The dislocator, early and late: the 3 am phone call.

Hip dislocation is one of the most common causes of patient and surgeon dissatisfaction following hip replacement. To correctly treat dislocation, the causes must first be understood. Patient factors include age older than 70 years, medical comorbidities, female sex, musculoligamentous laxity, revision surgery, issues with the abductors and trochanter, and lack of education. Issues related to the surgeon and technique are surgical volume and experience, surgical approach and repair, adequate restoration of femoral offset and leg length, correct component position, and avoidance of soft tissue or bony impingement. Chief among implant-related factors is the design of the head and neck region. Is the femoral head diameter sufficient, and, in concert with the prosthetic neck, is there an adequate head-neck ratio? Skirts on longer neck lengths greatly reduce the head-neck ratio and should be avoided if possible. There must be available offset choices to restore soft tissue tension. Lipped liners aid in gaining stability, yet may result in impingement and dislocation if improperly placed. Late dislocation may result from polyethylene wear, soft tissue destruction, trochanteric or abductor disruption and weakness, or infection. Understanding the causes of hip dislocation allow prevention in a majority of instances. Proper preoperative planning includes the identification of high-offset patients in whom inadequate restoration of offset will reduce soft tissue tension and abductor efficiency. Component position must be accurate to achieve stability without impingement. Finally, patient education cannot be overemphasized, as most dislocations occur early and are preventable with proper instructions.