The Biomechanics of Femoroacetabular Impingement

Femoroacetabular impingement (FAI) is proposed as a possible biomechanical etiology of early, idiopathic hip osteoarthritis (OA). Two primary mechanisms are proposed: cam impingement and pincer impingement. In cam impingement, an abnormally shaped or excessively large femoral head or neck abuts against the anterosuperior acetabulum. In pincer impingement, overcoverage of the proximal femur by the acetabulum results in impingement. In severe cases, a contre-coup mechanism results in an anterosuperior contact point that functions as a fulcrum and produces posteroinferior impingement as the femoral head is levered out of the acetabulum. However, these proposed mechanisms are made on the basis of surgical observation rather than in vivo documentation of FAI, and controversy exists as to whether surgical interventions should be made on the basis of these theories alone. In this review of FAI biomechanics we discuss the proposed biomechanical mechanisms of FAI, the analytical methods currently available to study FAI biomechanics, and the topics that future biomechanical studies of FAI will need to address. Ultimately, a better understanding the biomechanics of FAI may help physicians design interventions that decrease the risk of progression to hip OA.