Figure. Anteroposterior radiograph of the right hip.
An 8-year-old boy presents to the emergency department with right hip pain that began 2 days earlier. The boy’s mother reports that the child has not experienced any recent injury. The boy is unable to put any weight on his right leg and has severe pain with any passive motion of the hip. He is afebrile, and his erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level are both within normal limits. However, his white blood cell (WBC) count is elevated slightly. The patient’s mother states that he is healthy aside from having experienced an upper respiratory illness 1 week ago. Anteroposterior radiograph of the right hip is obtained (Figure).
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Pediatric hip pain is a challenging symptom that may present in many practice settings. The differential diagnosis in this patient’s case includes septic arthritis and transient synovitis.1,2
Transient synovitis of the hip often presents with little to no elevation in WBC and normal ESR and CRP laboratory results. The etiology of transient synovitis is unknown, but the condition usually presents in a patient with a recent history of upper respiratory infection. Hip pain in pediatric patients who present with fever and elevated WBC, ESR, and CRP values is more commonly associated with septic arthritis.
CRP is the most predictable laboratory test in the differential diagnosis of septic arthritis. With acute infection, CRP levels will increase within 6 hours of an inflammatory response and will peak at 2 days. A CRP level >20 mg/L is highly predictive of septic arthritis.1,2
Radiographs of the hip should always be obtained in this setting to rule out bony injury or deformity. For example, Legg-Calve-Perthes disease is an idiopathic avascular necrosis of the femoral epiphysis that most often occurs in children between the ages of 4 and 8 years. Legg-Calve-Perthes disease will often present with irregularities of the femoral head on radiographic examination. A slipped capital femoral epiphysis, on the other hand, is a slippage of the metaphysis relative to the epiphysis and most commonly occurs in obese boys of approximately 13 years of age.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
1. Arkader A, Brusalis C, Warner WC Jr, Conway JH, Noonan K. Update in pediatric musculoskeletal infections: when it is, when it isn’t, and what to do. J Am Acad Orthop Surg. 2016;24(9):e112-e121.
2. Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999;81(12):1662-1670.