Femoroacetabular impingement (FAI) is a condition where there is too much friction in the hip joint from bony irregularities causing pain and decreased range of hip motion. The femoral head and acetabulum rub against each other creating damage and pain to the hip joint. The damage can occur to the articular cartilage (the smooth white surface of the ball or socket) or the labral tissue (the lining of the edge of the socket) during normal movement of the hip. The articular cartilage or labral tissue can fray or tear after repeated friction. Over time, more cartilage and labrum is lost until eventually the femur bone and acetabulum bone impact on one other. Bone on bone friction is commonly referred to as Osteoarthritis.
FAI impingement generally occurs as two forms: Cam and Pincer.
CAM Impingement: The Cam form of impingement is when the femoral head and neck are not perfectly round, most commonly due to excess bone that has formed. This lack of roundness and excess bone causes abnormal contact between the surfaces.
PINCER Impingement: The Pincer form of impingement is when the socket or acetabulum rim has overgrown and is too deep. It covers too much of the femoral head resulting in the labral cartilage being pinched. The Pincer form of impingement may also be caused when the hip socket is abnormally angled backwards causing abnormal impact between the femoral head and the rim of the acetabulum.
Most diagnoses of FAI include a combination of the Cam and Pincer forms.
Symptoms of FAI
Symptoms of femoroacetabular impingement can include the following:
- Groin pain associated with hip activity
- Complaints of pain in the front, side or back of the hip
- Pain may be described as a dull ache or sharp pain
- Patients may complain of a locking, clicking, or catching sensation in the hip
- Pain often occurs to the inner hip or groin area after prolonged sitting or walking
- Difficulty walking uphill
- Restricted hip movement
- Low back pain
- Pain in the buttocks or outer thigh area