Optimizing Acetabular Component Bone Ingrowth:The Wedge-Fit Bone Preparation Method

We investigate the efficacy of a modified acetabular bone-preparation technique in reducing the incidence of two clinical problemsidentified in hip resurfacing arthroplasty. The first issue is failure due to lack of bone ingrowth into the acetabular component.The second is a newly recognized phenomenon of early cup shift. We hypothesize that these issues might be resolved by using a“wedge-fit method”, in which the component wedges into the peripheral acetabular bone rather than bottoming out and potentiallytoggling on the apex of the cup. Prior to November 2011, all acetabula were reamed 1 mm under and prepared with a press-fit of theporous coated acetabular component. After November 2011, we adjusted reaming by bone density. In “soft bone” (T-score<-1.0),we underreamed acetabula by 1 mm less than the outer diameter of the cup, as was previously done in all cases. For T-scores greaterthan -1.0, we reamed line-to-line. Additionally, we began performing an “apex relief” starting June 2012 in all cases by removing 2mm of apex bone with a small reamer after using the largest reamer. Failure of acetabular ingrowth occurred in 0.5% of cases beforethe wedge-fit method and<0.1% after. Rate of cup shift was reduced from 1.1% to 0.4%. The rate of unexplained pain between 2 and4 years postoperatively also declined significantly from 2.6% to 1.3%. Our evidence suggests that wedge-fit acetabular preparationimproves initial implant stability, leading to fewer cases of early cup shift, unexplained pain, and acetabular ingrowth failure