Research synthesis of recommended acetabular cup orientations for total hip arthroplasty

Total Hip Arthroplasty (THA) is regarded as one of the most successful surgical procedures of modern times yet continues to be associated with a small but significant complication rate. Many early failures may be associated with poor component positioning with, in particular, acetabular component orientation dependent on the subjective judgement of the surgeon. In this paper, we compare the manufacturers’ instructions on acetabular cup orientation with the literature-based recommended safety zones, by transforming them onto a single, clinically-relevant framework in which the different reference systems, safety guidelines and current instrumentation surgical techniques can be evaluated. The observed limited consensus between reflects ongoing uncertainty regarding the optimum acetabular component positioning that is probably responsible for a significant number of hip dislocations and early revisions. Our analysis suggests a new safety zone - the Strathclyde Safety Zone, SSZ (30° - 55° inclination and 5° - 30° anteversion) - defined in the operative reference frame, that encompasses other safety zones and which, incidentally, holds the majority of manufacturers’ guideline positions.