Femoro-acetabular impingement (FAI)

The word “femoro” comes from femur or thigh bone.  The word “acetabulum” comes from the socket in the pelvis.  The syndrome arises when the upper end of the thigh bone (the femur) impinges or bangs against the edge of the acetabulum or socket.  One single impingement phenomenon is insufficient to cause serious disease.  Unfortunately, the impingement phenomenon is repetitive and protracted.  It may occur hundreds of thousands or even millions of times over a period of years.  It is the repetitive banging or impingement that causes damage both to the socket and the edge of the thigh bone.  This is a well-accepted and, unfortunately, all too common cause of osteoarthritis of the hip joint. 

The symptoms are usually in the form of pain in the groin and occur with full hip joint flexion (bending the thigh up towards the torso) and with internal rotation (turning the affected knee in towards the other knee).  Bike riders, hurdlers, rowers and football players often note these symptoms earlier than others not so active.  The symptoms will sometimes begin in the patient’s early 20s.  As the years pass, so do the symptoms become more noticeable and frequent and, similarly, there are noted restrictions in range of motion of the joint.  Typically, the patient loses the ability to fully flex and internally rotate the hip.

The orthopaedic surgeon is able to make the diagnosis often on the basis of the history and on the clinical features noted at the time of examination.  X-rays are also very useful.  We see what we call a “bump” appearing at the junction between the upper end of the thigh bone (the ball) and the neck to which the ball is attached.  Ask your orthopaedic surgeon to point this feature out if you do suffer with FAI.  MRI scans are also very useful.  Not only can the impingement site be localised, but damage to the other structures within and around the joint can also be identified.  Typically, the socket or the acetabulum has a soft flange-like structure surrounding it called the labrum.  This labrum can become detached.  It can give rise to pain, clicking, clunking and locking.  In addition, the very specialised cartilage, or white smooth glistening material that lines the socket, can become damaged.  Mechanical attrition can result in the cartilage peeling away.  A chemical inflammatory process can also be incited.  The cartilage cells (chondrocytes) do not normally have a blood supply.  They get their nutrition by fluid being squeezed in and out with joint movement.  When the cartilage cells are exposed to the host immune system, and autoimmune reaction can be created.  This is how the arthritis from FAI can become quite rapid and severe. 

As with all things orthopaedic, the management can be either non-operative or operative.  Non-operative measures are simply directed to curtailing the symptoms.  This will include weight loss, avoiding the provocative activities and ingesting analgesics or anti-inflammatory agents. 

From an operative perspective, if it is caught early enough, the FAI symptoms can be dramatically reduced by arthroscopic or telescopic surgery.  The bump can be removed from the femoral neck, the labrum can be re-attached to the edge of the socket, and any spurs that have formed can also be removed. 

While this type of arthroscopic surgery may theoretically retard or even prevent the subsequent appearance of osteoarthritis of the hip joint, the research so far is inconclusive.  It is to be hoped that longitudinal studies that are currently being performed will provide some evidence (one way or the other) over the next few years. This is a space to be watched.