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Femoroacetabular impingement (FAI) occurs in the hip joint. Impingement refers to some portion of the soft tissue around the hip socket getting pinched or compressed. Femoroacetabular tells us the impingement is occurring where the femur (thigh bone) meets the acetabulum (hip socket). There are two different types of impingement. They differ slightly depending on what gets pinched and where the impingement occurs.
This guide will help you understand:
what parts of the hip are involved
how the problem develops
how health care professionals diagnose the condition
what treatment options are available
what Actify Physiotherapy’s approach to rehabilitation is
Anatomy
What part of the body is affected?
It's even referred to as a pistol grip deformity. The femoral head isn't round enough on one side (and it's too round on the other side) to move properly inside the socket. The result is a shearing force on the labrum and the articular cartilage, which is located next to the labrum. The labrum is a dense ring of fibrocartilage firmly attached around the acetabulum (socket). It provides depth and stability to the hip socket. The articular cartilage is the protective covering over the hip joint surface.
Sometimes cam-type impingement occurs as a result of some other hip problem (e.g. Legg-Calve-Perthes disease, slipped capital femoral epiphysis,) but most of the time, it occurs by itself and is the main problem. Men are affected by cam-type impingement more often than women.
The second type of impingement is called pincer-type impingement (more common in women). In this type, the socket covers too much of the femoral head. As the hip moves, the labrum comes in contact with the femoral neck just below the femoral head. Pincer-type impingement is usually caused by some other problem. It could be as a result of 1) hip dysplasia, 2) a complication after osteotomy surgery (cutting away bone) to correct hip dysplasia, or 3) an abnormal position of the acetabulum called retroversion. Hip dysplasia is a deformity of the hip (either of the femoral head or the acetabulum, or both) that can lead to hip dislocation.
Causes
What causes this problem?
The cause of the problem has been under considerable debate for a long time. Now with better imaging studies, we know that some subtle changes in the shape of the femoral head may be the cause of FAI. Other anatomical changes in the angle of the hip may also contribute to this problem. The basic problem is that the head of the femur butts up against the cartilage rim around the acetabulum and pinches it. An alternate type of femoral acetabular impingement causes abnormal jamming of the head-neck junction.
Normally, the femoral head moves smoothly inside the hip socket. The socket is just the right size to hold the head in place. If the acetabulum is too shallow or too small, the hip can dislocate. In the case of FAI, the socket may be too deep. The rim of the cartilage hangs too far over the head. When the femur flexes (bends) and internally rotates, the cartilage gets pinched. Over time, this pinching or impingement of the labrum can cause fraying and tearing of the edges and/or osteoarthritic changes at the impingement site. At the same time, with changes in the shape and structure of the hip, there are changes in normal hip movement. There may be too much hip adduction and internal rotation. Hip adduction refers to movement of the leg toward the body. Muscle weakness of the hip abductor muscles, hip extensors, and hip external rotators add to the problem. Hip abduction is moving the leg away from the body. With the combined effects of anatomic changes in the hip and the resultant muscle imbalances, repetitive motions can create mini-traumas to the hip joint. The result can be an additional problem: partial or complete labral tears. A complete rupture is referred to as an avulsion which indicates that the labrum is separated from the acetabular cartilage where it normally attaches.
On the next blog posting we will be discussing the symptoms of femoroacetabular impingement, but if you have any questions feel free to contact us.