Anatomical Mechanisms of Femoroacetabular Impingement and Its Role in the Progression to Hip Osteoarthritis: A Systematic Review.

Femoroacetabular impingement (FAI) causes hip pain because of unusual bone shapes at the area where the femur connects to the hip (cam-type) or at the hip socket (pincer-type). Due to the rarity of hip osteoarthritis, people in India often overlook FAI. Significant knowledge gaps exist in the underlying pathophysiology of FAI, impacting its progression. This study aims to look at the shape changes in the femoral head-neck junction in FAI and how these changes relate to the development of hip joint osteoarthritis. We chose original reviews, book chapters, and controlled trials written in English about the causes, symptoms, and progression of FAI that were published between January 2015 and December 2024 from the PubMed/Medline and Scopus databases. Case reports, series, editorials, commentaries, abstracts, and preprints were excluded. The risk of bias in systematic reviews (ROBIS) tool was used to assess the risk of bias in selected studies, and a standardized data extraction checklist was used to obtain pertinent data for synthesis. This research protocol was prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO) under registration ID CRD42025638992. A PubMed and Medline search using the MeSH term "femoro-acetabular impingement" yielded 3315 publications. We recorded 327 articles after filtering for English, humans only, no preprints, and all ages. Based on the title and abstract, 39 articles were shortlisted after a thorough review by two investigators, who finally selected 30 articles (four systematic reviews, 18 original studies, six review articles, one clinical trial, and one book chapter) for analysis. FAI appears to be primarily mechanical rather than inflammatory, with radiographic findings often not correlating with clinical severity. As the skeleton matures, the angle of the acetabulum increases, and early closing of the triradiate cartilage leads to pincer-type FAI.