Evaluation of the unstable total hip arthroplasty.

Despite advances in total hip arthroplasty, dislocation persists as a troublesome complication for orthopaedic surgeons to manage, second only to prosthetic loosening as a cause of revision. Although this complication has received considerable attention, evaluation and treatment of the unstable total hip arthroplasty remain poorly understood. Therefore, it is important to evaluate such factors as underlying patient comorbidities, the direction of dislocation, soft-tissue tension, surgical technique, implant design, and component position. For recurrent hip instability, a careful history to determine the mechanism of dislocation is necessary, and a review of preoperative imaging studies can help clarify whether gross component malpositioning is present. Examination under anesthesia and intraoperative inspection are also important. Taking the hip through a full range of motion while directly visualizing the anatomy can help diagnose component-to-component impingement, inadequate offset soft-tissue tension, extra-articular impingement, and other possible contributing factors. Even when a seemingly obvious cause of dislocation, such as component malposition, is diagnosed, surgical results have been somewhat disappointing. Therefore, surgical planning should include all possible revision options, and the temptation to find the quick fix should be resisted. Patients should be extensively counseled regarding realistic expectations both before primary hip arthroplasty and in the face of a revision surgery for recurrent dislocations because long-term results are less than optimal.