leading to an absence or near-absence of the dystrophin protein. Dystrophin is crucial for muscle fibre stability; its absence results in progressive muscle damage and replacement by fibrofatty tissue.

This process explains the characteristic calf pseudohypertrophy (firm, enlarged muscles with reduced function) and the profound proximal weakness, which manifests as Gower's sign – using hands to climb up one's own body from a seated position to compensate for weak pelvic girdle muscles. The presentation at age four with delayed motor milestones is typical.

WRONG ANSWER ANALYSIS:

Option A (Cerebral palsy) is incorrect as it is a non-progressive upper motor neurone disorder, typically associated with spasticity or dyskinesia rather than the progressive proximal weakness and specific signs seen here.

Option B (Becker muscular dystrophy) is incorrect because it presents later, typically in late childhood or adolescence, with a much milder clinical course due to the presence of some partially functional dystrophin.

Option D (Spinal muscular atrophy Type 2) is incorrect as it usually presents before 18 months with progressive symmetrical weakness, poor head control, and tongue fasciculations, and lacks calf pseudohypertrophy.

Option E (Oligoarticular JIA) is incorrect as it is an inflammatory arthritis causing joint pain, swelling, and stiffness, not a primary muscle pathology.

CORRECT ANSWER:

The presence of significant callus formation on the X-ray is objective evidence that the femur fracture is healing. In an infant, radiological signs of healing, such as callus, are typically not visible until at least 7 to 10 days after the injury.

The history provided by the parents of a sudden event "this morning" is therefore fundamentally inconsistent with the radiological findings. This discrepancy is the most important conclusion as it is highly suggestive of a non-accidental injury and a delayed presentation.

According to RCPCH and national safeguarding guidelines, such a mismatch between the reported history and the clinical or radiological findings mandates an immediate child protection assessment. The priority is not the orthopaedic management of a healing fracture, but the safety and welfare of the child.

WRONG ANSWER ANALYSIS:

Option A (The fracture is pathological due to rickets) is incorrect as there are no other radiological features described, such as metaphyseal fraying or osteopenia, to suggest rickets.

Option C (The fracture is consistent with a birth injury) is incorrect because a fracture from birth would be three months old and would show advanced remodelling, not early callus formation.

Option D (The callus formation suggests a healing infection) is incorrect as callus is a normal physiological response to fracture healing, not a specific sign of osteomyelitis.

Option E (The child needs urgent orthopaedic reduction) is incorrect because the presence of significant callus indicates the fracture is already splinted by new bone and is past the acute phase requiring immediate reduction.

CORRECT ANSWER:

The clinical scenario describes a classic torus, or buckle, fracture. This injury is unique to the paediatric skeleton and occurs when a longitudinal compression force is applied to a long bone, typically the distal radius after a fall onto an outstretched hand.

The force impacts the metaphysis, where the bone is more porous and metabolically active. Instead of a complete fracture line propagating through the cortex, the bone fails under compression, causing one or more of the cortical surfaces to buckle or wrinkle. This is an incomplete and inherently stable fracture pattern because the periosteum, which is thicker and stronger in children, typically remains intact, preventing significant displacement.

WRONG ANSWER ANALYSIS:

Option A (Greenstick fracture) is incorrect as it is a tension-related injury where one side of the cortex breaks while the other side only bends.

Option B (Plastic deformation) is incorrect because it describes a bowing of the bone without any visible cortical disruption or fracture line.

Option D (Salter-Harris Type I) is incorrect as this fracture type involves a shear force causing a transverse fracture directly through the growth plate (physis).

Option E (Pathological fracture) is incorrect because the mechanism described is typical for accidental trauma in a healthy child, with no information suggesting underlying bone disease.

CORRECT ANSWER:

This clinical scenario presents multiple significant indicators for suspected non-accidental injury, mandating a safeguarding referral as the immediate priority. National Institute for Health and Care Excellence (NICE) and Royal College of Paediatrics and Child Health (RCPCH) guidelines are unequivocal in such cases.

A spiral fracture of the humerus in a non-ambulant infant is highly specific for inflicted injury, resulting from a torsional force. The provided history of a 3-year-old sibling causing the injury is not developmentally plausible given the force required. Furthermore, bruising on the torso of a 4-month-old is a major red flag, as this is a protected area not typically subject to accidental bruising. Therefore, immediate referral to children's social services and arranging a skeletal survey to identify other occult fractures are essential next steps to ensure the child's safety and investigate potential abuse.

WRONG ANSWER ANALYSIS:

Option A (Accept the history as plausible) is incorrect as the mechanism described is inconsistent with the severe nature of the spiral fracture and the presence of other injuries.

Option C (Place the arm in a sling and discharge) is incorrect because discharging a child with clear safeguarding concerns would breach duty of care and place them at high risk of further harm.

Option D (Ask the 3-year-old sibling what happened) is incorrect as a young child is not a reliable historian, and this action inappropriately shifts the focus from the immediate medical and safeguarding needs of the infant.

Option E (Swab for bone infection) is incorrect because the presentation is clearly traumatic, and there are no signs such as fever or inflammation to suggest osteomyelitis is the primary diagnosis.

CORRECT ANSWER:

This fracture is classified as a Salter-Harris Type III. The defining characteristic of this injury is a fracture line that runs from the articular surface, through the epiphysis, and then horizontally across the physis, without involving the metaphysis.

This is an intra-articular fracture, meaning it disrupts the joint surface, which necessitates accurate anatomical reduction to minimise the risk of future degenerative arthritis. The fracture splits the epiphysis, and because the physis is involved, there is a risk of growth disturbance, although this is less than in Type IV or V injuries. The mnemonic SALTR can be helpful: Type III corresponds to 'L' for 'Lower' or 'BeLow', as the fracture line is below the physis in the epiphysis.

WRONG ANSWER ANALYSIS:

Option A (Salter-Harris Type I) is incorrect because it describes a fracture that runs straight across the physis only, without involving the epiphysis or metaphysis.

Option B (Salter-Harris Type II) is incorrect as this, the most common type, involves a fracture across the physis and then out through the metaphysis.

Option D (Salter-Harris Type IV) is incorrect because it describes a vertical fracture line extending from the articular surface through the epiphysis, physis, and metaphysis.

Option E (Salter-Harris Type V) is incorrect as this is a rare compression or crush injury to the physis itself, which is often diagnosed retrospectively following growth arrest.

CORRECT ANSWER:

In cases of suspected physical abuse in a child under two years of age, national guidelines from both NICE and the Royal College of Paediatrics and Child Health (RCPCH) mandate a full skeletal survey.

This series of specific radiographs is the gold-standard investigation for identifying occult fractures, which are frequently present in such cases and may not have any external signs. It is particularly sensitive for detecting injuries with high specificity for abuse, such as classic metaphyseal lesions and posterior rib fractures, which are often asymptomatic.

While other investigations are also vital, the skeletal survey is the most appropriate and comprehensive initial screening tool for bony injuries throughout the body in this clinical scenario.

WRONG ANSWER ANALYSIS:

Option A (CT scan of the head) is essential to exclude an associated intracranial injury, a common finding in abusive head trauma, but it does not screen for fractures in the limbs and trunk.

Option B (MRI scan of the whole body) is not the recommended primary screening tool for fractures in non-accidental injury as it is less sensitive for key bony injuries and more resource-intensive than a skeletal survey.

Option D (Bone densitometry (DEXA) scan) is incorrect as it is a functional test that assesses bone mineral density and is not a method for detecting acute fractures.

Option E (Serum vitamin D and calcium) is incorrect as these biochemical tests investigate for underlying metabolic bone disease like rickets, but they do not screen for existing traumatic injuries.

CORRECT ANSWER:

Posterior rib fractures are considered pathognomonic for non-accidental injury in infants. The mechanism required to cause these fractures involves vigorous anteroposterior thoracic compression, with the vertebral bodies acting as a fulcrum.

This squeezing action is highly specific to inflicted injury as such forces are not generated during normal handling, falls, or even cardiopulmonary resuscitation. The presence of posterior rib fractures, especially when multiple and in different stages of healing, should raise immediate safeguarding concerns. Their high specificity is a key concept for any paediatrician involved in child protection assessments and is frequently tested in the MRCPCH examination. According to national guidelines, such findings mandate a thorough investigation for other injuries and referral to social care.

WRONG ANSWER ANALYSIS:

Option A (Transverse fracture of the femur) is incorrect because, while highly suspicious in a non-ambulant infant, it is not as specific as posterior rib fractures.

Option B (Linear skull fracture) is incorrect as it can commonly result from accidental trauma, such as a simple fall from a low height.

Option C (Clavicle fracture) is incorrect because it is a frequent and often unavoidable injury sustained during the birthing process or from minor accidental trauma.

Option E (Buckle fracture of the distal radius) is incorrect as this is a very common accidental injury, typically seen in older children after a fall onto an outstretched hand.

CORRECT ANSWER:

The physis contains chondrocytes responsible for longitudinal bone growth. A fracture traversing the growth plate, particularly Salter-Harris types III, IV, and V, can damage these cells and disrupt their blood supply.

This injury can trigger the formation of a 'bony bar' across the physis, tethering the epiphysis to the metaphysis. This leads to premature cessation of growth, known as physeal arrest. Depending on the location of the bar, this can result in either a progressive angular deformity or a significant limb length discrepancy, making it the most crucial long-term complication. The risk is highest in fractures with greater initial displacement and in certain anatomical locations like the distal femur.

WRONG ANSWER ANALYSIS:

Option A (Non-union of the fracture) is incorrect because the rich vascular supply to the metaphysis and epiphysis in children means these fractures almost always heal readily.

Option B (Joint instability) is less significant; while intra-articular fractures (Types III and IV) can affect joint congruity, growth arrest remains the more common and functionally limiting long-term problem.

Option D (Avascular necrosis) is incorrect as it is a relatively uncommon complication, typically associated with specific sites like the proximal femur, whereas growth arrest is a risk in all physeal injuries.

Option E (Chronic pain syndrome) is not the most significant complication, as although possible after any trauma, it is not a specific pathophysiological consequence of the physeal injury itself.

CORRECT ANSWER:

The most critical finding is the presence of multiple fractures at different stages of healing (new, healing, and old). This indicates injuries inflicted over a period of time, which is the classic presentation of non-accidental injury (NAI).

Furthermore, posterior rib fractures are highly specific for inflicted trauma, typically caused by forceful squeezing of the chest. A femur fracture in a non-ambulant infant is also strongly suggestive of NAI. While other conditions can cause bone fragility, this particular combination and timeline of injuries makes NAI the most probable diagnosis. According to RCPCH and NICE guidance, any suspicion of NAI necessitates an immediate and thorough safeguarding investigation.

WRONG ANSWER ANALYSIS:

Option A (Osteogenesis imperfecta Type I) is less likely because while it causes fractures, the specific pattern of posterior rib fractures and injuries at various healing stages is more characteristic of NAI.

Option C (Scurvy) is incorrect as it is exceptionally rare in this age group and typically presents with subperiosteal haemorrhages rather than this traumatic fracture pattern.

Option D (Rickets) is not the best fit because it causes bone softening leading to metaphyseal fractures, not typically the pattern of posterior rib and femoral shaft fractures seen here.

Option E (Caffey disease) is incorrect as it involves cortical hyperostosis, usually affecting the mandible and clavicles, and does not present as multiple fractures in different stages of healing.

CORRECT ANSWER:

A greenstick fracture is an incomplete fracture, common in children, where the bone is angulated with a break in the cortex on the convex side, while the concave side cortex remains intact but buckled.

In a significantly angulated forearm fracture, this angulation must be corrected to prevent permanent malunion, which would result in a cosmetic deformity and, more importantly, a functional deficit with loss of pronation and supination.

The key management principle is to perform a closed reduction. To achieve this, the intact cortex on the concave side must be broken by applying gentle, firm pressure. This manoeuvre, known as completing the fracture, allows the bone to be fully straightened and anatomically aligned. Following a successful closed reduction, the forearm is immobilised in a well-moulded cast to maintain the position for healing.

WRONG ANSWER ANALYSIS:

Option A (Application of a simple splint) is incorrect because a splint alone is insufficient to correct the significant angulation, leading to healing in a deformed position (malunion).

Option C (Surgical fixation with an intramedullary nail) is incorrect as it represents an overly invasive approach for a fracture that can almost always be managed successfully with non-operative closed reduction and casting.

Option D (Immediate referral for physiotherapy) is incorrect because physiotherapy is for rehabilitation after the fracture has been reduced and immobilised, not for the primary correction of a bony deformity.

Option E (Prescribing a 6-week course of analgesia) is incorrect because while pain relief is important, it is purely symptomatic treatment and does not address the underlying need to correct the anatomical alignment of the fracture.

CORRECT ANSWER:

A torus, or buckle, fracture is an impaction injury to the metaphysis of a growing bone, causing the cortex to buckle without a visible fracture line through the opposite cortex.

It is an inherently stable fracture pattern with a very low risk of complications. Current UK practice, informed by major trials like the FORCE trial, supports minimal intervention. The priority is symptomatic control. A removable splint or backslab provides adequate immobilisation to relieve pain while allowing for easy removal for hygiene and comfort.

This approach avoids the complications of a rigid cast and negates the need for a routine fracture clinic follow-up, which is more convenient for the family and cost-effective for the health service. The FORCE trial found that a soft bandage was equivalent to rigid immobilisation for pain control and function.

WRONG ANSWER ANALYSIS:

Option A (Surgical fixation with K-wires) is incorrect as this is reserved for unstable, significantly displaced, or angulated fractures, not stable buckle injuries.

Option B (Closed reduction under general anaesthesia) is incorrect because buckle fractures are not displaced or angulated, thus they do not require manipulation or realignment.

Option C (Above-elbow plaster cast) is incorrect as it provides excessive immobilisation for a stable, distal wrist fracture, causing unnecessary discomfort and joint stiffness.

Option E (Reassurance and analgesia only) is incorrect because while analgesia is essential, some form of immobilisation is standard practice to provide comfort, pain relief, and protection during healing.

CORRECT ANSWER:

The clinical presentation describes a classic Toddler's fracture. This is an undisplaced or minimally displaced spiral or oblique fracture of the distal tibia, occurring in young, ambulatory children, typically between 9 months and 3 years of age.

The mechanism is usually a low-energy torsional force, such as a simple trip or fall while twisting. The child presents with an acute refusal to bear weight on the affected limb. Given the consistent history and the specific radiological findings in this age group, a Toddler's fracture is the most probable diagnosis. While safeguarding should always be considered in a non-verbal child, this specific injury pattern is very often accidental.

WRONG ANSWER ANALYSIS:

Option A (Non-accidental injury) is less likely because the described history is consistent with the injury, and this specific fracture pattern is a well-recognised accidental injury in this age group.

Option B (Pathological fracture secondary to rickets) is incorrect as there are no other signs of rickets described, and such fractures are typically transverse rather than spiral.

Option D (Salter-Harris Type I fracture) is incorrect as this involves a fracture through the physis (growth plate), not a spiral fracture of the tibial shaft.

Option E (Acute osteomyelitis) is less likely as the presentation is not typically associated with trauma and would usually be accompanied by systemic signs such as fever and raised inflammatory markers.

CORRECT ANSWER:

The key to this question is the developmental stage of the child. A 4-month-old infant is non-mobile and lacks the ability to generate the significant torsional force required to cause a spiral fracture of the femur.

Such an injury in a non-ambulant child is highly indicative of non-accidental injury (NAI) unless there is a credible history of major trauma or evidence of a bone disorder. National Institute for Health and Care Excellence (NICE) guidance mandates suspicion of child maltreatment when a child presents with a fracture in the absence of a suitable explanation or a predisposing medical condition.

In contrast, a 4-year-old is mobile and could sustain such a fracture accidentally, for example, from a fall from height during play, making the injury pattern plausible, although it would still warrant a thorough safeguarding assessment.

WRONG ANSWER ANALYSIS:

Option A (The 4-year-old, as their bones are stronger) is incorrect because fracture suspicion in paediatrics is primarily related to the mechanism of injury relative to developmental stage, not bone strength.

Option C (Both are equally suspicious) is incorrect as the likelihood of NAI is significantly higher in the non-mobile infant compared to the preschool child for this specific injury.

Option D (Neither, as spiral fractures are usually accidental) is incorrect because while they can be accidental in mobile children, a spiral fracture in a non-mobile infant is a classic red flag for abuse.

Option E (The 4-year-old, as they are more likely to be mobile) is incorrect because their mobility provides a potential mechanism for accidental injury, which is absent in the 4-month-old, thereby making the infant's presentation more suspicious.

CORRECT ANSWER:

A femur fracture in a non-ambulatory infant is highly indicative of non-accidental injury (NAI). The femur is the strongest bone, and a significant force is required to fracture it.

In a 6-month-old, accidental causes are rare and would typically involve major trauma, which is inconsistent with the vague history provided. National Institute for Health and Care Excellence (NICE) and Royal College of Paediatrics and Child Health (RCPCH) guidelines mandate that NAI must be considered in all children with femoral fractures, especially those who are not yet walking.

Therefore, the immediate priority, after orthopaedic stabilisation, is to initiate safeguarding procedures to ensure the child's safety. A skeletal survey is a crucial part of this investigation to identify other occult fractures, which are common in cases of physical abuse.

WRONG ANSWER ANALYSIS:

Option A (Discharge with close GP follow-up) is incorrect as it would place the child at significant risk of further harm by ignoring compelling evidence of potential abuse.

Option B (Refer to paediatric physiotherapy) is inappropriate as the immediate priority is safeguarding; physiotherapy is a component of later management, not the primary next step.

Option D (Prescribe calcium and vitamin D supplements) is incorrect because the clinical picture does not suggest a metabolic bone disease, and investigating this would delay essential child protection measures.

Option E (Reassure parents that falls are common) is incorrect and negligent, as this type of fracture is not consistent with a simple fall in a non-mobile infant and the inconsistent history is a major red flag.

CORRECT ANSWER:

The Salter-Harris classification system is used to describe fractures that involve the epiphyseal plate or physis (growth plate) in a growing bone. This case describes a fracture line passing across the physis and exiting through the metaphysis, which is the classic definition of a Salter-Harris Type II fracture.

This is the most common type of physeal injury, accounting for approximately 75% of cases. The mnemonic SALTER can be helpful: S (Straight across - Type I), A (Above - Type II), L (Lower or Below - Type III), T (Through or Two - Type IV), ER (Erasure or Crush - Type V). In this scenario, the fracture goes Along the physis and Above into the metaphysis. The metaphyseal fragment is sometimes referred to as the Thurston-Holland fragment.

WRONG ANSWER ANALYSIS:

Option A (Type I) is incorrect because the fracture is not confined solely to the physis; it extends into the metaphysis as described in the vignette.

Option C (Type III) is incorrect as this describes an intra-articular fracture where the line runs from the physis down through the epiphysis into the joint space.

Option D (Type IV) is incorrect because this fracture pattern involves a vertical line passing through the metaphysis, physis, and epiphysis.

Option E (Type V) is incorrect as this is a rare, severe crush injury to the physis, which is not consistent with the described fracture line.

CORRECT ANSWER:

The diagnosis is a Salter-Harris Type I fracture of the distal fibula. This fracture pattern involves a separation directly through the physis (growth plate).

The physis is composed of radiolucent cartilage, meaning it does not show up on an X-ray. Therefore, in the absence of displacement, the X-ray is typically normal. The diagnosis is made clinically based on the history of trauma and the presence of exquisite point tenderness localised directly over the physis. The mechanism of a twisting injury is classic for this type of fracture. Management involves immobilisation, as it is treated as a fracture to prevent premature growth arrest.

WRONG ANSWER ANALYSIS:

Option A (Ankle sprain) is incorrect because the tenderness would be located over the ankle ligaments, such as the anterior talofibular ligament, rather than directly over the bone of the physis.

Option C (Salter-Harris Type II fracture) is less likely as this fracture extends through the physis and metaphysis, and the metaphyseal component is almost always visible on an X-ray.

Option D (Tarsal coalition) is incorrect as it is a congenital condition causing chronic, insidious foot pain and stiffness, not acute pain following a specific injury.

Option E (Achilles tendonitis) is incorrect because it would present with pain and tenderness localised to the Achilles tendon insertion on the calcaneus, not the distal fibula.

CORRECT ANSWER:

B (Non-accidental injury). Multiple posterior rib fractures are considered pathognomonic for non-accidental injury in infants.

The mechanism is forceful squeezing of the chest, causing the rib to be levered against the transverse vertebral process and fracture at its weakest point. This requires a degree of force not encountered in normal handling or even minor accidental trauma.

The finding of fractures at different stages of healing indicates repeated episodes of injury over time, which is a critical feature of abuse. In the context of a well infant with no history of major trauma, safeguarding procedures must be initiated immediately as per RCPCH guidance. This finding is a classic sentinel injury that, if missed, can lead to further harm.

WRONG ANSWER ANALYSIS:

Option A (Severe coughing) is incorrect because fractures from coughing are typically anterior and are very rare in infants.

Option C (Osteogenesis imperfecta) is an unlikely cause without other features such as blue sclerae, joint hypermobility, or a relevant family history, and is significantly rarer than NAI.

Option D (Congenital rib abnormalities) is incorrect as these are structural anomalies present from birth and would not show features of acute fractures or healing calluses on a radiograph.

Option E (Cardiopulmonary resuscitation) is incorrect because CPR-related fractures are almost always anterior or antero-lateral and there would be a clear history of a resuscitation event.

CORRECT ANSWER:

A classical metaphyseal lesion (CML), also known as a 'bucket-handle' or 'corner' fracture, is considered pathognomonic for non-accidental injury (NAI).

The pathophysiology involves a violent shearing or torsional force applied to the limb, such as from shaking or pulling. This force causes the fragile, newly formed bone of the primary spongiosa in the metaphysis to fracture and separate from the cartilaginous physis. Such an injury mechanism is not consistent with accidental trauma or normal infant handling.

The presence of a CML in an infant who is not yet mobile is highly specific for inflicted injury and necessitates immediate safeguarding procedures and further investigation for other injuries.

WRONG ANSWER ANALYSIS:

Option A (Scurvy) is incorrect because while scurvy can cause painful limbs and subperiosteal haemorrhages, it does not typically cause this specific metaphyseal fracture pattern.

Option B (A normal developmental variant) is incorrect as a bucket-handle fracture is a true traumatic injury and is never a normal finding at any stage of development.

Option D (Underlying rickets) is incorrect because rickets leads to defective bone mineralisation, causing metaphyseal fraying, splaying, and cupping, not the distinct shearing fracture seen here.

Option E (A common birth-related injury) is incorrect as birth-related fractures most commonly affect the clavicle or long bone diaphysis, and a metaphyseal fracture would be exceptionally rare and present neonatally.

CORRECT ANSWER:

The most important consideration is safeguarding. A spiral fracture of the femur is a high-energy injury caused by a significant twisting force. A 4-month-old infant is non-mobile and a fall from a sofa is a low-energy mechanism, making the history provided highly inconsistent with the injury sustained.

This discrepancy is a major red flag for non-accidental injury (NAI). According to RCPCH and NICE guidelines, any suspicion of NAI mandates an immediate safeguarding referral to social services and a senior paediatric review. The primary duty of the clinician in this scenario is to ensure the child's immediate and future safety, which takes precedence over all other considerations.

Further investigations, including a full skeletal survey and ophthalmology review, are required as part of the child protection assessment.

WRONG ANSWER ANALYSIS:

Option A (The injury is consistent with the history provided) is incorrect as a simple roll from a sofa cannot generate the torsional force required to cause a spiral femoral fracture.

Option B (The child likely has osteogenesis imperfecta) is incorrect because while a differential diagnosis, NAI is significantly more prevalent and the injury pattern is more typical of inflicted trauma than a primary bone disorder.

Option D (The fracture requires immediate surgical fixation) is incorrect because although orthopaedic management is essential, the immediate priority is the child's safety and initiating safeguarding procedures.

Option E (The child should be discharged with analgesia) is incorrect as discharging a child with a femoral fracture and high suspicion of NAI would be negligent and place them at risk of further harm.

CORRECT ANSWER:

The description of a bone failing on the tension side while only bending on the compression side is the definition of a greenstick fracture. This incomplete fracture pattern is characteristic in children due to the higher collagen content and porosity of their bones, which allows for greater plastic deformation before complete failure.

When a bending or angulation force is applied, the convex side (tension side) breaks, while the concave side (compression side) bends. This is analogous to attempting to break a young, green branch from a tree, hence the name.

WRONG ANSWER ANALYSIS:

Option A (Torus (Buckle) fracture) is incorrect because it is an impaction fracture resulting from a compression force, causing the cortex to buckle outwards, not break on one side.

Option B (Plastic deformation) is incorrect as it describes a bowing of the bone without a visible cortical fracture line, whereas this X-ray shows a clear break.

Option C (Complete oblique fracture) is incorrect because the fracture described is incomplete, not a complete fracture that extends through both cortices at an oblique angle.

Option E (Salter-Harris Type II) is incorrect as this classification specifically relates to fractures that involve the physis or growth plate, which is not mentioned in this scenario.

CORRECT ANSWER:

The clinical scenario describes a Torus, or Buckle, fracture. This is a stable, incomplete fracture pattern frequently seen in children following a fall onto an outstretched hand.

The mechanism involves a longitudinal compression force applied to the metaphysis of a long bone, most commonly the distal radius. Due to the unique biomechanical properties of paediatric bones, which are more porous and less brittle than adult bones, the cortex fails in compression and buckles outwards.

The key radiological feature is a 'bulge' or wrinkle in the cortex on one side, while the cortex on the opposite side remains intact, distinguishing it from other fracture types.

WRONG ANSWER ANALYSIS:

Option A (Greenstick fracture) is incorrect as it is a tension-related injury where one cortex breaks while the other cortex bends but does not break.

Option C (Salter-Harris Type I) is incorrect because this fracture involves a slip directly through the physis (growth plate) and does not typically present as a cortical bulge.

Option D (Spiral fracture) is incorrect as it is caused by a twisting or rotational force, resulting in a spiral-shaped fracture line.

Option E (Complete transverse fracture) is incorrect because the fracture line extends through both cortices, which contradicts the finding of one intact cortex in this case.

CORRECT ANSWER:

The most appropriate initial imaging is an X-ray of the pelvis including anteroposterior (AP) and frog-leg lateral views.

Slipped Upper Femoral Epiphysis (SUFE) presents with knee pain in up to 50% of cases due to referred pain via the obturator nerve. Therefore, imaging must be directed at the hip, which is the source of the pathology.

Crucially, SUFE is a bilateral condition in 20-40% of patients at presentation, so both hips must be imaged to avoid missing a contralateral slip. An AP pelvis view allows for a direct comparison of both hips, including an assessment of Klein's line.

The frog-leg lateral view is the most sensitive plain radiograph for demonstrating posterior displacement of the femoral epiphysis, which can be subtle on the AP view. This two-view pelvic X-ray is the established first-line investigation for suspected SUFE.

WRONG ANSWER ANALYSIS:

Option A (X-ray of the right knee) is incorrect because the knee pain is referred from the hip pathology, and a knee X-ray will not demonstrate the SUFE.

Option B (X-ray of the right hip - AP and frog-lateral) is incorrect as it fails to image the contralateral hip, creating a significant risk of missing bilateral disease.

Option D (MRI scan of the pelvis) is incorrect as a first-line test; while highly sensitive for pre-slip changes, it is less accessible and not the standard initial diagnostic modality.

Option E (CT scan of the right hip) is incorrect because it is not used for initial diagnosis and exposes the patient to a significantly higher radiation dose than plain radiography.

CORRECT ANSWER:

For an infant diagnosed with Developmental Dysplasia of the Hip (DDH) at 6 months, the window for effective treatment with a dynamic abduction orthosis like a Pavlik harness is closing or has passed.

At this age, established soft tissue contractures and secondary changes in the acetabulum often prevent successful hip reduction with a harness alone. Therefore, the standard and most appropriate management is to proceed with an examination under anaesthesia and an attempt at closed reduction. If the hip is successfully reduced, its position is maintained by applying a hip spica cast for a period of several months to allow the joint to stabilise. This approach is consistent with national guidelines for late-presentation DDH.

WRONG ANSWER ANALYSIS:

Option A (Reassurance) is incorrect as DDH will not resolve spontaneously at this age and requires active intervention to prevent long-term complications like osteoarthritis and gait abnormalities.

Option B (Pavlik harness) is less appropriate because its success rate significantly decreases after approximately 4-6 months of age due to increased hip stiffness.

Option D (Open reduction and femoral osteotomy) is incorrect as it is a more invasive surgical procedure reserved for cases where closed reduction fails or for children diagnosed at an older age (typically over 18 months).

Option E (Physiotherapy and serial X-rays) is incorrect because physiotherapy alone cannot achieve or maintain reduction of a dislocated hip, which is the primary goal of treatment.

CORRECT ANSWER:

The clinical presentation of an obese adolescent male with a limp and referred knee pain, coupled with reduced internal hip rotation, is pathognomonic for a Slipped Upper Femoral Epiphysis (SUFE).

In SUFE, the femoral epiphysis displaces posteriorly and medially. This posterior slip can be subtle or entirely missed on a standard Antero-Posterior (AP) radiograph. Therefore, a 'frog-leg' lateral view is the essential next investigation. This specific projection positions the hip in flexion, abduction, and external rotation, providing a tangential view of the femoral head-neck junction that clearly demonstrates the posterior displacement of the epiphysis. It is the most direct, cost-effective, and appropriate radiological step to confirm the diagnosis as per established guidelines.

WRONG ANSWER ANALYSIS:

Option A (MRI scan of the left knee) is incorrect because the clinical findings point unequivocally to hip pathology, with the knee pain being a classic example of referred pain.

Option B (CT scan of the pelvis) is incorrect as it is not a first-line investigation for SUFE and exposes the patient to a significantly higher radiation dose than plain radiography.

Option D (Ultrasound of the left hip) is incorrect because it is primarily used to detect joint effusions, as seen in transient synovitis, and cannot adequately visualise the bony anatomy to diagnose an epiphyseal slip.

Option E (Bone scan) is incorrect as it is a functional study for conditions with high bone turnover like osteomyelitis or stress fractures, which are not suggested by this classic SUFE presentation.

CORRECT ANSWER:

According to UK national screening guidelines, breech presentation at or after 36 weeks gestation is a major risk factor for Developmental Dysplasia of the Hip (DDH). Selective screening with a hip ultrasound is therefore mandatory for this infant, irrespective of the reassuring findings on the neonatal examination.

A normal clinical examination does not exclude underlying acetabular dysplasia. The ultrasound is scheduled at 4-6 weeks of age. This timing is critical as it allows for the natural resolution of physiological ligamentous laxity common in newborns, thereby reducing the incidence of false-positive scans and preventing unnecessary treatment.

WRONG ANSWER ANALYSIS:

Option A (Reassure parents and discharge) is incorrect because the significant risk factor of breech presentation mandates further imaging regardless of a normal initial examination.

Option C (Arrange hip ultrasound before discharge) is inappropriate because performing an ultrasound in the immediate neonatal period has a high false-positive rate due to physiological laxity.

Option D (Arrange pelvic X-ray at 6 months) is incorrect as ultrasound is the investigation of choice in infants under 4-6 months, because the femoral head is largely cartilaginous and not yet ossified.

Option E (Refer to orthopaedic clinic at 6 weeks) is incorrect as referral is only indicated after an abnormal clinical examination or abnormal ultrasound result; the ultrasound is the appropriate next step.

CORRECT ANSWER:

C because the patient's age and the severity of the disease indicate a poor prognosis without active intervention.

In children over 8 years old with significant femoral head involvement (Catterall group III or IV), the potential for spontaneous, congruent remodelling is low. The primary management goal is to contain the femoral head within the acetabulum to act as a mould during the re-ossification phase, thereby preventing permanent deformity.

Surgical containment, most commonly through a varus femoral osteotomy, is the most effective method to achieve this in a child of this age with these radiological and clinical findings. This approach aims to improve the long-term outcome by preserving a more spherical femoral head and reducing the risk of premature osteoarthritis.

WRONG ANSWER ANALYSIS:

Option A (Observation and physiotherapy only) is incorrect because this conservative approach is typically reserved for younger children (under 6) with less severe disease who have a much better intrinsic capacity for remodelling.

Option B (Non-weight bearing and bed rest) is incorrect as prolonged immobilisation is no longer standard practice due to complications like muscle atrophy and joint stiffness, with little evidence it alters the natural history of the disease.

Option D (Pavlik harness) is incorrect because it is a treatment for developmental dysplasia of the hip in infants and is not used for managing Perthes disease in an 8-year-old.

Option E (Long-term NSAID therapy only) is incorrect because while non-steroidal anti-inflammatory drugs manage symptoms like pain and inflammation, they do not address the underlying biomechanical problem or prevent femoral head deformity.

CORRECT ANSWER:

The Graf classification is used to interpret neonatal hip ultrasounds. An alpha angle greater than 60 degrees indicates a mature, normal hip. An alpha angle between 50 and 59 degrees in an infant under 3 months is classified as a Type IIa hip, signifying physiological immaturity.

In this case, the right hip (alpha 62°) is normal, while the left hip (alpha 55°) is immature. According to UK practice and national screening guidelines, the appropriate management for a Graf Type IIa hip at this age is a period of observation to allow for spontaneous maturation. Therefore, a follow-up ultrasound scan is correctly scheduled for 6 weeks of age to reassess the hip's development. This active monitoring approach avoids unnecessary treatment while ensuring any failure to mature is detected promptly.

WRONG ANSWER ANALYSIS:

Option A (Normal study; discharge) is incorrect because the left hip's alpha angle of 55° falls into the immature category and mandates follow-up imaging.

Option B (Bilateral severe DDH; refer for Pavlik harness) is incorrect as the right hip is normal and the left hip is only immature, not severely dysplastic, which would not typically require immediate harnessing.

Option D (Left hip normal, Right hip immature; repeat USS at 6 weeks) is incorrect because it reverses the interpretation of the reported alpha angles.

Option E (Bilateral hip effusions; refer to orthopaedics) is incorrect as alpha angles assess acetabular morphology for developmental dysplasia of the hip, not the presence of joint fluid.

CORRECT ANSWER:

C (Avascular necrosis). This case describes an unstable Slipped Upper Femoral Epiphysis (SUFE), defined by the patient's inability to weight-bear.

The pathophysiology of this condition involves the displacement of the femoral head (epiphysis) from the femoral neck (metaphysis) through the physis. In an unstable slip, this displacement is acute and severe, leading to a high risk of disrupting the precarious blood supply to the femoral head, primarily from the medial circumflex femoral artery.

This vascular compromise can lead to ischaemia and subsequent avascular necrosis (AVN) of the femoral head. AVN is the most serious and devastating complication in the medium to long term, often resulting in femoral head collapse and necessitating complex surgical intervention. The risk of AVN in unstable SUFE is reported to be as high as 50%, making it the primary concern.

WRONG ANSWER ANALYSIS:

Option A (Limb length discrepancy) is incorrect as it is a potential but less severe complication, often manageable with conservative measures or less complex surgery.

Option B (Early-onset osteoarthritis) is incorrect because while it is a very common long-term outcome, it is frequently a direct consequence of AVN or the altered joint mechanics, making AVN the more primary serious complication.

Option D (Chronic pain syndrome) is less appropriate as it is a non-specific potential outcome of many orthopaedic conditions, whereas AVN is a distinct and severe pathological complication directly related to the unstable slip.

Option E (Femoroacetabular impingement) is incorrect because although it is a common sequela of a healed SUFE, it is a less severe complication than the catastrophic femoral head collapse associated with AVN.

CORRECT ANSWER:

C because the main blood supply to the femoral head in a child is from the medial circumflex femoral artery. This artery gives rise to the lateral and posterior retinacular arteries, which are the primary conduits for blood flow to the femoral epiphysis.

In Perthes disease, the idiopathic avascular necrosis of the capital femoral epiphysis is caused by the disruption of this crucial blood supply. The exact aetiology of the disruption remains unclear, but the consequence is ischaemia and subsequent necrosis of the bone. Understanding this specific vascular anatomy is fundamental to grasping the pathophysiology of the condition.

WRONG ANSWER ANALYSIS:

Option A (Obturator artery) is incorrect because although it contributes a small amount of blood via the artery of the ligamentum teres, this supply is insufficient to prevent necrosis if the main supply is compromised.

Option B (Profunda femoris artery) is incorrect as it is the main deep artery of the thigh from which the circumflex arteries originate, but it does not directly supply the femoral head itself.

Option D (Lateral circumflex femoral artery) is incorrect because it primarily supplies the muscles of the thigh and makes a much smaller contribution to the femoral head's blood supply compared to the medial circumflex artery.

Option E (Femoral artery) is incorrect as it is the principal artery of the lower limb, and while the medial circumflex femoral artery is a branch of it (often via the profunda femoris), it is not the vessel directly and primarily compromised.

CORRECT ANSWER:

Asymmetrical or limited hip abduction is a significant clinical finding and is considered a late sign of Developmental Dysplasia of the Hip (DDH). The negative Ortolani and Barlow tests in this context do not provide reassurance; instead, they suggest the hip may be dislocated but is no longer reducible, representing an established or "fixed" dislocation.

National guidelines, such as those from NICE, mandate an urgent referral (to be seen within 2 weeks) to a paediatric orthopaedic specialist for any infant with a positive clinical finding suggestive of DDH. The specialist will then coordinate the necessary imaging, which is typically an ultrasound scan for an infant of this age, and subsequent management. The key responsibility of the primary care clinician is the urgent referral to the specialist service, not arranging investigations directly.

WRONG ANSWER ANALYSIS:

Option A (Reassure and review at 4 months) is incorrect as limited hip abduction is a red flag for DDH that requires immediate action, not observation.

Option B (Refer for a plain X-ray of the hips) is incorrect because ultrasound is the investigation of choice in infants under 4-6 months due to the cartilaginous nature of the femoral head.

Option C (Refer for an urgent hip ultrasound) is less appropriate because the standard UK pathway is referral to the orthopaedic specialist who then arranges the definitive imaging.

Option E (Advise physiotherapy referral) is incorrect as physiotherapy is not the primary treatment for a suspected dislocated hip, which requires specialist orthopaedic assessment first.

CORRECT ANSWER:

Slipped Upper Femoral Epiphysis (SUFE) involves the displacement of the capital femoral epiphysis from the femoral neck through the physis (growth plate). The slippage is typically posterior and medial.

Klein's line is a radiological line drawn along the superior border of the femoral neck on an anteroposterior (AP) pelvic radiograph. In a normal hip, this line should intersect the lateral aspect of the superior femoral epiphysis. In SUFE, due to the postero-medial displacement of the epiphysis, Klein's line fails to intersect the epiphysis, or intersects a smaller portion of it. This is considered the earliest and most reliable radiological sign of SUFE on an AP view, often referred to as Trethowan's sign.

WRONG ANSWER ANALYSIS:

Option B (Widening of the medial joint space) is incorrect as this can be a feature of Perthes disease or joint effusion, not SUFE.

Option C (Sclerosis and fragmentation of the femoral head) is incorrect because these are the classical radiological features of avascular necrosis, characteristic of Perthes disease.

Option D (A shallow acetabular index) is incorrect as this is a measurement used to diagnose developmental dysplasia of the hip (DDH).

Option E (Periosteal reaction along the femoral neck) is incorrect as this finding would suggest pathology such as a healing fracture, osteomyelitis, or a bone tumour rather than SUFE.

CORRECT ANSWER:

D, femoral head extrusion. Perthes disease is an idiopathic avascular necrosis of the femoral head. The process involves fragmentation and subsequent re-ossification.

During the fragmentation stage, the femoral head is structurally weak and can deform. Femoral head extrusion, or subluxation, occurs when this weakened head is displaced laterally and is no longer contained within the acetabulum. This is a significant poor prognostic factor.

The sudden increase in pain and, critically, the new loss of abduction are the classic clinical signs of this event. The extruded head creates a mechanical block, preventing the hip from abducting. This finding often necessitates surgical intervention, such as a containment osteotomy, to improve the long-term outcome.

WRONG ANSWER ANALYSIS:

Option A (Slipped upper femoral epiphysis) is incorrect as it typically affects older, adolescent children during their pubertal growth spurt, not a 6-year-old.

Option B (Avascular necrosis) is incorrect because it is the underlying pathological process of Perthes disease itself, not an acute complication explaining the sudden deterioration.

Option C (Pathological fracture) is less likely as the specific sign of new-onset loss of abduction points directly to the mechanical block caused by femoral head extrusion.

Option E (Septic arthritis) is unlikely in the absence of systemic features such as fever or significantly raised inflammatory markers.

CORRECT ANSWER:

Female gender is a significant non-modifiable risk factor for Developmental Dysplasia of the Hip (DDH), with an incidence approximately four to six times higher in females than in males.

This increased prevalence is attributed to the effects of maternal relaxin hormone on ligamentous laxity in the female infant. The Newborn and Infant Physical Examination (NIPE) screening pathway, therefore, considers female gender as a risk factor, not male gender.

The primary aim of the NIPE pathway is to identify infants at higher risk who require selective ultrasound screening of their hips to ensure early detection and management, thereby preventing long-term complications such as osteoarthritis and mobility issues.

WRONG ANSWER ANALYSIS:

Option A (Breech presentation at or after 36 weeks) is incorrect because it is a major risk factor for DDH due to the mechanical forces exerted on the developing hip joints, mandating a screening ultrasound.

Option B (First-degree family history of hip problems) is incorrect as a positive family history significantly increases the incidence of DDH, and it is a key indication for selective ultrasound screening under NIPE guidelines.

Option C (Oligohydramnios) is incorrect because, like other "packaging disorders," it restricts foetal movement in-utero, which is a recognised contributor to the development of hip dysplasia.

Option E (Talipes equinovarus) is incorrect as this fixed foot deformity is associated with an increased risk of DDH, and infants with this condition are also referred for a hip ultrasound.

CORRECT ANSWER:

The definitive treatment for a Slipped Upper Femoral Epiphysis (SUFE) is urgent surgical stabilisation. The underlying pathology is a mechanical failure through the hypertrophic zone of the capital femoral physis, causing displacement of the epiphysis on the femoral neck.

The primary goal of treatment is to prevent further slippage, which would increase the risk of severe complications such as avascular necrosis and chondrolysis. The established gold-standard procedure is in-situ fixation with a single cannulated screw placed through the femoral neck and across the physis into the centre of the femoral head. This provides immediate mechanical stability and encourages premature physeal closure, thus resolving the instability permanently.

WRONG ANSWER ANALYSIS:

Option A (Serial casting) is incorrect as it fails to provide the rigid internal fixation necessary to prevent further displacement of the femoral epiphysis.

Option C (Long-term bed rest and traction) is incorrect because it is not a definitive treatment and does not provide the stable fixation required for physeal fusion and healing.

Option D (A course of high-dose steroids) is incorrect as SUFE is a mechanical condition, not an inflammatory one, and steroids have no therapeutic role.

Option E (Arthroscopic joint washout) is incorrect because this procedure is indicated for conditions like septic arthritis, not for addressing the fundamental instability of a slipped epiphysis.

CORRECT ANSWER:

The most appropriate next step is a plain X-ray of the pelvis. In an infant aged 6 months, the femoral head has begun to ossify, which makes ultrasound imaging less reliable.

Therefore, according to NICE guideline NG78 and established paediatric orthopaedic practice, an anteroposterior pelvis X-ray is the definitive first-line investigation for suspected developmental dysplasia of the hip (DDH) in this age group. The presence of significant clinical findings such as asymmetrical creases and a positive Galeazzi sign (leg length discrepancy) mandates urgent imaging to confirm the diagnosis and facilitate timely referral to paediatric orthopaedics.

WRONG ANSWER ANALYSIS:

Option A (Reassure parents) is incorrect because new, abnormal clinical signs of DDH require investigation, even if the newborn examination was normal.

Option B (Refer for a hip ultrasound scan) is incorrect as this is the preferred investigation for infants under 4.5 months, after which its diagnostic accuracy diminishes due to femoral head ossification.

Option D (Refer directly to paediatric physiotherapy) is inappropriate because a diagnosis must be confirmed with imaging before any management plan, which would be led by an orthopaedic surgeon, is initiated.

Option E (Advise review by GP in 1 month) is incorrect as it would cause an unacceptable delay in diagnosing and managing a condition where early intervention is critical to prevent long-term morbidity.

CORRECT ANSWER:

The patient's age (five years) and radiological findings of a contained femoral head are key prognostic factors that guide management. In children under six with good hip range of motion, the prognosis for femoral head remodelling is excellent.

Therefore, UK clinical practice advocates for a conservative, non-operative approach. The primary goals are symptomatic relief and maintenance of hip function. This involves activity modification, simple analgesia such as NSAIDs for pain from synovitis, and physiotherapy to preserve the range of motion, particularly hip abduction and internal rotation. Regular clinical and radiographic surveillance is essential to monitor disease progression, but invasive interventions are reserved for older children or those with deteriorating signs, such as loss of containment.

WRONG ANSWER ANALYSIS:

Option A (Strict bed rest and non-weight bearing) is incorrect because prolonged immobilisation is associated with joint stiffness and muscle atrophy and is no longer standard practice for mild disease.

Option B (Surgical osteotomy) is incorrect as surgery is typically reserved for older children (over 8 years) or those with severe disease showing femoral head extrusion from the acetabulum.

Option D (Pavlik harness) is incorrect because it is a treatment for developmental dysplasia of the hip in infants, not Perthes disease.

Option E (Above-knee plaster cast) is incorrect as casting is a method to enforce containment or restrict weight-bearing in more severe cases, not for initial management in a child with a well-contained femoral head and good movement.

CORRECT ANSWER:

Slipped Upper Femoral Epiphysis (SUFE) has a significant risk of occurring bilaterally. The incidence of a contralateral slip can be as high as 20-40%, particularly in patients with open physes and risk factors such as obesity or underlying endocrinopathies.

Given this high risk, the priority is to prevent a future slip on the asymptomatic side, which can lead to significant morbidity, including avascular necrosis and chondrolysis. NICE guidance acknowledges that treatment for mild-to-moderate slips often involves percutaneous in-situ fixation with or without prophylactic pinning of the contralateral hip. Therefore, prophylactic surgical fixation is the most crucial preventative measure to avoid the long-term complications of a second, potentially more severe, slip.

WRONG ANSWER ANALYSIS:

Option A (Bilateral hip spica casting) is incorrect as it is not a recognised treatment for SUFE and would cause muscle wasting and joint stiffness without preventing a slip.

Option B (Weight loss and physiotherapy) is incorrect because while it is an important long-term goal for managing obesity, it does not provide the immediate physeal stability required to prevent an imminent contralateral slip.

Option D (Long-term NSAID therapy) is incorrect as non-steroidal anti-inflammatory drugs only provide symptomatic pain relief and do not address the underlying mechanical instability of the physis.

Option E (Regular X-ray surveillance every 3 months) is incorrect because a slip can occur acutely between surveillance intervals; this strategy is reactive, not prophylactic, and fails to prevent the initial morbidity of a contralateral event.

CORRECT ANSWER:

An isolated high-pitched 'click' during a hip examination is a common finding. While often benign and originating from soft tissues like ligaments or tendons, it is considered a risk factor for Developmental Dysplasia of the Hip (DDH).

According to UK Newborn and Infant Physical Examination (NIPE) programme guidelines, the presence of a click, even with negative Ortolani and Barlow tests, warrants further investigation. The most appropriate next step is a referral for a hip ultrasound. This is optimally performed at 4-6 weeks of age to allow for the resolution of normal physiological laxity, thereby reducing the rate of false positives, while still allowing for early detection and management of any underlying acetabular dysplasia or instability.

WRONG ANSWER ANALYSIS:

Option A (Refer urgently to orthopaedics) is incorrect because urgent referral is reserved for a confirmed dislocated or dislocatable hip, indicated by a positive Ortolani or Barlow test ('clunk').

Option C (Reassure parents and discharge from NIPE pathway) is inappropriate as an isolated click is a specific indication for further screening, and discharge would risk missing a diagnosis of DDH.

Option D (Advise parents to use double nappies) is incorrect as this is an outdated practice with no evidence to support its effectiveness in preventing or treating DDH.

Option E (Repeat the hip examination in 24 hours) is less appropriate because a definitive finding of a click has already been made, which mandates a referral for imaging rather than just clinical reassessment.

CORRECT ANSWER:

Slipped upper femoral epiphysis (SUFE) is the most probable diagnosis. The patient presents with several key risk factors for atypical SUFE, which occurs in children outside the typical demographic of obese adolescent males.

Both Down syndrome and hypothyroidism are strongly associated with an increased risk of SUFE due to their effects on the physis. The clinical presentation of a new limp and hip pain on passive movement, particularly internal rotation, is characteristic of SUFE. Although she is non-ambulant, a limp can manifest as a reluctance to bear weight or altered positioning.

The absence of fever points away from an infectious aetiology. SUFE is an orthopaedic emergency, and prompt diagnosis with radiographic imaging (AP and frog-leg lateral views of both hips) is crucial to prevent complications such as avascular necrosis and chondrolysis.

WRONG ANSWER ANALYSIS:

Option A (Septic arthritis) is less likely as the patient is afebrile and lacks systemic signs of infection.

Option B (Perthes disease) typically affects a younger age group, most commonly boys between 4 and 8 years old.

Option D (Transient synovitis) is a diagnosis of exclusion, usually seen in younger children, and is less probable given the significant underlying risk factors for SUFE.

Option E (Fracture) is improbable in the absence of any reported history of trauma.

CORRECT ANSWER:

Perthes disease is an idiopathic avascular necrosis of the capital femoral epiphysis. The disruption of the blood supply to the femoral head leads to a predictable sequence of radiological changes.

Initially, the bone dies, which can manifest as increased density (sclerosis) on an X-ray. As the bone is reabsorbed and new bone is laid down, the weakened structure collapses under pressure, leading to the characteristic fragmentation and flattening of the femoral head. This process, known as osteonecrosis, is the pathophysiological hallmark of the condition and the most consistent radiological finding in an established case.

WRONG ANSWER ANALYSIS:

Option A (Posterior and inferior slippage of the femoral epiphysis) is incorrect as this describes Slipped Upper Femoral Epiphysis (SUFE), a condition typically seen in adolescents.

Option B (Lytic lesion in the femoral neck) is incorrect because it suggests a differential diagnosis of a bone cyst, infection such as osteomyelitis, or a tumour, rather than avascular necrosis.

Option D (Acetabular dysplasia with a shallow socket) is incorrect as this is the defining feature of Developmental Dysplasia of the Hip (DDH), usually identified in infancy.

Option E (Coxa vara with a decreased femoral neck-shaft angle) is incorrect because while it can be a secondary deformity, it is not the primary pathological finding which is centred on the femoral head.

CORRECT ANSWER:

Breech presentation at or after 36 weeks gestation is a primary risk factor for Developmental Dysplasia of the Hip (DDH). UK national screening guidelines, specifically the Newborn and Infant Physical Examination (NIPE) programme, mandate a screening hip ultrasound for all babies with this risk factor.

This is required irrespective of the findings on clinical examination, as the NIPE check can be falsely reassuring and may not detect underlying acetabular dysplasia or subtle instability. Although the ideal timing for the scan is between 4 to 6 weeks of age to avoid ambiguity from physiological laxity, it remains the essential and most appropriate investigation for this 10-week-old baby who has missed the initial window. Early detection via ultrasound is crucial for effective management and optimal long-term outcomes.

WRONG ANSWER ANALYSIS:

Option A (Reassure parents) is incorrect because a normal clinical examination does not negate the significant risk of DDH associated with breech presentation, necessitating further imaging.

Option B (Refer for an orthopaedic review at 6 months) is incorrect as it would unacceptably delay the diagnosis and potential treatment of DDH, which is most effective when initiated early.

Option D (Refer for a plain X-ray) is incorrect because the infant hip is predominantly cartilaginous before 4-6 months of age, making ultrasound the superior and appropriate imaging modality.

Option E (Advise double nappies) is incorrect as this practice has no proven therapeutic benefit in the prevention or management of DDH and must not replace definitive screening.

CORRECT ANSWER:

The clinical presentation is classic for an unstable Slipped Upper Femoral Epiphysis (SUFE), likely an acute-on-chronic event given the preceding trauma. The patient's age and high BMI are significant risk factors.

In an unstable SUFE, the femoral epiphysis has displaced from the metaphysis, and there is a high risk of further slippage with any movement. The most critical immediate step is to prevent this, as further displacement can compromise the tenuous blood supply to the femoral head, leading to avascular necrosis (AVN), a devastating complication.

Therefore, enforcing strict non-weight bearing is the absolute priority. Making the patient nil by mouth (NBM) is concurrently essential to prepare for urgent surgical stabilisation, which is the definitive treatment. This dual approach minimises the risk of AVN and prepares for timely surgical intervention.

WRONG ANSWER ANALYSIS:

Option A (Administer IV antibiotics) is incorrect as there are no features to suggest septic arthritis, such as fever or systemic upset.

Option C (Administer a stat dose of IV morphine) is incorrect because while analgesia is important, preventing further slippage and subsequent avascular necrosis is the immediate, limb-saving priority.

Option D (Request an urgent CT scan) is incorrect as anteroposterior (AP) and frog-leg lateral plain radiographs are the gold-standard first-line investigations for diagnosing SUFE.

Option E (Apply skin traction to the affected leg) is incorrect as traction is not routinely recommended and may increase intracapsular pressure, potentially worsening ischaemic risk to the femoral head.

CORRECT ANSWER:

The Barlow manoeuvre is a provocative test used to screen for developmental dysplasia of the hip (DDH) during the Newborn and Infant Physical Examination (NIPE).

The procedure described involves adducting the hip while applying gentle posterior pressure. A positive test is the sensation of the femoral head slipping or 'clunking' out of the acetabulum, which indicates that the hip is unstable and dislocatable.

This manoeuvre, along with the Ortolani test, forms the cornerstone of clinical screening for DDH in neonates as recommended by UK national screening guidelines. Its purpose is to identify instability, prompting further investigation, typically with an ultrasound scan, to prevent long-term complications such as gait abnormalities and osteoarthritis.

WRONG ANSWER ANALYSIS:

Option A (Ortolani test) is incorrect because it is a reduction manoeuvre used to relocate an already dislocated femoral head by abducting the hip, not a test to provoke dislocation.

Option C (Galeazzi sign) is incorrect as it is an observational sign of femoral shortening, identified by unequal knee heights when the hips and knees are flexed, not a dynamic hip stability test.

Option D (Trendelenburg test) is incorrect because it assesses hip abductor muscle weakness in an ambulatory child and is not performed on a neonate.

Option E (Thomas test) is incorrect as it is used to detect a fixed flexion deformity of the hip and is not relevant to assessing neonatal hip instability.

CORRECT ANSWER:

Perthes disease. This condition represents idiopathic avascular necrosis of the femoral head. The peak age of incidence is 4 to 8 years, fitting this 6-year-old boy.

The presentation is typically insidious over several weeks with a progressive, often painless, limp that worsens with activity towards the end of the day. Examination findings of restricted abduction and internal rotation are classical signs resulting from the altered shape of the femoral head and associated joint irritability. A positive Trendelenburg sign indicates weakness of the hip abductor muscles, which is a common functional consequence of the underlying hip pathology. The afebrile and systemically well state is also characteristic of this non-infectious, vascular condition.

WRONG ANSWER ANALYSIS:

Option A (Transient synovitis) is incorrect because it presents as an acute, painful limp that typically resolves within one to two weeks, not over a four-week period.

Option C (Slipped upper femoral epiphysis) is less likely as it characteristically affects obese adolescents during their pubertal growth spurt, not a 6-year-old child.

Option D (Developmental dysplasia of the hip) is incorrect as it is usually detected in infancy through neonatal screening programmes and would not typically present for the first time at this age.

Option E (Septic arthritis) is incorrect because the child would be systemically unwell, febrile, and present with an acute, non-weight-bearing, and severely painful joint.

CORRECT ANSWER:

Slipped upper femoral epiphysis (SUFE) is the most probable diagnosis. This condition involves the displacement of the femoral head from the femoral neck through the growth plate.

The typical patient is an obese adolescent boy, matching the boy's description. The presentation of knee pain is a classic feature of hip pathology due to referred pain via the obturator nerve. Examination findings are crucial: an unremarkable knee with a painful hip, particularly with restricted internal rotation, is the cardinal sign of SUFE. The antalgic limp and a sub-acute history of three weeks are also highly characteristic. Early diagnosis and surgical stabilisation are vital to prevent complications like avascular necrosis and chondrolysis.

WRONG ANSWER ANALYSIS:

Option A (Osgood-Schlatter disease) is incorrect as it would present with pain and tenderness localised to the tibial tuberosity, not the hip.

Option B (Perthes disease) is less likely because it typically affects younger children, usually between the ages of 4 and 8.

Option C (Septic arthritis) is incorrect due to the sub-acute presentation; septic arthritis is an acute condition accompanied by systemic signs such as fever.

Option E (Juvenile idiopathic arthritis) is less likely as it typically presents with signs of inflammation, such as joint swelling and morning stiffness, which are absent here.

CORRECT ANSWER:

The clinical scenario describes the Ortolani test, which is used to detect a dislocated hip in a neonate. The test involves gentle abduction of the flexed hip, during which the examiner's fingers lift the greater trochanter.

A positive test is indicated by a palpable and often audible 'clunk' as the dislocated femoral head relocates into the acetabulum. This is a key finding in Developmental Dysplasia of the Hip (DDH). According to the national NIPE (Newborn and Infant Physical Examination) pathway and NICE guidelines, a confirmed positive Ortolani test signifies an unstable or dislocated hip, which is a high-risk finding.

Therefore, the most appropriate and critical next step is an urgent referral to a paediatric orthopaedic service, typically for assessment within two weeks. Early specialist assessment and management, often with a Pavlik harness, are crucial to ensure normal hip joint development and prevent long-term complications such as osteoarthritis.

WRONG ANSWER ANALYSIS:

Option A (Barlow test; refer urgently to orthopaedics) is incorrect because the Barlow test aims to dislocate an unstable hip by adducting it with posterior pressure, which is the opposite of the manoeuvre described.

Option C (Barlow test; review in 6-8 weeks) is incorrect as it misidentifies the test and suggests an inappropriate delay in management for a significant clinical finding.

Option D (Ortolani test; reassure and discharge) is incorrect because while it correctly identifies the test, reassurance and discharge are inappropriate and potentially negligent for a positive Ortolani sign.

Option E (Galeazzi sign; perform hip ultrasound) is incorrect because the Galeazzi sign involves observing for knee height asymmetry, a different clinical test, and the primary next step is urgent referral, not just ordering an ultrasound.

CORRECT ANSWER:

Option A is the correct answer. Night pain severe enough to wake a child is a significant red flag for malignancy, particularly leukaemia or bone tumours such as osteosarcoma.

The pathophysiology relates to the infiltration of the bone marrow by malignant cells, which increases intramedullary pressure. This pressure change is often more pronounced at night, leading to a deep, boring pain that is distinct from the discomfort of inflammatory or mechanical conditions.

This symptom, especially when accompanied by other systemic features like lethargy, weight loss, or bruising, warrants urgent investigation to exclude a neoplastic process. While infection remains a common cause of limp, this specific pain characteristic is highly suspicious for malignancy.

WRONG ANSWER ANALYSIS:

Option B (Reluctance to walk in the morning) is incorrect as prominent morning stiffness and gelling are classic features of inflammatory conditions like Juvenile Idiopathic Arthritis.

Option C (A preceding viral illness) is incorrect because this history typically points towards benign, self-limiting causes such as transient synovitis or viral myositis.

Option D (A sibling with juvenile idiopathic arthritis) is incorrect as, while it may slightly increase the suspicion for JIA due to genetic predisposition, it does not suggest a malignant cause.

Option E (Pain that is worse after exercise) is incorrect as this pattern is characteristic of mechanical pain or overuse injuries, not malignancy.

CORRECT ANSWER:

C-reactive protein (CRP) is the most sensitive and specific inflammatory marker for monitoring the response to treatment in septic arthritis.

Produced by the liver in response to inflammation, CRP has a short half-life of approximately 19 hours. This means its levels rise rapidly during acute infection and, crucially, fall swiftly with effective antimicrobial therapy, providing a near real-time indication of treatment success. National guidelines recommend monitoring CRP to guide the duration of antibiotic therapy and the switch from intravenous to oral administration. A significant and sustained fall in CRP is a key indicator that the infection is resolving.

WRONG ANSWER ANALYSIS:

Option A (White cell count) is less reliable as it can normalise quickly, even while the infection is still active, and is non-specific.

Option C (Erythrocyte sedimentation rate) is incorrect because the ESR has a long half-life and lags significantly behind the clinical picture, remaining elevated for weeks after the infection has resolved.

Option D (Serial X-rays) are not useful for monitoring acute treatment response but are indicated for assessing long-term complications like bony destruction or growth plate damage.

Option E (Clinical examination of joint range) is a vital part of the overall assessment but is not the most important single marker for tracking the resolution of the underlying infection itself.

CORRECT ANSWER:

While a spiral fracture of the tibia in a child of this age is often an accidental injury, commonly known as a "Toddler's Fracture," safeguarding principles are paramount. National guidelines from NICE and the RCPCH mandate that non-accidental injury (NAI) must be actively considered and excluded in any young or pre-mobile child presenting with a fracture.

The most critical step is to take a thorough history to ensure the explanation for the injury is developmentally appropriate and consistent with the clinical findings. The priority is the child's safety, and therefore a comprehensive NAI assessment must be the first consideration before attributing the injury to an accident. This initial assessment determines the need for further investigations, such as a full skeletal survey, or referral to social care.

WRONG ANSWER ANALYSIS:

Option A (Referral to rheumatology) is incorrect as there are no features in the presentation, such as joint swelling or systemic upset, to suggest an underlying inflammatory or rheumatological condition.

Option C (Vitamin D and calcium levels) is incorrect because investigating for metabolic bone disease is a secondary consideration and not the immediate priority in an otherwise well child with an acute fracture.

Option D (A skeletal survey for bone dysplasia) is incorrect as this is a specific investigation for a suspected underlying bone fragility disorder, which is not the primary concern without other clinical indicators.

Option E (Admission for IV antibiotics) is incorrect because this is a closed fracture with no evidence of being open or infected, thus antibiotic therapy is not indicated.

CORRECT ANSWER:

Septic arthritis of the hip is a paediatric emergency. The hip joint is an end-arterial circulation, making the femoral head epiphysis particularly vulnerable to ischaemia.

In septic arthritis, the accumulation of inflammatory exudate and pus within the joint capsule significantly increases intra-articular pressure. This pressure can tamponade the retinacular vessels that supply the femoral head, leading to a compromise in blood flow.

If surgical drainage and antibiotic therapy are delayed, this interruption to the blood supply results in avascular necrosis (AVN) of the femoral head. The necrotic bone eventually collapses, leading to severe joint destruction, pain, and long-term disability. This is the most devastating long-term complication directly resulting from delayed treatment.

WRONG ANSWER ANALYSIS:

Option A (Chronic pain syndrome) is less specific, as chronic pain is a potential outcome of several complications, including AVN and osteoarthritis, rather than the primary pathological process.

Option B (Recurrent dislocations) is incorrect because septic arthritis causes inflammation and scarring which typically stiffens the joint, making dislocation less likely.

Option D (Limb length discrepancy) can occur, but it is usually a secondary consequence of femoral head collapse from avascular necrosis or physeal damage, not the most common primary complication.

Option E (Early-onset osteoarthritis) is a very likely long-term sequela, but it develops as a result of the joint surface damage caused by the initial infection and, more significantly, by the preceding avascular necrosis.

CORRECT ANSWER:

Ultrasound is the first-line and most appropriate initial imaging investigation for suspected septic arthritis. It is a rapid, non-invasive, and radiation-free modality that is highly sensitive for detecting joint effusions.

In a young, distressed child, its bedside availability is a significant advantage. Crucially, ultrasound can also guide the subsequent diagnostic and therapeutic joint aspiration, which is essential for obtaining synovial fluid for microscopy and culture to confirm the diagnosis and direct antibiotic therapy. National guidelines recommend ultrasound as the primary investigation to confirm an effusion before more complex imaging is considered.

Prompt identification and drainage of a septic joint is critical to prevent long-term complications such as cartilage damage and growth disturbance.

WRONG ANSWER ANALYSIS:

Option A (Plain X-ray) is less appropriate because radiographs are often normal in the early stages of septic arthritis and are insensitive for visualising a joint effusion, although they can help exclude other diagnoses like fractures or tumours.

Option B (CT scan) is incorrect as it exposes the child to significant ionising radiation and is less sensitive than ultrasound for detecting soft tissue swelling and fluid collections.

Option C (MRI scan) is not the most useful initial step as it is resource-intensive, time-consuming, and often requires sedation or general anaesthesia in a 5-year-old, making it impractical for rapid diagnosis.

Option E (Bone scan) is incorrect because scintigraphy is non-specific; while it can show inflammation, it cannot reliably differentiate between septic arthritis, osteomyelitis, or overlying cellulitis.

CORRECT ANSWER:

Transient synovitis, or irritable hip, is a self-limiting inflammatory condition of the synovial membrane of the hip joint. The pathophysiology involves an acute, sterile inflammation, leading to a joint effusion and pain.

The primary goal of management is to reduce this inflammation and provide effective analgesia. Non-steroidal anti-inflammatory drugs (NSAIDs) are the most appropriate first-line treatment as they directly target the underlying inflammatory cascade by inhibiting prostaglandin synthesis. Ibuprofen is a safe and effective NSAID commonly used in paediatrics for mild to moderate inflammatory pain. Its dual action of providing analgesia and reducing inflammation makes it superior to simple analgesics in this clinical context. Current UK practice guidelines advocate for the use of NSAIDs as the mainstay of symptomatic relief in transient synovitis, alongside a period of rest.

WRONG ANSWER ANALYSIS:

Option A (Paracetamol only) is less appropriate because, while it provides analgesia, it has minimal anti-inflammatory effects and would not address the underlying cause of the pain as effectively as an NSAID.

Option C (Oral codeine) is incorrect as it is an opiate with a significant side-effect profile and is not recommended for children due to unpredictable metabolism and the risk of respiratory depression.

Option D (Oral naproxen) is also an NSAID, but ibuprofen is generally preferred as the first-line choice in children for acute conditions due to its well-established safety profile and shorter duration of action.

Option E (Oral morphine) is inappropriate as it is a potent opioid analgesic reserved for severe pain, which is not characteristic of transient synovitis.

CORRECT ANSWER:

Current UK practice for uncomplicated acute haematogenous osteomyelitis is a sequential intravenous to oral antibiotic "step-down" or "switch" therapy. The key principle is to continue intravenous therapy until the patient shows clear signs of clinical improvement. This includes being systemically well, afebrile for at least 24-48 hours, and having a significant downward trend in inflammatory markers, particularly the C-reactive protein (CRP).

This clinical milestone is typically reached within 3 to 7 days. Evidence suggests that children who meet oral switch criteria within the first week have better outcomes than those requiring longer intravenous courses. This approach minimises the risks of prolonged intravenous access, such as line infections and thrombosis, and reduces the length of hospital stay without compromising treatment efficacy. The total duration of antibiotic treatment (IV and oral combined) is usually 4-6 weeks.

WRONG ANSWER ANALYSIS:

Option A (48-72 hours) is incorrect as this is often the minimum period to assess initial response, and switching this early may be premature if clinical and biochemical improvement is not yet established.

Option C (10-14 days) is incorrect because it reflects an older, more conservative management approach and is generally unnecessary for uncomplicated cases where a timely switch to oral antibiotics is possible.

Option D (4-6 weeks) is incorrect as this represents the typical total duration of combined intravenous and oral antibiotic therapy, not the intravenous portion alone.

Option E (3 months) is incorrect because such a prolonged course of treatment would be reserved for chronic, complex, or refractory osteomyelitis, not an uncomplicated acute presentation.

CORRECT ANSWER:

The most crucial finding that makes septic arthritis less likely is a playful child who is hopping. Septic arthritis is a bacterial infection of the joint space, resulting in severe pain.

A child with septic arthritis is typically systemically unwell, irritable, and holds the affected limb in a fixed position (pseudo-paralysis). They will almost invariably refuse to bear any weight. In contrast, a child who is well, playful, and able to hop, despite a limp, presents a clinical picture highly suggestive of transient synovitis (irritable hip), a self-limiting inflammatory condition.

This overall clinical assessment often provides more diagnostic clarity than initial laboratory findings, which can overlap between the two conditions.

WRONG ANSWER ANALYSIS:

Option A (A small effusion seen on hip ultrasound) is incorrect as a joint effusion is a non-specific finding, present in both transient synovitis and early septic arthritis.

Option B (Pain at the extreme of internal rotation) is incorrect because this sign indicates hip joint inflammation and is characteristic of both septic arthritis and transient synovitis.

Option C (History of a cold one week ago) is incorrect as a preceding viral illness is a classic feature of transient synovitis but does not exclude a subsequent bacterial infection.

Option E (Refusal to bear any weight) is incorrect as this is a significant red flag that dramatically increases the likelihood of septic arthritis.

CORRECT ANSWER:

Septic arthritis of the hip is a surgical emergency. The pathophysiology involves a rapid accumulation of purulent fluid within the fixed space of the joint capsule. This increases intra-articular pressure, which can compromise the precarious blood supply to the femoral head, leading to avascular necrosis and irreversible cartilage damage within hours.

The pus also contains destructive enzymes that degrade the articular cartilage. National guidelines, including those from the British Orthopaedic Association, state that septic arthritis requires surgical drainage as soon as possible, ideally within 24 hours of diagnosis. While intravenous antibiotics are crucial for treating the systemic infection, they cannot effectively penetrate the abscess or remove the destructive inflammatory mediators. Therefore, urgent surgical decompression, irrigation, and drainage is the most critical intervention to preserve joint function and prevent long-term disability.

WRONG ANSWER ANALYSIS:

Option A (High-dose IV antibiotics) is incorrect because although essential, antibiotics alone do not resolve the dangerously high intra-articular pressure or remove the destructive purulent material.

Option C (Application of hip traction) is incorrect as it has no role in treating the acute infection and would inappropriately delay the definitive surgical management required.

Option D (Immobilisation in a plaster cast) is incorrect because it is not a primary treatment, would prevent necessary surgical access, and hinder clinical monitoring of the joint.

Option E (Prolonged course of oral NSAIDs) is incorrect as non-steroidal anti-inflammatory drugs only provide symptomatic relief for pain and inflammation and do not address the underlying infection or prevent joint destruction.

CORRECT ANSWER:

A Toddler's Fracture is a stable, undisplaced or minimally displaced spiral or oblique fracture of the distal tibial diaphysis. The pathophysiology relates to the unique biomechanics of a young child's bone.

It is typically caused by a low-energy torsional force, such as when a toddler's foot is planted and their body rotates. This twisting mechanism creates the characteristic spiral fracture pattern. The thick and strong periosteum in this age group prevents significant displacement, which is why the clinical signs can be subtle, often presenting only as an acute refusal to bear weight with minimal swelling.

The history of a specific injury is frequently absent. This specific fracture pattern is the hallmark radiographic finding consistent with the classic clinical presentation.

WRONG ANSWER ANALYSIS:

Option A (A transverse fracture of the tibial diaphysis) is incorrect as this pattern typically results from a direct, high-energy impact rather than the low-energy rotational force seen in a Toddler's Fracture.

Option B (A buckle fracture of the distal tibia) is incorrect because buckle fractures are compression injuries that occur at the metaphysis, not the diaphysis where a Toddler's Fracture is located.

Option D (Periosteal reaction along the femoral shaft) is incorrect as this finding would indicate a femoral pathology or a healing fracture, and does not match the clinical localisation to the shin.

Option E (Soft tissue swelling only) is incorrect because while swelling may be present, a Toddler's Fracture is a definitive bony injury that, although sometimes subtle, should be visible on radiographs.

CORRECT ANSWER:

This presentation is highly suspicious for septic arthritis, a paediatric emergency requiring prompt inpatient management.

Although the inflammatory markers are only moderately raised, the combination of fever, a warm, swollen, and guarded knee joint necessitates urgent action to prevent irreversible joint damage. National guidance supports admitting children with suspected septic arthritis for intravenous antibiotics. This allows for close monitoring of the clinical response and escalation to surgical intervention if there is no improvement. The initial intravenous therapy covers the most likely causative organisms, primarily Staphylococcus aureus, while awaiting definitive culture results if a joint aspiration is performed.

WRONG ANSWER ANALYSIS:

Option A (Discharge with oral antibiotics) is incorrect because oral administration may not achieve adequate antibiotic concentration within the joint, and the child requires close inpatient monitoring.

Option B (Discharge with NSAIDs and safety netting) is unsafe as it fails to treat the potential bacterial infection, risking significant morbidity.

Option D (Urgent orthopaedic referral for joint washout) is less appropriate as the first step; a trial of intravenous antibiotics is reasonable given the intermediate clinical picture, with surgery reserved for those who do not respond.

Option E (Request an urgent MRI scan) is incorrect because MRI is not the first-line investigation and would delay the crucial initiation of antibiotic therapy.

CORRECT ANSWER:

Transient synovitis is a diagnosis of exclusion. While it is a benign, self-limiting condition, its initial presentation can mimic septic arthritis, a paediatric emergency.

The management priority is therefore effective safety netting. Parents must be given clear, unambiguous advice on when to return for urgent reassessment. The development of a fever or an inability to weight-bear are red flag signs suggestive of a more serious underlying pathology such as septic arthritis, which requires immediate surgical intervention to prevent permanent joint damage.

Symptomatic management with simple analgesia and relative rest is appropriate, but the advice to return if specific symptoms develop is the most critical aspect of the discharge plan to ensure patient safety.

WRONG ANSWER ANALYSIS:

Option A (Strict bed rest for one week) is incorrect as relative rest is sufficient and strict bed rest is unnecessary and often impractical for a young child.

Option C (Follow up with paediatric rheumatology) is incorrect because a referral is not indicated for a first, uncomplicated presentation of transient synovitis.

Option D (An X-ray is required in 2 weeks to rule out Perthes) is incorrect as imaging is only considered if symptoms fail to resolve after several weeks, not as routine follow-up.

Option E (He should be referred for physiotherapy) is incorrect because physiotherapy has no role in the management of this acute, self-resolving inflammatory condition.

CORRECT ANSWER:

Children with sickle cell disease have a significantly increased risk of Salmonella osteomyelitis. The underlying pathophysiology is multifactorial. Functional asplenia, a hallmark of the disease, impairs the clearance of encapsulated bacteria, including Salmonella species.

Furthermore, vaso-occlusive crises can cause microinfarcts in the gut wall, allowing for translocation of Salmonella from the gastrointestinal tract into the bloodstream. These circulating bacteria can then seed areas of bone that have also undergone infarction and necrosis, creating a perfect environment for infection to establish.

While Staphylococcus aureus is the most common causative organism for osteomyelitis in the general paediatric population, this specific and high-risk association with Salmonella in sickle cell disease dictates that empirical antibiotic therapy must provide cover for both pathogens. A third-generation cephalosporin, such as ceftriaxone or cefotaxime, is therefore a standard first-line choice.

WRONG ANSWER ANALYSIS:

Option A (Pseudomonas aeruginosa) is incorrect as it is most commonly associated with osteomyelitis following deep puncture wounds, particularly through footwear.

Option B (Candida albicans) is incorrect because fungal osteomyelitis is rare and typically occurs in severely immunocompromised children or those with long-term indwelling central lines.

Option C (Kingella kingae) is incorrect as it is a primary cause of osteoarticular infection in younger children, typically those aged between 6 months and 4 years.

Option E (Listeria monocytogenes) is incorrect as this pathogen is a key consideration in neonatal sepsis and meningitis but is not a common cause of osteomyelitis in this age group.

CORRECT ANSWER:

In a fully immunised child over three months of age presenting with suspected septic arthritis, the most common causative organism is Staphylococcus aureus.

UK national guidelines, including the British National Formulary for Children (BNFc), therefore recommend empiric intravenous anti-staphylococcal therapy. Flucloxacillin provides excellent coverage against methicillin-sensitive S. aureus (MSSA), the most probable pathogen in this age group.

Commencing treatment that targets the most likely organism is the cornerstone of effective management and antimicrobial stewardship, pending culture results and sensitivities. While local microbiology and trust guidelines should always be considered, flucloxacillin remains the standard first-line choice.

WRONG ANSWER ANALYSIS:

Option A (Amoxicillin) is incorrect because its spectrum does not reliably cover beta-lactamase producing Staphylococcus aureus.

Option B (Cefotaxime) is less appropriate as a sole agent because its anti-staphylococcal activity is weaker than flucloxacillin, although it is often added to cover Kingella kingae in younger children.

Option D (Clarithromycin) is incorrect as this macrolide antibiotic is not a first-line agent for osteoarticular infections and is typically reserved for atypical pathogens or specific allergies.

Option E (Vancomycin) is incorrect as it is a broad-spectrum agent reserved for cases with a high suspicion of methicillin-resistant S. aureus (MRSA), which is not the first-line assumption in UK community-acquired infections.

CORRECT ANSWER:

B: Septic arthritis. This patient presents with the classic triad for septic arthritis: fever, non-weight bearing, and a raised C-reactive protein.

The clinical picture of a single hot, swollen, and exquisitely painful joint, leading to a refusal to move it (pseudoparalysis), is the hallmark of a direct bacterial joint infection. The very high CRP of 210 indicates a significant inflammatory process, consistent with sepsis.

The skin pustule is the likely portal of entry for bacteria, most commonly Staphylococcus aureus, leading to bacteraemia and subsequent seeding of the highly vascular synovial membrane. This is a paediatric surgical emergency requiring prompt aspiration and washout to prevent permanent joint damage.

WRONG ANSWER ANALYSIS:

Option A (Acute osteomyelitis) is less likely as the presentation is dominated by severe joint effusion and inflammation, whereas osteomyelitis typically presents with focal bony tenderness away from the joint line.

Option C (Cellulitis with reactive arthritis) is incorrect because the fulminant presentation with systemic toxicity and a very high CRP is not in keeping with a sterile, post-infectious reactive process.

Option D (Transient synovitis) is incorrect as it is a diagnosis of exclusion, usually associated with a preceding viral illness and much milder inflammatory markers and symptoms.

Option E (Kawasaki disease) is not the primary diagnosis as this child lacks the other principal criteria required, such as conjunctivitis, rash, or mucositis.

CORRECT ANSWER:

Transient synovitis, also known as irritable hip, is the most common cause of hip pain in children in the UK. It is a benign, self-limiting inflammatory condition of the synovial membrane of the hip joint.

The pathophysiology is thought to be related to a recent viral illness, leading to a sterile joint effusion and subsequent pain and restricted movement. As the underlying inflammation is transient, the clinical course is one of complete resolution. Symptoms typically resolve fully within 7 to 10 days with simple supportive management, including rest and analgesia such as ibuprofen, making complete recovery within 1-2 weeks the expected prognosis.

WRONG ANSWER ANALYSIS:

Option A (He will likely require long-term physiotherapy) is incorrect as the condition is self-limiting and resolves completely without requiring specific rehabilitative therapy.

Option B (There is a 50% chance of recurrence) is incorrect because although recurrence is possible, the reported rate is significantly lower, typically around 4-17%.

Option D (He has a high risk of developing Perthes disease) is incorrect as the risk of developing avascular necrosis of the femoral head following transient synovitis is very low, estimated at 1-2%.

Option E (He must avoid all running for 6 months) is incorrect because prolonged activity restriction is unnecessary; activity should be reintroduced gradually as pain allows.

CORRECT ANSWER:

Staphylococcus aureus is the most frequent causative organism for acute haematogenous osteomyelitis in children older than four years. The metaphyses of long bones, such as the femur, have a rich sinusoidal blood supply with slow, turbulent flow, which predisposes this area to bacterial seeding from transient bacteraemia.

S. aureus possesses numerous virulence factors, including surface adhesins that facilitate binding to bone matrix components like collagen and fibronectin. This colonisation triggers an intense inflammatory response, leading to bone necrosis and abscess formation. Although plain radiographs are typically normal in the first 7-10 days, MRI is the imaging modality of choice due to its high sensitivity in detecting early marrow oedema and soft tissue changes.

WRONG ANSWER ANALYSIS:

Option B (Streptococcus pyogenes) is incorrect as it is a less common cause of paediatric osteomyelitis than Staphylococcus aureus.

Option C (Kingella kingae) is incorrect because it is the leading cause of osteoarticular infections in children aged 6 months to 4 years, not in a 6-year-old.

Option D (Neisseria meningitidis) is incorrect as it is a very rare cause of osteomyelitis, which would typically occur as a complication of disseminated meningococcal disease.

Option E (Haemophilus influenzae type b) is incorrect because routine childhood immunisation has made invasive disease from this organism, including osteomyelitis, extremely rare in the UK.

CORRECT ANSWER:

Option E is the correct answer because the acute inability to bear weight is a significant red flag for serious pathology. National guidelines recommend urgent referral for any child who is unable to weight bear.

This sign indicates severe pain and is a key feature distinguishing potentially urgent conditions like septic arthritis, osteomyelitis, or fractures from more benign, self-limiting causes. While transient synovitis is the most common cause of a limp, these children can typically still bear some weight. The complete refusal or inability to walk warrants immediate investigation to exclude diagnoses that could lead to permanent joint damage or other severe morbidity if treatment is delayed.

WRONG ANSWER ANALYSIS:

Option A (Limp is worse in the morning) is incorrect because morning stiffness is more characteristic of a chronic inflammatory process, such as juvenile idiopathic arthritis, which is less of an immediate emergency.

Option B (Recent upper respiratory tract infection) is incorrect as this history is very common and typically points towards more benign, post-viral causes like transient synovitis or acute myositis.

Option C (Fever of 37.4°C) is incorrect because this is a low-grade temperature and, while fever can be a sign of infection, its absence does not exclude septic arthritis and this low level is not a strong independent predictor of serious illness.

Option D (Pain reported in the knee) is incorrect because hip pathology, including serious conditions like septic arthritis or Perthes disease, commonly presents with pain referred to the knee, making it a localising but not a severity sign.

CORRECT ANSWER:

The clinical presentation is classic for a Toddler's fracture, an undisplaced spiral fracture of the tibial shaft common in children aged 9 months to 3 years. This injury results from a simple, low-energy twisting fall while walking or playing.

Crucially, these fractures are often occult on initial radiographs. Given the high index of suspicion from the history (sudden refusal to bear weight) and examination findings (a well, afebrile child with a tender tibia), the recommended management is to treat based on clinical findings. Immobilisation in an above-knee backslab or cast provides pain relief and stability. A follow-up appointment in 1-2 weeks, often with a repeat X-ray, will typically show healing callus formation, retrospectively confirming the diagnosis. This pragmatic approach avoids unnecessary further imaging or investigation in the acute phase.

WRONG ANSWER ANALYSIS:

Option A (Discharge with ibuprofen) is incorrect as analgesia alone is insufficient management for a suspected fracture and does not provide the required immobilisation for healing and pain control.

Option B (Refer for an urgent MRI scan) is incorrect because MRI is not a first-line investigation for this injury, being resource-intensive and often requiring sedation in this age group.

Option D (Admit for IV antibiotics) is incorrect as the child is afebrile and playful, making an infectious cause such as osteomyelitis or septic arthritis highly unlikely.

Option E (Send bloods for FBC and CRP) is incorrect because the absence of fever or systemic upset means inflammatory markers are not indicated as a priority and would unnecessarily delay appropriate management.

CORRECT ANSWER:

Severe pain on passive movement is the most reliable clinical sign of septic arthritis. The pathophysiology involves bacterial invasion of the synovial membrane, leading to an intense inflammatory response and purulent fluid accumulation within the joint capsule.

This purulent effusion rapidly increases intra-articular pressure, stretching the highly innervated joint capsule. Any passive movement, however slight, further stretches this inflamed and tense capsule, causing exquisite pain. The child will resist any attempted movement and will typically hold the hip in the position of maximal capsular volume to minimise this pressure: flexed, abducted, and externally rotated. This clinical finding is a key component of diagnostic aids such as the Kocher criteria for septic arthritis.

WRONG ANSWER ANALYSIS:

Option A (Hip held in extension and internal rotation) is incorrect as this position decreases the potential volume of the joint capsule, stretching it and increasing pain, whereas the position of comfort is flexion, abduction, and external rotation.

Option C (A fixed flexion deformity of the knee) is incorrect because it points towards pathology within the knee joint itself, not the hip.

Option D (Symmetrical swelling of both ankles) is incorrect as it suggests a polyarticular or systemic inflammatory process, such as juvenile idiopathic arthritis, rather than a focal septic arthritis of a single hip joint.

Option E (A positive Trendelenburg sign) is incorrect because it indicates hip abductor muscle weakness, a sign typically associated with chronic conditions like Perthes disease or developmental dysplasia of the hip, not an acute infection.

CORRECT ANSWER:

Acute osteomyelitis is the most likely diagnosis. The presentation of fever with a focal area of exquisite bony tenderness, warmth, and erythema is the classic triad for acute haematogenous osteomyelitis.

This condition involves an infection of the bone, most commonly seeded by bacteria travelling through the bloodstream. In children, the infection typically localises to the metaphysis of long bones, such as the tibia, due to the characteristics of its blood supply. The absence of joint-specific signs (like effusion or pain on passive movement) makes a primary joint pathology less probable. National guidance prioritises early recognition and treatment with intravenous antibiotics to prevent bone necrosis and chronic infection.

WRONG ANSWER ANALYSIS:

Option A (Septic arthritis of the knee) is incorrect because the examination findings are localised to the mid-tibia, with the knee joint itself being non-tender and having a full range of motion.

Option B (Cellulitis) is less likely as the exquisite tenderness is described over the bone, suggesting a deeper pathology than a superficial skin and soft tissue infection.

Option D (Ewing's sarcoma) is incorrect because its presentation is typically more insidious, often with pain and swelling over weeks or months, and less commonly associated with an acute high fever.

Option E (Stress fracture) is incorrect as this is an overuse injury that would not present with systemic signs of infection such as fever and significant inflammatory signs on the skin.

CORRECT ANSWER:

This child's presentation of a recurrent, afebrile limp with an irritable hip and normal inflammatory markers is classical for transient synovitis. This common condition is a self-limiting, non-specific inflammation of the synovial membrane of the hip joint, often following a viral illness.

National Institute for Health and Care Excellence (NICE) guidance supports a conservative approach in afebrile, systemically well children. The priority is symptomatic relief with non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, rest, and clear safety netting advice for parents to return if symptoms worsen, do not resolve within 7 days, or if the child develops a fever. This approach avoids unnecessary investigations and interventions for a benign, self-resolving condition.

WRONG ANSWER ANALYSIS:

Option A (Refer urgently to orthopaedics for aspiration) is incorrect because hip aspiration is reserved for suspected septic arthritis, which is not suggested by the afebrile state and normal inflammatory markers.

Option B (Admit for 48 hours of IV antibiotics) is incorrect as there are no clinical or biochemical signs of a bacterial infection to warrant antibiotic therapy.

Option C (Refer to paediatric rheumatology) is inappropriate as an initial step; this would be considered for multiple recurrences or atypical features, not a second typical episode.

Option E (Request an urgent MRI scan) is not indicated as a first-line investigation for suspected transient synovitis and is used when there is diagnostic uncertainty or to exclude other pathologies like Perthes disease.

CORRECT ANSWER:

The Kocher criteria are a clinical prediction rule for distinguishing septic arthritis from transient synovitis in children with an irritable hip. The four criteria are: non-weight-bearing, fever >38.5°C, Erythrocyte Sedimentation Rate >40 mm/hr, and White Cell Count >12 x10^9/L.

A C-reactive protein >20 mg/L is often used as a surrogate for ESR. This child meets three criteria (fever, non-weight-bearing, and raised WCC/CRP). The validated predictive probability of septic arthritis with three positive criteria is approximately 93%. This high likelihood mandates an urgent referral to paediatric orthopaedics for joint aspiration and washout. Septic arthritis is a surgical emergency, and delayed treatment can lead to permanent joint destruction and long-term disability.

WRONG ANSWER ANALYSIS:

Option A (< 5%) is incorrect as this probability is associated with having only one positive criterion (3%) or none at all. Option B (10-20%) is incorrect because this range does not correlate with any of the probability thresholds within the Kocher criteria algorithm. Option C (40-60%) is incorrect as a probability of 40% corresponds to having only two of the four criteria present. Option E (100%) is incorrect because while the risk is extremely high, no clinical prediction tool can provide absolute diagnostic certainty.

CORRECT ANSWER:

Refusal to bear weight is the single most powerful predictor of septic arthritis among the options provided. This clinical sign is one of the four classic Kocher criteria used to differentiate septic arthritis from transient synovitis.

The inability to weight-bear indicates a high degree of pain and inflammation within the joint capsule, which is characteristic of a bacterial infection. In septic arthritis, the inflammatory cascade triggered by pathogens leads to a rapid accumulation of purulent fluid, causing significant joint effusion and pain on any movement or loading.

While other signs overlap with transient synovitis, the complete refusal to use the limb is a significant red flag for a septic joint, which is a paediatric emergency requiring urgent surgical washout to prevent permanent joint damage.

WRONG ANSWER ANALYSIS:

Option A (Fever of 37.8°C) is incorrect as this is a low-grade fever which can be present in both conditions, whereas a temperature >38.5°C is a more specific Kocher criterion for septic arthritis.

Option B (History of a preceding viral cold) is less likely because this feature is classically associated with the reactive inflammation seen in transient synovitis.

Option D (Pain on internal rotation of the hip) is not the best indicator as hip irritability is a common finding in any inflammatory hip condition, including transient synovitis.

Option E (A mobile but irritable hip joint) is incorrect because septic arthritis typically causes such severe pain that the joint is held rigidly still in a position of comfort (pseudoparalysis), not remaining mobile.

CORRECT ANSWER:

The clinical presentation of focal bone pain, fever, and significantly raised inflammatory markers is highly suggestive of acute haematogenous osteomyelitis, despite a normal initial X-ray.

Plain radiographs are typically normal for the first 7-14 days, as demonstrable bony changes like periosteal reaction or lytic lesions are late findings. In this context, Magnetic Resonance Imaging (MRI) is the investigation of choice according to national guidelines.

MRI is highly sensitive and specific for detecting the earliest sign of osteomyelitis: bone marrow oedema. It can also accurately delineate the extent of infection, identify associated subperiosteal or soft tissue abscesses requiring surgical drainage, and differentiate from other pathologies like malignancy.

Prompt diagnosis with MRI facilitates timely and targeted antibiotic therapy, reducing the risk of complications such as chronic infection or pathological fracture.

WRONG ANSWER ANALYSIS:

Option A (Repeat X-ray in 7-10 days) is incorrect as it would lead to a significant and potentially harmful delay in diagnosis and management.

Option B (Ultrasound of the hip joint) is less appropriate because ultrasound is primarily used to detect joint effusions or superficial abscesses, and it cannot visualise bone marrow oedema to confirm osteomyelitis in the femur.

Option D (CT scan of the femur) is not the first-line choice as it is less sensitive than MRI for early marrow changes and exposes the child to significant ionising radiation.

Option E (Discharge with oral antibiotics) would be clinically unsafe as it involves treating a potentially serious infection without a definitive diagnosis, risking treatment failure and severe complications.

CORRECT ANSWER:

Septic arthritis is a paediatric emergency requiring immediate intervention to prevent irreversible joint destruction and long-term disability.

The pathophysiology involves bacterial invasion of the synovial space, leading to an intense inflammatory response that can rapidly destroy articular cartilage. National guidelines state that empirical intravenous antibiotics should be started immediately in any child with suspected septic arthritis, ideally after blood cultures and a joint aspirate have been obtained.

However, antibiotic administration should not be delayed if sampling is not immediately possible. Early antibiotic treatment is critical to sterilise the joint, control the infection, and mitigate the risk of complications such as osteomyelitis, growth plate damage, or avascular necrosis of the femoral head. The priority is treating the infection systemically while awaiting definitive surgical washout.

WRONG ANSWER ANALYSIS:

Option A (Await orthopaedic review before any medication) is incorrect because delaying antibiotics significantly increases the risk of permanent joint damage and poorer outcomes.

Option C (Administer a stat dose of oral ibuprofen) is inappropriate as the child is nil by mouth (NBM) for surgery, and oral medication is unsuitable for treating a severe systemic infection like sepsis.

Option D (Request an urgent CT scan) is incorrect because ultrasound is the first-line imaging modality to detect a joint effusion, and MRI is preferred for assessing bone involvement; CT has a limited role.

Option E (Obtain a paediatric rheumatology review) is incorrect because while rheumatological conditions can present similarly, the acute, high-inflammatory picture makes infection the primary diagnosis to treat emergently, not an inflammatory arthropathy.

CORRECT ANSWER:

This presentation is characteristic of a Toddler's fracture, a stable, undisplaced spiral or oblique fracture of the tibial shaft common in young children. The primary management goal is immobilisation for pain control and to ensure stable healing.

According to traditional and widely accepted orthopaedic principles, an above-knee cast is most appropriate. This method effectively controls the rotational forces across the fracture site, which is crucial in a spiral fracture configuration. By immobilising both the ankle and the knee, the cast prevents twisting movements of the lower leg, promoting optimal alignment and callus formation.

While some UK guidelines now suggest that very stable fractures may be managed with less rigid support, the above-knee cast remains a definitive and standard treatment to ensure stability, particularly when presented as an option in an exam context.

WRONG ANSWER ANALYSIS:

Option A (Admit for IV antibiotics) is incorrect because this is a closed fracture in an afebrile child, showing no clinical signs of osteomyelitis or infection.

Option B (Reassure and discharge, no follow-up needed) is inappropriate as all fractures require a period of immobilisation and subsequent follow-up to confirm satisfactory healing.

Option C (Urgent orthopaedic referral for surgical fixation) is incorrect as surgical intervention is reserved for significantly displaced, open, or unstable fractures, none of which are indicated here.

Option E (Refer to physiotherapy for gait training) is incorrect because physiotherapy is part of the rehabilitation phase after the cast is removed and the fracture has healed, not the acute management.

CORRECT ANSWER:

The clinical picture strongly supports a diagnosis of acute osteomyelitis. This condition arises from haematogenous seeding of bacteria, most commonly Staphylococcus aureus, into the bone.

The metaphyseal regions of long bones are particularly susceptible due to their rich but slow-flowing sinusoidal venous supply, which facilitates bacterial deposition and proliferation. The classic presentation is a triad of fever, non-articular focal bony pain, and reduced function or weight-bearing.

This child's localised tenderness and warmth over the proximal tibial metaphysis, in combination with fever and a limp, is the textbook presentation. Crucially, the adjacent knee joint is not involved, which is a key feature distinguishing it from septic arthritis.

WRONG ANSWER ANALYSIS:

Option A (Septic arthritis) is incorrect because the knee joint itself is described as cool with a full range of movement, which would be highly unlikely in a bacterial joint infection.

Option B (Transient synovitis) is less likely as it is an afebrile condition that typically affects the hip joint in a younger age group.

Option D (Osgood-Schlatter disease) is an afebrile traction apophysitis of the tibial tuberosity, not a febrile infection of the metaphysis.

Option E (Leukemia) is a less probable cause for such an acute and focal presentation, which would more typically be associated with chronic pain, night sweats, and other systemic signs.

CORRECT ANSWER:

The clinical presentation is classic for transient synovitis, a self-limiting inflammation of the synovial membrane of the hip joint, often following a recent viral illness.

The diagnosis is supported by the acute onset of a limp in a well, afebrile, weight-bearing child with normal inflammatory markers (CRP <5 mg/L). An ultrasound confirming a hip effusion is consistent with this diagnosis. According to UK practice guidelines, in the absence of red flags for septic arthritis (fever >38.5°C, non-weight bearing, raised inflammatory markers), the management is conservative. This involves symptomatic relief with non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, relative rest, and clear safety netting advice for parents to return if the child develops a fever, becomes non-weight bearing, or if symptoms do not improve within 48-72 hours.

WRONG ANSWER ANALYSIS:

Option A (Admit for IV antibiotics) is incorrect as this is the treatment for septic arthritis, which is highly unlikely given the child is afebrile with a normal CRP.

Option B (Refer to orthopaedics for joint aspiration) is an invasive procedure only indicated when there is a strong suspicion of septic arthritis to analyse synovial fluid.

Option D (Request an urgent MRI scan) is not a first-line investigation and would be reserved for cases where the diagnosis is unclear or there is suspicion of alternative pathology like osteomyelitis.

Option E (Apply skin traction and observe) has no role in the management of transient synovitis and is typically used for fractures or managing Perthes disease.

CORRECT ANSWER:

Fever greater than 38.5°C is one of the four key clinical and laboratory predictors used in the Kocher criteria to estimate the probability of septic arthritis in a limping child. This systemic sign indicates a significant inflammatory response, which is characteristic of a bacterial joint infection.

The criteria are a validated clinical prediction rule, and their utility increases with the number of positive findings. The other three criteria are: inability to bear weight on the affected limb, an Erythrocyte Sedimentation Rate (ESR) greater than 40 mm/hr (or C-Reactive Protein > 20 mg/L), and a White Cell Count (WCC) greater than 12,000 cells/mm³. The presence of three or four of these criteria carries a high probability (over 90%) of septic arthritis, mandating urgent orthopaedic consultation and joint aspiration.

WRONG ANSWER ANALYSIS:

Option B (Pain on internal rotation) is incorrect as, while it indicates hip joint irritability, it is a non-specific finding often more pronounced in transient synovitis.

Option C (Recent viral illness) is incorrect because this history is a classic feature associated with transient synovitis, the main differential diagnosis.

Option D (X-ray showing soft tissue swelling) is incorrect because early radiographic findings in septic arthritis are often normal or show non-specific changes and are not part of the diagnostic criteria.

Option E (Family history of arthritis) is incorrect as this would point towards a chronic rheumatological condition like Juvenile Idiopathic Arthritis rather than an acute septic process.

CORRECT ANSWER:

Ultrasound-guided joint aspiration is the definitive gold-standard investigation for suspected septic arthritis. Obtaining a synovial fluid sample is the most critical step as it allows for immediate microscopy (white cell count, Gram stain) and urgent culture and sensitivity testing.

This is the only method to definitively confirm the diagnosis, identify the causative organism, and guide targeted antibiotic therapy, which is vital to prevent irreversible joint damage like chondrolysis. National guidelines emphasise the urgency of joint aspiration to facilitate prompt and appropriate management. The use of ultrasound guidance increases the success rate of aspiration, confirms the presence of an effusion, and minimises procedural risks in a child.

WRONG ANSWER ANALYSIS:

Option A (Blood culture) is incorrect because while it is a crucial supportive investigation, it has a lower diagnostic yield than synovial fluid culture and a negative result does not exclude septic arthritis.

Option B (Plain X-ray of the knee) is incorrect because it is insensitive in early disease, showing only non-specific soft tissue swelling, and serves primarily to rule out bony injuries or tumours.

Option C (MRI scan of the knee) is incorrect because although highly sensitive for detecting joint effusion and inflammation, it is not specific, often requires general anaesthesia in a young child, and does not provide a sample for microbiological confirmation.

Option E (Technetium-99m bone scan) is incorrect as it is a non-specific investigation that identifies areas of inflammation and is more useful for localising occult osteomyelitis rather than confirming septic arthritis in a clinically obvious joint.

CORRECT ANSWER:

The constellation of fever, raised inflammatory markers (CRP 110), and exquisite focal metaphyseal tenderness is the classic presentation of acute haematogenous osteomyelitis.

Magnetic Resonance Imaging (MRI) with contrast is the investigation of choice and considered the gold standard for confirming the diagnosis. It is the most sensitive and specific modality in early disease, able to detect bone marrow oedema within 24-48 hours of onset.

Furthermore, MRI provides superior anatomical detail, allowing for the crucial identification of subperiosteal abscesses or other soft tissue collections that would necessitate surgical drainage in addition to intravenous antibiotics. This detailed imaging is vital for effective management planning.

WRONG ANSWER ANALYSIS:

Option A (Plain X-ray of the femur) is incorrect because radiographic changes such as periosteal reaction or lytic lesions are typically not visible for at least 7-14 days, making it unreliable for early diagnosis.

Option B (Ultrasound of the knee joint) is less appropriate as it is primarily used to detect joint effusions or superficial fluid collections, and it cannot visualise bone marrow oedema; the examination findings here point to a bone rather than a joint pathology.

Option D (CT scan of the femur) is not the most definitive modality as it is less sensitive than MRI for early marrow changes and soft tissue infection, while exposing the child to significant ionising radiation.

Option E (Technetium-99m bone scan) is incorrect because while sensitive, it lacks the spatial resolution of MRI and is less specific, making it difficult to distinguish infection from other causes of increased bone turnover.

CORRECT ANSWER:

This child's presentation is classic for a Toddler's Fracture, which is an undisplaced spiral or oblique fracture of the distal tibia. The mechanism is typically a low-energy torsional force, such as that from a simple fall or twisting motion while playing, which aligns with the history of climbing.

In a well, afebrile child with a sudden refusal to bear weight and localised bony tenderness, fracture is the primary diagnosis to exclude. National guidelines recommend plain radiography as the first-line imaging modality for suspected fractures in children. An X-ray of the tibia and fibula is a rapid, accessible, and definitive investigation to confirm the diagnosis and guide management, which usually involves immobilisation in a cast.

WRONG ANSWER ANALYSIS:

Option A (FBC, CRP and blood culture) is incorrect because these investigations are for suspected infection, and this child is afebrile and systemically well, making septic arthritis or osteomyelitis much less likely.

Option B (MRI scan of the left leg) is not the appropriate initial investigation as it is more resource-intensive and typically reserved for diagnostic uncertainty, such as suspicion of osteomyelitis with normal X-rays.

Option C (Ultrasound of the left hip) is incorrect because the clinical signs are clearly localised to the lower leg, whereas an ultrasound would be used to investigate hip pathology like an effusion.

Option E (Reassure and discharge with analgesia) is inappropriate as it would risk missing a definite fracture, potentially leading to delayed healing, displacement, and prolonged pain.

CORRECT ANSWER:

The clinical presentation of high fever, pseudoparalysis of a limb, and a warm, swollen joint held in a fixed position is septic arthritis until proven otherwise. This is a paediatric surgical emergency.

The bacterial infection and subsequent inflammatory response can rapidly destroy the articular cartilage of the hip, leading to irreversible long-term damage and disability. According to all national guidelines, the absolute priority is urgent surgical intervention for joint aspiration, washout, and antibiotic administration. Therefore, the most appropriate immediate step is to make the child nil by mouth (NBM) in preparation for theatre and secure an emergency referral to the on-call orthopaedic team.

WRONG ANSWER ANALYSIS:

Option A (Administer oral ibuprofen and review in 24 hours) is incorrect because it fails to address the underlying infection and dangerously delays the time-critical surgical management required.

Option B (Request an outpatient ultrasound of the hip) is incorrect as the need for treatment is emergent, and an outpatient appointment would cause an unacceptable delay.

Option D (Perform a full septic screen including lumbar puncture) is incorrect because while blood tests are required, the priority is the surgical management of the hip, and a lumbar puncture is not indicated without signs of meningitis.

Option E (Discharge with safety netting advice for viral illness) is incorrect as it misses the clear red flag signs of a focal bacterial infection requiring immediate hospital admission.

CORRECT ANSWER:

The diagnosis is transient synovitis, a self-limiting inflammation of the hip's synovial membrane. This case is a classic presentation.

The key features are the preceding coryzal illness, suggesting a post-viral reactive process, and the child's afebrile and systemically well state. The limp is acute, but the child remains weight-bearing. Examination reveals pain only at the extremes of hip movement, particularly internal rotation, which is characteristic.

The normal inflammatory markers (WCC and CRP) are crucial in distinguishing this benign condition from more severe pathologies like septic arthritis. The pathophysiology involves a temporary, non-specific inflammation and effusion in the hip joint, which typically resolves with conservative management within one to two weeks.

WRONG ANSWER ANALYSIS:

Option A (Septic arthritis) is incorrect because the child is afebrile and systemically well, with inflammatory markers that are not significantly raised.

Option C (Osteomyelitis) is less likely due to the absence of high fever, focal bony tenderness on examination, and a significantly elevated CRP.

Option D (Perthes disease) is unlikely as it typically presents with a more insidious onset of a painless or mildly painful limp over weeks or months, not acutely over two days.

Option E (Toddler's fracture) is less probable as this typically involves a non-displaced spiral fracture of the tibia in a younger child, and the clinical findings point strongly towards hip pathology.