|The hip joint is a synovial, ball (femoral head) and socket (pelvic acetabulum) joint (a diarthrosis). When abnormal contact occurs, the femoral head causes painful pinching (impingement) as it meets the acetabulum, compressing and sometimes tearing the cartilaginous ring that surrounds the acetabulum (acetabular labrum). Femoral acetabular impingement (FAI) is most likely to occur during twisting or pivoting activities or at the extreme range of motion when hip joint movement has become stiff from underlying osteoarthritis.|
There are 2 main types of FAI: cam and pincer. With cam (from the Dutch word for "cog") FAI, the ball of the femoral head is not completely rounded at the femoral head-neck junction, which causes an abnormal bulging of the femoral head within the acetabulum (Manaster). This can cause mechanical impingement and damage to the cartilage lining the acetabulum during hip movement. Cam FAI is most common in young, active male patients. With pincer FAI, impingement occurs from abnormal compression of the acetabular cartilage by the femoral head. This may result from an excessively deep socket that limits normal range of motion, an awkwardly oriented socket, or a bone spur (osteophyte) that catches during movement. Pincer FAI is most common in middle-aged women. However, the majority of individuals with FAI exhibit a mixed pattern of cam and pincer types (Ganz, "Etiology"; Shah).
Chronic FAI can result in tears of the cartilage lining the acetabulum (labral tears), complete detachment of the labrum from the acetabulum, cyst formation in the bone of the acetabulum, and early degenerative osteoarthritis of the hip joint.
Risk: FAI may result from anatomical anomalies (e.g., an acetabulum that is very deep or is set on too far back on the pelvis; a femur that is excessively externally rotated), osteophytes on the femoral head, degeneration of the hip joint from previous femoral neck fracture, or from congenital hip dysplasia, in which the hip joint is abnormally shallow and poorly aligned (Manaster). Direct hip trauma, and Legg-Calvé-Perthes disease (a form of osteonecrosis of the hip), also may predispose individuals to FAI.
Symptoms of cam FAI typically usually manifest in individuals by the third decade, particularly in those with increased participation in sports (Leunig). FAI is a significant cause of hip pain in athletes, especially in those who perform twisting motions of the hip (e.g., soccer, football, ballet, hockey). In one study, 81% of professional hockey players with hip pain who needed arthroscopic surgery were found to have FAI (Philippon). Between 2001 and 2005, over one-third of Olympic and professional athletes undergoing arthroscopy for hip pain had FAI (Philippon).
Source: Medical Disability Advisor