Piriformis preservation in total hip arthroplasty: do we have a new concept? An update on anatomy, function and clinical outcomes

The piriformis muscle (PM) is important for posture and preventing falls. It is a key landmark for hip surgery. The PM function is reported to be increasingly important for improving total hip arthroplasty (THA) outcomes and reducing complications. This scoping review aims to map and summarize the literature on the anatomy and function of the PM and the outcomes of clinical studies on THA preserving the PM to improve readers' understanding and identify areas for further research. A scoping review following the PRISMA guidelines was conducted using PubMed and Scopus from their inception until June 2023. We used the search term 'piriformis' or 'PM' to include all PM-related studies. Two independent reviewers screened abstracts and full texts to select key aspects of PM anatomy and function and the main clinical THA studies reporting outcomes on PM preservation. Fifty-seven studies published between 1980 and 2023 met our inclusion criteria. During hip surgery, the PM anatomy, including its origin and insertion, muscle belly, and relation to other short hip rotators and the sciatic nerve, can vary greatly, making it difficult to recognize. The current literature on PM-preserving THA and hemiarthroplasty clinical studies is limited. It suggests potential benefits in terms of hip stability, dislocation risk, and functional outcomes compared to no PM preservation in short-term follow-up. Identifying and preserving the PM during hip surgery may be difficult due to its variable anatomy and its relation to surrounding structures. Although the literature supporting PM preservation potentially indicates better outcomes, further high-level research studies are needed.