Femoroacetabular impingement (FAI) is a condition where the bones of the hip joint come too close, causing them to collide, resulting in pain, cartilage damage, and limited mobility. Femoroacetabular impingement (FAI) occurs when the femoral head (the ball of the hip joint) and femoral neck come into contact with the acetabulum (the socket of the hip), causing friction and damage. This friction can cause injury to the labrum, a type of fibrous cartilage that acts as a cushion and stabilizer around the hip socket, and the articular cartilage, which covers the bony surfaces of the joint and provides a smooth surface for the joint to move. Over time, this damage can lead to pain, limited mobility, and a higher risk of arthritis.
FAI symptoms can range from mild to more noticeable discomfort, and in some cases, there may be no symptoms at all. The most common symptom is pain or aching in the groin or inner hip area, especially after activities like walking or prolonged sitting. Individuals with femoroacetabular impingement may also experience a locking, clicking, or catching sensation within the joint. In addition to hip pain, other symptoms include difficulty performing everyday tasks like putting on socks or shoes, trouble walking uphill, and low back pain. The pain can sometimes radiate to the lower back, sacroiliac joint (SI joint), buttocks, or the greater trochanter on the side of the hip. Since these symptoms overlap with other conditions, FAI is often misdiagnosed as hip flexor tendinitis, issues with the spine or discs, testicular pain, or sports hernia.
FAI generally occurs in two forms: Cam and Pincer. The Cam form occurs when the femoral head is aspherical, not perfectly round, leading to abnormal contact between the head and the socket during movement. The Pincer form occurs when there is excessive coverage of the femoral head by the acetabulum, usually at the front-top rim of the socket. This over-coverage results in the labral cartilage being pinched between the socket’s rim and the femoral head, causing pain and damage. Pincer impingement is commonly associated with retroversion, where the acetabulum is angled backward, or it may be due to a socket that is too deep. Both forms of impingement can occur simultaneously.
The root cause of FAI is a bony abnormality in the hip joint that cannot be corrected with physical therapy or rest. FAI can also occur when there are bone spurs on the femoral head and/or acetabulum, either due to bone overgrowth or present at birth. In particular, the femoral head may develop extra bone around its neck, or the acetabulum may grow too much bone along its rim. While the labrum or articular cartilage have limited ability to heal, not all injuries cause pain. For those with persistent symptoms, the initial treatment may involve rest and rehabilitation, but if symptoms persist, arthroscopic surgery might be necessary.