The Natural History of Femoroacetabular Impingement

Background: Structural hip abnormalities have long been suspected of causing hip osteoarthritis. The concept of deformity of the proximal femur as a cause of osteoarthritis (OA) started with description of the tilt deformity and progressed to the pistol grip, then eventually cam-type femoroacetabular impingement (FAI). Acetabular over-coverage or retroversion as a cause of impingement is commonly referred to as pincer-type FAI. The primary research question we asked was: what is the natural history of hips with FAI? Methods: We reviewed the literature to identify studies with cross-sectional and longitudinal evidence of the effect of FAI on the development of or association with hip OA. Results: In cross-sectional and longitudinal natural history studies of hip OA, cam-type FAI has consistently shown an association with developing OA. In regard to pincer-type FAI, the data are less convincing with some studies suggesting an increased risk and others showing a protective effect of the acetabular over-coverage. It is clear that not all patients with cam FAI get OA but the altered anatomy does increase the relative risk of developing OA. Conclusions: Cam-type FAI is associated with the development of hip OA; however, there is no role for prophylactic surgery in the asymptomatic hip with the anatomy predisposing to FAI. Further interventional studies are needed to determine whether surgical correction of cam-type FAI in the symptomatic hip alters the natural history of the condition.