Atraumatic Posterior Hip Dislocation following Short Femoral Nail for Intertrochanteric Fracture Treated by Dual Mobility System in Total Hip Arthroplasty: A Case Report

INTRODUCTION: Atraumatic hip dislocation after short femoral nail (SFN) fixation for an intertrochanteric fracture is extremely rare. CASE REPORT: An 84-year-old woman presented with an atraumatic posterior hip dislocation that occurred 8 years after SFN fixation for an intertrochanteric hip fracture. She experienced an acute-onset left hip pain when standing up from a sitting position while bathing at a day care facility. We performed total hip arthroplasty (THA) with a dual mobility system. During the post-operative THA evaluation, the combined anteversion angle was within the optimum range of 57. However, the dislocation recurred after the THA. During the revision THA, a dual mobility system was used to moderately extend the stem neck. Measures were adopted to strain the posterior soft tissues of the hip joint. We speculated that the posterior hip joint capsule ruptured because the support of the posterior hip joint was weak after the intertrochanteric hip fracture. At the final follow-up visit at 6 months after the operation, the hip joint pain had disappeared, and her activities of daily living recovered to almost the same level as her preinjury activities. CONCLUSIONS: We should consider the lack of support of posterior soft tissues as a cause of this atraumatic posterior hip dislocation following intertrochanteric fracture fixation.