Femoroacetabular Impingement, also known as FAI, is a source of hip pain usually presenting in young to middle age adults not necessarily associated with an injury. It is caused by abnormal contact and joint wear between the femoral head and the acetabulum (ball and socket joint). The lining of the hip joint, like other synovial joints, is made of hyaline cartilage which is very smooth and limits wear forces in the hip joint. Femoroacetabular impingement can cause injury to the articular surface of the joint and can also lead to labral tearing.
It is most often seen in the athletic population where increased and repetitive joint forces can lead to painful impingement and labral (tissue around the hip joint) tearing. It may also be seen in the general population usually as a result of early developmental hip abnormalities such as Legg Perthes Disease or SCFE (Slipped Capital Femoral Epiphysis) as an adolescent. Individuals who perform physical labor that requires frequent deep hip flexion especially under load are also at risk.
There are two types of described femoroacetabular impingement.
The Pincer lesion in which the hip socket is abnormally deep covering a large portion of the femoral head leading to impingement of the femoral neck and labrum as the hip goes through a range of motion. Pincer lesions are seen more commonly in female athletes.
Cam impingement is the second form of femoroacetabular impingement. It is caused by an abnormal shape of the femoral head or femoral neck and sometimes described as a pistol grip deformity. In this type, the femoral neck impinges on the acetabulum and labral complex most commonly in deep hip flexion leading to labral tears and abnormal joint wear.
Both types of impingement can lead to premature osteoarthritis and maybe unilateral or bilateral.
The symptoms that may be present are usually pain with weight bearing often associated with hip flexion. Pain is most often located in the groin or lateral hip and buttock and may be associated with a painful popping or crepitus. Those affected may also describe a locking sensation in the groin region.
The diagnosis is made by an orthopedic provider after taking a good history and physical exam. X-rays and MRI arthrogram may also aide in the diagnosis. Other causes of hip pain both inside and outside the hip joint must be considered and ruled out.
Treatment will depend on the cause of the impingement but initially will be rest, possible crutches, NSAIDS, physical taherapy and avoidance of physical exercises that increase pain. Weight loss can also aid in reduction of pain. In some cases, intraarticular corticosteroid injections maybe very effective in reducing inflammation and pain.
Surgical indications are failure of conservative treatment or anatomic changes that only surgery can remedy. Surgery may be arthroscopic or an open procedure depending on each individual case.