What are the causes of hip pain in childhood?
• Transient synovitis, malignancy—local, benign (e.g., osteoid osteoma), malignant (e.g., Ewing sarcoma), generalized, leukemia, neuroblastoma.
• Septic arthritis.
• Avascular necrosis (Legg–Calvé–Perthes disease).
• Slipped capital femoral epiphysis (SCFE).
• Protrusio acetabuli.
• Osteomyelitis (femur, pelvis).
• JIA (including enthesitis-related arthritis [ERA]/juvenile spondyloarthropathy [JAS]).
• Rheumatic fever/reactive arthritis.
Pearl: Arthritis of the hip joint is rare at the onset of oligoarticular JIA . Onset of apparent arthritis in the hip in a young child should be considered first to be a septic process. The presence of (1) fever (≥38.5°C); (2) WBC count > 12,000/μL; (3) ESR ≥ 40mm/hour; (4) C-reactive protein ≥ 20 mg/L; and (5) inability to bear weight predicts that septic arthritis is more likely than transient synovitis of the hip. Without these systemic symptoms, congenital dislocation should be considered. Transient synovitis of the hip may cause very severe pain, but the process is self-limited, lasting one to a few weeks, and all laboratory and radiologic studies are normal. In the older child and adolescent, avascular necrosis (Legg–Calvé–Perthes disease) and SCFE should be considered. In older boys, ERA/JAS may present with unilateral or bilateral hip involvement, although distal joints are affected more commonly than proximal joints. Be aware that hip pain, while typically anterior groin in location, may rarely be referred to the knee.