Femoral Acetabular Impingement

FAI is a condition that can lead to hip pain, snapping and, occasionally, early degenerative arthritis of the hip. FAI occurs mostly in men between the ages of 40 -60, but women can also be affected. FAI is an anatomic condition that occurs because the hip bones are not shaped properly. The abnormal shape leads to impact between the edge of the ball and the rim of the socket with activity. This can result in damage to the surface of the hip (articular cartilage) or the supporting soft tissue structures of the hip socket (labrum).

There are two types of FAI. Cam impingement occurs when the hip ball is tilted backward causing the neck of the hip ball to “impinge” or hit up against the socket (acetabulum). This abnormality may cause damage to the hip and result in pain as well as early wear of the hip socket. The other type is pincer impingement, which occurs when the socket of the hip (acetabulum) is excessively deep or overhangs in some areas. The overhanging rim can impinge on the neck of the femur and the labrum is caught in between. In both cases, pain and arthritis can result. It is possible, and in fact common, to have both cam and pincer type hip FAI.

Symptoms typically begin with vague hip pain. Advanced symptoms include, stiffness, loss of motion and pain with activity, such as walking or climbing stairs. Occasionally, patients report a feeling of “catching” or “clicking” in the hip. The typical patient presents without any history of previous hip problems.

The diagnosis is usually made with x-rays. Specialized views are frequently necessary and may be best ordered by an orthopaedic surgeon or sports medicine specialist. There are several special findings such as an “alpha angle” and a “cross over sign” that the orthopaedic surgeon uses to distinguish cam from pincer hips. MRI may also be used to diagnose FAI. Occasionally, the MRI study is performed with contrast to evaluate for small tears that may be missed on a non-contrast MRI. In a contrast MRI, the radiologist will inject gadolinium directly into the hip joint prior to the MRI. Occasionally, a “high field machine” such as a 3T MRI, which is a strong magnet MRI, is used. CT scans with “reconstruction” are very useful as they provide a very detailed, 3D image of the bony anatomy of the hip.

Treatment for most patients begins with physical therapy and anti-inflammatory medications. While these treatments will not correct abnormal anatomy contributing to symptoms, the inflammation may be permanently reduced. A cortisone injection into the hip may also be of value. If conservative treatments do not work the patient may elect to undergo arthroscopic surgery or a “mini-open decompression”. The objective of these surgeries whether done through arthroscopic techniques or by open techniques is to reduce the impingement by reshaping the edge of the ball and/or rim of the socket. This approach is most useful in the cam type hip. The pincer hip will sometimes require a more involved surgery whereby the surgeon rearranges the position of the hip socket bone (acetabulum). This type of surgery is known as an osteotomy.

Whether FAI is treated by surgery or by non-operative means the primary goal is the relief of the symptoms. It remains unknown if correcting the anatomic abnormality of FAI will prevent the occurrence of arthritis in the future. Fortunately, the association between FAI and the development of osteoarthritis of the hip is not direct. There are many individuals walking around with this abnormality who never develop pain or findings of arthritis.