Hip impingement, or FAI, occurs when the hip joint experiences excessive friction or rubbing, causing pain and difficulty moving. It can be classified as cam or pincer impingement and can be congenital or develop over time. Diagnosis involves a physical exam and X-ray, and treatment may involve surgery or hip replacement.
Hip impingement, also called femoroacetabular impingement, or FAI, occurs when movement of the hip joint causes excessive friction or rubbing. This often causes groin pain and difficulty moving the joint, and can sometimes lead to arthritis. These symptoms are often not apparent during the early stages of the condition, so FAI often goes undiagnosed for years. When it appears, it can be classified into one of two forms: cam and tong. Conflict can be congenital, or present at birth, or develop over time, and is often due to a combination of genetic predisposition and environment.
The hip joint, formally called the acetabulofemoral joint, is a ball and socket joint between the femur and the acetabulum. The femur is the large bone that extends from the knee to the hip, and the acetabulum is an inward-curving portion of the pelvis. The ball end of the femur fits into the socket-shaped shape of the acetabulum, allowing the leg to perform rotational movements. In a healthy joint, the bones glide painlessly with the help of lubricating synovial fluid and the cartilage that acts as a cushion between the femur and pelvis. If one of the bones is deformed, however, it can cause friction, cartilage destruction, and pain.
A cam hip impingement occurs when the head of the femur is not shaped properly, usually due to an injury to the bone. This can cause discomfort during forward motion, such as when pulling the knee to the chest or riding a bicycle. This condition causes abnormal force on the acetabulum and wear and tear of the acetabular cartilage. A cam hip impingement can occur for congenital or developmental reasons. Trauma can cause a deformity in the bone, or a patient can suffer from coxa vara, slipped capital femoral epiphysis (SCFE), or avascular necrosis (AVN).
AVN occurs when blood vessels that serve bone are damaged, causing it to deteriorate. Injuries, chronic steroid use, and alcoholism can contribute to this condition. Coxa vara occurs when the angle between the ball of the femur and the shaft of the bone becomes too narrow, causing the leg to shorten and uneven weight distribution. Normally, the ball is on the end of a neck that projects at an angle greater than 120 degrees from the end of the femur. SCFE affects children when the ball of the femur slips off the neck of the bone, causing severe pain and stiffness.
A pincer impingement of the hip occurs in patients whose acetabular rim grows over the head or ball of the femur. This creates a contact point between the acetabulum and the ball of the femur, which impedes movement and causes a pinching of the cartilage. Pincer FAIs are frequently found in patients who have a particularly deep or irregularly angulated hip socket. Often, a patient will have both a hip impingement and a pincer.
A doctor can use a combination of methods to diagnose FAI. The doctor will review the patient’s history, listen to symptoms, perform a physical exam, and usually take an X-ray. An MRI scan (MRI scan) may also be ordered to rule out other causes of stiffness and pain. If the patient is diagnosed with hip impingement, the doctor may try to surgically correct the shape and orientation of the joint. If the cartilage damage is severe, however, a hip replacement may be the best option.
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