Limping Child Approach
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Direct answer
The limping child approach is an age-based method for finding why a child walks abnormally, with septic arthritis as the diagnosis never to miss. In children aged about three to ten years, transient synovitis is the commonest benign cause, while Perthes disease and slipped capital femoral epiphysis cover most of the rest. Fever, refusal to bear weight and raised inflammatory markers call for urgent hip aspiration and IV antibiotics.
What you must remember
- Most urgent cause: septic arthritis, where a febrile child who will not bear weight needs same-day assessment and aspiration of any effusion.
- Kocher criteria: fever above 38.5°C, refusal to bear weight, ESR above 40 mm per hour and white cell count above 12,000 per cubic mm; more criteria present mean higher risk.
- Transient synovitis: the commonest benign cause, usually aged 3 to 10 years, often after a viral illness, with mild or absent fever and a diagnosis of exclusion.
- Perthes disease: avascular necrosis of the femoral head in boys aged about 4 to 10 years, where the early radiograph may look normal.
- Slipped capital femoral epiphysis: adolescents, typically obese boys aged about 10 to 16 years, presenting with hip pain or referred knee pain.
- Infant limp: developmental dysplasia of the hip and septic arthritis dominate below about three years of age.
- Red flag for malignancy: night pain, weight loss, persistent fever or bone pain with pallor should prompt a full blood count and imaging for leukaemia or bone tumour.
Working through the limp in a fixed sequence
A limp is a symptom, not a diagnosis, so the history comes before any detailed hip examination. The sequence below removes the emergencies first, leaving self-limiting causes for last.
- Establish the timeline: ask whether the limp came on over hours or weeks, and whether there was trauma, a recent viral illness or night pain.
- Check for systemic illness: a child with fever, a toxic look or inability to bear weight needs blood tests and urgent senior review.
- Examine the hip fully: measure internal rotation and abduction, look for pain on passive movement, and compare leg lengths with the child lying supine.
- Order targeted investigations: send a blood count, ESR and CRP, then arrange a hip ultrasound for effusion and a pelvic radiograph with a frog-leg lateral view.
- Aspirate when septic arthritis is likely: a significant effusion in a febrile child needs aspiration for culture and prompt IV antibiotics, even when the radiograph looks normal.
Transient synovitis is reached only after the emergencies are excluded. A normal radiograph in the first week does not rule out septic arthritis or early Perthes disease, so clinical trend and repeat imaging matter.
Where the exam tries to catch you
Limp questions usually turn on the child's age and whether fever is present.
- Trap: diagnosing transient synovitis in a febrile child who cannot bear weight Correct: this is septic arthritis until proven otherwise, and the child needs aspiration and IV antibiotics.
- Trap: reassuring the family because the radiograph is normal Correct: early septic arthritis and Perthes disease can show normal films, so ultrasound, blood tests and MRI guide the decision.
- Trap: attributing knee pain in an obese adolescent to the knee joint Correct: the pain is often referred from the hip, so slipped capital femoral epiphysis must be excluded by hip imaging.
- Trap: labelling a persistent limp as a sprain without imaging Correct: a limp that persists needs assessment for developmental dysplasia, osteomyelitis and tumours.
Frequently asked questions
Which is the most important diagnosis to exclude in a limping child?
Septic arthritis is the most important diagnosis to exclude in a limping child because joint destruction can begin within days. A febrile child who refuses to bear weight needs urgent blood tests, hip ultrasound for effusion and aspiration, with IV antibiotics started promptly.
What are the Kocher criteria for septic arthritis?
The Kocher criteria for septic arthritis are fever above 38.5°C, refusal to bear weight, ESR above 40 mm per hour and white cell count above 12,000 per cubic mm. The more of these criteria a child has, the higher the probability of septic arthritis, so a child with all four needs urgent joint aspiration.
How does Perthes disease present in a school-age boy?
Perthes disease in a school-age boy presents with a painless or mild limp, knee or groin pain and loss of hip abduction and internal rotation. The early radiograph can be normal, so MRI or a repeat radiograph is used to confirm avascular necrosis of the femoral head.
When should a limp in a young child prompt investigation for a tumour?
A limp in a young child should prompt investigation for a tumour when there is night pain, weight loss, persistent fever, bone tenderness at a non-joint site or abnormal blood counts. Blood counts and imaging of the affected bone help identify leukaemia or a bone tumour, which should not be dismissed as a simple sprain.