Femoroacetabular impingement.

Femoroacetabular impingement (FAI) is a common cause of early-onset osteoarthritis of the hip. It can be caused by morphologic abnormalities involving the proximal femur or acetabulum, leading to abnormal abutment of the femoral head-neck against the acetabular rim. This repetitive trauma causes mechanical wear of the labrum and articular cartilage, leading to osteoarthritis of the hip. Magnetic resonance imaging is an accurate noninvasive imaging modality that can detect acetabular labral lesions and adjacent cartilage damage, and is able to detect underlying subtle anatomic variations of the femoral head-neck junction and acetabulum associated with FAI.