Dislocation of Hip - Epidemiology

Epidemiology

Acquired hip dislocation has the highest incidence rate immediately after hip replacement surgery and continues to have a high level for possibility of incidence throughout the first three months following the surgery. Following a primary total hip replacement surgery, 3.9% of patients experience hip dislocation during the twenty-six postoperative weeks. Following a revision total hip replacement surgery, approximately 14.4% of patients experience hip dislocation during the twenty-six postoperative weeks. The incidence of hip dislocation following hip replacement surgery greatly depends on patient, surgical and hip implant factors. Preoperative hip range is the most likely the most influential contribution as to whether a hip is able to remain stable or not. Because hip stability greatly depends on hip range of motion it is crucial for a hip’s postoperative range of motion to fall within a certain range in order to ensure maximum stability.

Following partial or total hip replacement surgery, patients with 115 degrees or greater of combined preoperative adduction, internal rotation, and adduction as well as a posterior approach experienced hip dislocation at a considerably higher frequency than patients who had less than 115 degrees of combined hip range of motion. In addition to the degrees of range of motion a patient possesses post surgery; size of the femoral head is another large contributing factor to the stability of the hip. High preoperative motion in combination with a posterior approach and femoral head size that is less than 32 mm had the highest hip dislocation rate. In general, the larger the head of the femur post surgery, the less likely a patient is to experience dislocation. This is because during the replacement surgery, a patient’s “ball and socket” of the femur head and hip socket are changed and no longer fit together in the perfect way they did prior to surgery. When a femur head is smaller than 32 mm post surgery, the looser the “ball” femur head fits inside the hip “socket”, therefore increasing the likelihood for the femur to slip and slide out of the socket, causing hip dislocation.