The Unstable Total Hip Replacement

Dislocation of a THA is defined by the loss of contact between the femoral headand acetabular component that requires intervention to relocate the joint. Instabilityafter total hip arthroplasty traditionally occurred between %1 and %3. The risk ofdislocation after revision surgery is clearly increased greatly ranging from %5 to %20.Numerous factors have been associated with dislocation including patient variablessuch as age, gender, body weight and height, early postoperative compliance, softtissue integrity, and neurologic conditions such as poor proprioception, as well assurgical factors such as implant design, surgical approach, failure to restore properhip mechanics and soft tissue restraints. A thorough understanding of the timing,mechanism of dislocation, and direction of dislocation is necessary in formulatingan approach toward treatment. The radiographic evaluation should evaluate hipmechanics including adequacy of leg lengths, component orientation, and restorationof offset in the frontal and sagittal planes.