Limping Child

Differential Diagnosis and Management

The likely cause of a limp is highly dependent on the child’s age and the presence of red flags.

• Transient Synovitis (“Irritable Hip”) 

  • Presentation: The most common cause of a limp in children aged 3-8 years. It’s a diagnosis of exclusion. The child is otherwise well, with a history of a recent viral illness. The limp is usually of short duration and the child can still weight-bear. Pain is localised to the hip, but can be referred to the knee.

  • Management: No investigations are needed if there are no red flags. Treatment is supportive with rest and simple analgesia (paracetamol, ibuprofen). Crucially, the child must be reviewed in 48-72 hours to ensure symptoms are improving and to rule out other conditions.

• Septic Arthritis (Sepsis of the joint)

  • Presentation: A medical and orthopaedic emergency that can rapidly destroy a joint. The child is usually systemically unwell with a fever and is often unwilling to weight-bear. The affected joint is typically swollen, red, hot, and exquisitely painful to move.

  • Management: Urgent joint aspiration and blood cultures are required before antibiotics are given if the child is clinically stable. If the child is systemically unwell, antibiotics must not be delayed. The child requires urgent orthopaedic review and admission to hospital.

• Toddler’s Fracture

  • Presentation: A spiral fracture of the tibia, common in children aged 9 months to 3 years. It’s often unwitnessed. The child may refuse to weight-bear and can have a subtle limp. Examination may reveal tenderness over the tibia.

  • Management: An X-ray of the tibia is needed.

• Perthes Disease

  • Presentation: Avascular necrosis of the femoral head, typically affecting boys aged 4-10 years. It causes a painless or painful limp. X-ray shows an irregular, flattened femoral head.

  • Management: Requires a referral to a paediatric orthopaedic team.

• Slipped Upper Femoral Epiphysis (SUFE)

  • Presentation: The head of the femur slips at the growth plate. It’s an important diagnosis in obese, peripubertal children (especially boys) aged 10-15 years. The affected leg is often externally rotated, and hip internal rotation is severely restricted.

  • Management: An urgent paediatric orthopaedic review is needed. Diagnosis requires an AP and frog-leg lateral view of the hip X-ray.

• Other Serious Diagnoses:

  • Osteomyelitis: A bone infection that can mimic septic arthritis.

  • Malignancy: A diagnosis of exclusion. Consider leukaemia or bone tumours in a child with night pain, weight loss, or constitutional symptoms.

  • Juvenile Idiopathic Arthritis (JIA): The limp is often chronic and worse in the morning.

  • Henoch-Schönlein Purpura (HSP): A vasculitis that can cause a painful limp and joint swelling, in addition to the characteristic purpuric rash.

Assessing a child with a limp is a common but complex task. The key nuance is that a child’s gait can be affected by a huge range of issues, from something as trivial as a splinter to life-threatening conditions. The biggest pitfall is failing to identify the red flags that point to a serious diagnosis.

Nuances of Assessment

• Age Matters: The differential diagnosis changes significantly with age. For a 2-year-old, a toddler’s fracture is a common cause, whereas in an obese 13-year-old, you must rule out a slipped upper femoral epiphysis (SUFE).

• The “Referred Pain” Trap: Children, particularly younger ones, are often unable to accurately localise their pain. Pain originating in the hip is frequently referred to the knee or thigh. A diligent clinician must always examine the hip joint, even if the child only complains of knee pain.

• Subtle Signs: A sick child may not exhibit obvious signs of infection. In a septic joint, the initial signs might just be a subtle reluctance to move the limb or a restriction in the hip’s internal rotation. Don’t be fooled by a normal-looking joint or a lack of fever—both can be late signs.

• The Power of Observation: Much can be learned before a formal examination begins. Watch the child as they enter the room. Do they refuse to weight-bear? Is their gait antalgic? Does their leg seem to be externally rotated? These visual clues can be more valuable than a verbal history.

Common Pitfalls

• Dismissing Symptoms Due to Trauma History: A history of a minor fall is a frequent distraction. A child with a serious underlying condition (e.g., bone tumour or a pathological fracture) may be more prone to falling, and the fall is just a “red herring.” Always consider what lies beneath.

• Misinterpreting “Irritable Hip”: Transient synovitis is a diagnosis of exclusion. The biggest mistake is to assume a limp is just a simple “irritable hip” without properly excluding a septic joint. While both may present with a limp after a viral illness, a child with septic arthritis is typically systemically unwell with a fever and is unwilling to weight-bear. If there are any red flags, a septic joint must be presumed until proven otherwise.

• Reassuring a Family Based on Normal X-rays: An initial X-ray can be normal in early osteomyelitis or septic arthritis. These conditions can be present without visible changes on a radiograph, and a normal X-ray does not rule them out. Clinical suspicion is paramount.

• Failing to Get a Full Picture: Don’t just focus on the lower limb. A limp can be caused by conditions elsewhere, such as testicular torsion (referred pain to the groin), a spinal discitis, or even a hernia. A thorough physical exam, including the abdomen and back, is crucial.

• Over-reliance on Investigations: While inflammatory markers (CRP) and blood tests can be helpful, they are not foolproof. They may be normal in the early stages of a serious infection. The decision to investigate further or admit a child should be based on a combination of the clinical picture, risk factors, and the presence of any red flags.