Investigation of the Unstable Total Hip Arthroplasty.

The investigation of recurrent instability after total hip arthroplasty requires a thorough history and physical examination focused on characterizing the dislocation events and the patient factors that contribute to instability. Radiographic studies include plain radiographs, in particular a cross-table lateral, and computed tomography to accurately assess the implant orientation relative to the patient's native anatomy. More advanced imaging such as magnetic resonance imaging may be useful to assess abductor tendon integrity. A classification system, based on etiology of recurrent instability, is available and helpful to guide treatment strategy. Finally, emerging research has debunked the previous characterization of an acetabular "safe zone" and further identified lumbar spine disease and surgical fusion as a significant risk factor for recurrent instability. Current and future research efforts target radiographic assessment of lumbopelvic alignment in diagnosis, treatment, and prevention of recurrent total hip arthroplasty instability.