Femoro-acetabular impingement (FAI) occurs when the ball (head of the femur) does not have its full range of motion within the socket (acetabulum of the pelvis). This causes a decreased range of hip joint motion, in addition to pain. Most commonly, FAI is a result of excess bone that has formed around the head and/or neck of the femur, otherwise known as “cam”-type impingement. FAI also commonly results from an overgrowth of the acetabular (socket) rim, otherwise known as “pincer”-type impingement, or when the socket is angled in such a way that abnormal impact occurs between the femur and the rim of the acetabulum.
When the extra bone on the femoral head and/or neck hits the rim of the acetabulum, the cartilage and labrum that line the acetabulum can be damaged. The extra bone can appear on x-rays as a seemingly very small “bump.” However, when the bump repeatedly rubs against the cartilage and labrum (which serve to cushion the impact between the ball and socket), the cartilage and labrum can fray or tear, resulting in pain. As more cartilage and labrum is lost, the bone of the femur will impact with the bone of the pelvis. This “bone on bone” motion is most commonly known as arthritis.
Athletes with femoroacetabular impingement usually complain of anterior groin pain that worsens with hip flexion, internal rotation, and adduction. Good results have been reported in the literature for patients treated arthroscopically for labral tears and associated femoroacetabular impingement, with as high as 93 percent of patients able to return to sports and 78 percent able to remain active at 1.5 years after surgery. For more information, see Hip Mobility and Hip Arthroscopy: A Patient's Guide to Correcting Femoro-acetabular Impingement.
Types of Hip Impingement