Femoroacetabular impingement: defining the condition and its role in the pathophysiology of osteoarthritis.

Femoroacetabular impingement (FAI) is an increasingly recognized cause of hip pain. It is best defined as a pathologic mechanical process by which morphologic abnormalities of the acetabulum and/or femur combined with vigorous hip motion lead to repetitive collisions that damage the soft-tissue structures within the joint itself. Based on cross-sectional studies in which FAI morphology was studied before the presence of radiographic osteoarthritis (OA), and on prevalence studies in younger, asymptomatic persons, it is clear that FAI and its morphologic risk factors are common in young adult hips and predispose to the later development of OA in certain patients. Longitudinal studies also support the assertion that, in middle-aged adults, the presence of cam deformities at baseline substantially increases the risk of developing OA and the need for total hip arthroplasty. More long-term data are needed to better define the natural history of pincer deformities as well as FAI in younger cohorts.