Abstract
Larger diameter femoral heads and improved operative approaches and soft tissue repair/closure have somewhat reduced the incidence of recurrent instability after total hip arthroplasty (THA). Nevertheless, hip instability remains one of the most common reasons for reoperation after THA, and accounts for roughly a quarter of hip revisions in the United States in Medicare patients. The prevalence of instability after THA varies widely, from 0.3% to 15%. Surgeons have come to understand that hip instability can be caused by implant malposition, impingement, and inadequate soft tissue tension or integrity. While the cumulative risk of instability is acceptable at approximately 2.8% with transtrochanteric approaches, this is based upon the trochanter actually healing (and often being advanced). On the other hand, trochanteric nonunion and proximal migration have been noted by many, and this frequently results in catastrophic instability. Moreover, and importantly, abductor insufficiency is one the most difficult causes of hip instability to solve. Woo and Morrey reported a 17.6% instability rate when trochanteric nonunion occurred with 1 cm proximal trochanteric migration. Alternatively, the contemporary incidence of instability with the posterolateral or anterolateral approaches, and an adequate soft tissue repair, is approximately 1–2%.
