Abstract
Introduction
Recurrent dislocation following total hip arthroplasty (THA) is a complex, multifactorial problem that has been shown to be the most common indication for revision THA. The purpose of this study was to classify causes of instability and evaluate outcomes based on an algorithmic approach to treatment.
Methods
Two surgeons performed 75 consecutive revisions for instability. Patients had a mean of 2 (range, 0 to 6) prior operative attempts to resolve their instability. Subjects were divided into 6 types based on etiology of instability: I) malposition of the acetabular component, II) malposition of the femoral component, III) abductor deficiency, IV) impingement, V) late wear, or VI) unclear etiology. Types I/II were treated with revision of the malpositioned component, Type III/VI with constrained liner, Type IV by removing sources of impingement and Type V with liner change. Large (>36mm) femoral heads were used routinely.
Results
The causes of instability were Type I: 25 (33%); Type II: 8 (10%); Type III: 28 (37%); Type IV: 7 (9%); Type V: 5 (7%); Type VI: 3 (4%). At a mean of 32.5 months (Range, 24 to 79) 12 patients re-dislocated (15.6%). Among these 12 failures 8 (75%) were in patients with abductor insufficiency (Type III) treated with a constrained liner.
Conclusions
The most common causes of instability were cup malposition and abductor insufficiency. Our treatment protocol had an 84.4% success rate. The highest risk of failure was in patients with abductor insufficiency with revision for other etiologies having a success rate of 92%.
