(Choices A and C) Bacterial arthritis typically presents acutely with fever and inability to bear weight as well as pain, swelling, erythema, and warmth of the joint. Osteomyelitis typically affects the metaphyses of long bones (eg, humerus, femur) and classically presents with fever, point tenderness, and localized edema. This patient is afebrile, appears well, and has chronic pain, making bacterial infection unlikely.
(Choice B) Untreated developmental dysplasia can lead to limp and hip pain in childhood or adolescence. Initial radiographs show a dysplastic or dislocated hip. In addition, physical examination typically reveals a leg-length discrepancy (ie, shortening of the affected extremity), which is not seen in this patient.
(Choices A and C) Bacterial arthritis typically presents acutely with fever and inability to bear weight as well as pain, swelling, erythema, and warmth of the joint. Osteomyelitis typically affects the metaphyses of long bones (eg, humerus, femur) and classically presents with fever, point tenderness, and localized edema. This patient is afebrile, appears well, and has chronic pain, making bacterial infection unlikely.
Explanation
This patient most likely has Legg-Calvé-Perthes disease (LCP), or idiopathic osteonecrosis (avascular necrosis) of the femoral head. LCP classically affects boys age 3-12, with peak incidence at age 6.
Patients typically have an antalgic gait (avoids weight bearing on the affected side due to pain) and dull, chronic lower extremity pain of insidious onset. The pain may affect the hip directly or present as referred thigh or knee pain, as in this patient. Diagnosis requires a high index of suspicion as initial x-rays may be normal. Persistent symptoms should prompt repeat imaging, which in later stages typically shows sclerosis of the femoral head with flattening and fragmentation. As the disease progresses, examination may reveal limited internal rotation and abduction of the hip. Proximal thigh atrophy and Trendelenburg sign may also be present.
Treatment is aimed at maintaining the femoral head within the acetabulum by avoiding weight-bearing activities and by splinting or surgery.
Educational objective: Legg-Calvé-Perthes disease, or avascular osteonecrosis of the femoral head, typically presents in boys age 3-12 with insidious-onset hip or (referred) knee pain and an antalgic gait. X-rays may be normal in early disease but demonstrate abnormalities (eg, femoral head flattening, fragmentation, sclerosis) with chronic symptoms.
(Choice E) Slipped capital femoral epiphysis also presents with limp and insidious hip pain. Patients are typically adolescent and obese, neither of which is true in this patient. In addition, x-ray shows posterior displacement of the femoral head, unlike the normal x-rays in this patient.
(Choice F) Transient synovitis also presents with hip or knee pain and limp; however, symptoms typically develop after a viral infection and resolve within 4 weeks. This patient has had symptoms for 2 months and more likely has LCP.
