Delayed diagnosis of hip dislocation in a young child.

Case A 4-year-old girl injured her left leg while tobogganing. She complained of immediate pain in her left knee and refused to bear weight through her left lower extremity. Her family brought her to the local emergency department where radiographs of the left knee were obtained; radiographic findings of the knee were normal (Figure 1). It was believed that the patient had a soft tissue injury to the knee, and she was discharged home. The patient continued to complain of discomfort in the left knee and refused to bear weight. The family returned to the emergency department 10 days after the initial injury for re-assessment. Bilateral knee radiographic findings were again normal. The diagnosis of a soft tissue injury to the knee remained. However, for a further 4 weeks, the patient continued to describe knee pain and would not bear weight. At follow-up 6 weeks after injury, a radiograph of the pelvis was obtained and revealed a dislocation of the left hip (Figure 2). An urgent referral was made to the pediatric orthopedic surgeon on call. The pediatric orthopedic team’s assessment revealed the following: the patient had limited abduction of the left hip to 30°, a positive Galeazzi sign (unequal knee heights suggesting unilateral hip dislocation), and normal neurologic examination findings for the left lower extremity (Figures 3 and 4). A magnetic resonance imaging scan of the pelvis was performed immediately to assess the soft tissues around the dislocated hip and to assist with preoperative planning. It revealed a posterior and superolateral left hip dislocation with the femoral head protruding through the posterior hip capsule. There was no evidence of osteonecrosis. The patient was taken to the operating room for urgent management of her dislocated hip. Under general anesthesia, a closed reduction failed. An open reduction was performed using a posterior approach. The femoral head was buttonholed through the posterior hip capsule (Figure 5). The joint was filled with thick fibrous tissue, and a small osteochondral defect was found in the posterior acetabulum. The hip was reduced. An adductor tenotomy was performed to help maintain the reduction, and a hip spica cast was applied (Figure 6). The patient was discharged home when she was comfortable. She remained in the spica cast for 5 weeks. At her 9-month follow-up appointment, the patient had full range of motion in her hips and was walking well. Radiographic findings completed at follow-up revealed medial joint space widening and flattening of the epiphysis without fragmentation, similar to early Legg-Calvé-Perthes disease (Figure 7). EDITOR’S KEY POINTS • A high index of suspicion for hip dislocation is necessary in children who present with knee pain after low-energy trauma.