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FEMOROACETABULAR IMPINGEMENT (FAI) 2017-06-05T14:29:51+00:00

Anatomy

The hip is functionally a ball and socket joint. It consists of the head of the femur (the ball) and the acetabulum (the socket). Both the ball and socket are covered with articular cartilage, which allows smooth, almost frictionless gliding between the two surfaces. The edge of the acetabulum is surrounded by a fibrous structure that envelops the femoral head, the ‘labrum’. The labrum acts as a seal, or gasket, around the femoral head. However, this is not its only function, as it has been shown to contain nerve endings, and therefore may be painful if damaged. A total of 27 muscles cross the hip joint, making it a very deep part of the body for arthroscopic access. This is one reason why hip arthroscopy can be technically demanding.

Cam-type femoroacetabular impingement

Cam impingement is created by the abnormal development of the femoral head-neck junction. This type of deformity is characterised by varying amounts of abnormal bone on the anterior and superior femoral neck. A bony protrusion or bump has been likened to a cam, an eccentric part of a rotating device. This leads to joint damage as a result of the non-spherical femoral head being forced into the acetabulum, mainly with flexion and/or internal rotation. This may impart compression and shear forces to the articular cartilage, and may lead to labral tears and peeling away of the articular cartilage from the underlying bone, leading to early arthritis.  Standard arthroscopic treatment of symptomatic cam FAI involves resection or repair of any labral and chondral injuries, and subsequent reshaping of the head-neck junction of the upper femur using high-speed motorised burrs.

Pincer-type femoroacetabular impingement

In contrast, pincer impingement is a result of an abnormality on the acetabular side of the hip joint. The acetabulum may either have a more posterior orientation than normal, otherwise known as acetabular retroversion, or there may be extra bone around the rim. This results in contact of the femoral neck against the labrum and rim of the acetabulum during hip movement earlier than might otherwise be the case. Repeated contact between the femoral neck and the edge of the acetabulum may lead to damage to the labrum and adjacent articular cartilage. Bone formation, or ossification within the labrum may be commonly seen as a result of this repeated contact. It is thought that this type of impingement may also predispose to the development of osteoarthritis.  The goal of the arthroscopic treatment of pincer impingement is to reduce the acetabular over coverage of the hip. Methods to reduce this over coverage of the ball by the socket include labral detachment, acetabular rim recession using burrs, often reattaching the labrum with anchors at the end of the procedure.

Labral tears

The acetabular labrum is a fibrous structure, which surrounds the femoral head. It forms a seal to the hip joint, and is an important adjunct to the lubrication of the joint. The labrum also has a nerve supply and may cause pain if damaged. The underside of the labrum is continuous with the acetabular articular cartilage so any compressive forces that affect the labrum may also cause articular cartilage damage, particularly at the junction between the two, the chondrolabral junction. The labrum may be damaged or torn as part of an underlying process, such as FAI or dysplasia (shallow hip socket), or may be injured directly by a traumatic event. Depending on the type of tear, the labrum may be either trimmed (debrided) or repaired. Various techniques are available for labral repair, mainly using anchors, which may be used to re-stabilise the labrum against the underlying bone, allowing it to heal in position.

For more indept surgical information regarding the treatment of femaroacetabular impingement you can visit Mr Stafford’s dedicated surgical website http://gilesstafford.com