I am sure that most of you would have seen this term used in radiology reports for hip x-rays. As the name suggests, FAI or Femoro Acetabular Impingement is where the edge of the acetabulum (socket) or the cup impinges against the neck of the femur, usually at the end of range of motion, or the extreme of range of motion. It can be pincer type, which is often due to the socket being too deep, or the cam type, where the femoral head and neck offset is lost. The impingement often incurs in a position of flexion, adduction, and internal rotation. It often presents in middle age with subtle symptoms including groin pain (Figure 1), particularly with activities that involve rotation of the hip (e.g. playing golf) or with prolonged sitting.
Repetitive impingement leads to labral damage and then damage to the articular cartilage. The articular cartilage peels away from the underlying bone. These changes usually start at the antrosuperior aspect of the acetabulum. This progresses to early onset of arthritis
Diagnosis is usually made with the high level of suspicion from above symptoms, reproduction of symptoms with flexion, adduction, and internal rotation of the hip (position of impingement). It is usually confirmed with plain x-rays of the hip (Figure 3). A CT scan and MRI are usually done to further assess the underlying cause of impingement, as well as to assess secondary damage (e.g. labral damage and articular cartilage damage). FAI can be treated arthroscopically, where excess bone from the head and neck junction of the femur and/or from the edge of the acetabulum can be removed. This stops any further impingement and therefore any further damage to the labrum and the articular cartilage. The labral and articular cartilage can also be treated arthroscopically. This is provided that the secondary arthritic changes are not advanced. Once the arthritis becomes advanced, then often the only treatment is hip replacement, which can be severely limiting in these young patients. Therefore it is important to diagnose and treat this condition in a timely manner. Would be happy to do a more detailed presentation, if you would like more information.