Femoral-Acetabular Impingement (FAI)
The hip joint is a ball and socket joint that is formed from the femur, or thigh bone, and the acetabulum, or the hip socket. In an ideal hip, these parts fit together perfectly like a puzzle. Both the ball and socket are lined in a smooth cartilage that cushions the joint, called articular cartilage. On the rim of the socket, there is a specialized fibrocartilage called the labrum. The labrum helps to suction seal the joint and acts as a gasket to keep the joint fluid in the joint.
In many hips, the head of the femur (ball) and the acetabulum (socket) don’t fit together perfectly, causing abnormal contact and friction in the joint. This underlying structural problem of the hip is called hip impingement, or femoroacetabular impingement (FAI). After repetitive contact from repetitive activities, like running or kicking, FAI causes the joint to get inflamed and become painful. If left untreated, it can also cause cartilage damage and progress the development of arthritis in the hip joint.
Femoral-Acetabular Impingement (FAI)
Causes & Triggers
FAI is caused by abnormal bone development. It happens when your bones don’t grow properly in childhood. One or more abnormal bone growths form. This creates an unevenness that restricts movement. The ball and socket rub or press against each other instead of gliding smoothly and easily.
- Genetics/heredity (abnormal development)
- High-level athletics
There are three forms of FAI: CAM impingement, Pincer impingement and Mixed impingement (involving both CAM and pincer type). In CAM impingement, the femur (ball) has boney growth on it that contacts the hip socket during movement. In pincer impingement, the acetabulum, or socket, covers the ball too much causing abnormal contact. The accompanying videos show the anatomy of each type of impingement.
Signs & Symptoms
Symptoms include pain and stiffness in your hip. You may feel a deep ache, or your pain may be sharp. You may develop a limp.
- Dull ache
- Pain (especially groin, outer thigh)
- Sharp, stabbing pain when turning, twisting, squatting
Tips & Treatment
Conservative treatment of FAI includes a course of anti-inflammatory medications, a dedicated home exercise program to strengthen the hip, and modifying activities to avoid aggravating the impingement. Activities including deep squats, lunges, and walking/running on a treadmill should be avoided. The upright stationary bicycle, elliptical trainer, and swimming are usually well tolerated. A standing desk can decrease symptoms if one’s work requires prolonged sitting. Cortisone injections play a limited role in the treatment of FAI, since they provide only short‑term relief. Patients can expect to see changes in symptoms within 6 weeks of implementing the above modalities.
If these conservative treatments do not relieve pain, the condition is treated with an outpatient arthroscopic surgery to reshape the hip joint and prevent the impingement of the femoral head on the acetabular rim. Prior to the surgery, a low radiation CT scan is obtained to help plan the surgery. A 3D image is created from the scan and the rotational alignment of the socket and the thigh bone is calculated. This information helps guide the surgical plan. The outpatient surgery is done arthroscopically to minimize damage to the hip joint and muscles surrounding the hip. A burr is used reshape the ball and socket so they better match, and the labrum is reattached to the edge of the socket using bone anchors. This reshaping and/or repair work restores the proper anatomy of the hip, giving the patient the greatest chance of avoiding recurrence of symptoms – and may delay the onset of early arthritis or other related future hip problems.
After surgery, patients are on crutches for a minimum of four weeks. They are able to place weight on the foot and should walk in a heel-to-toe fashion. Patients will attend physical therapy for three to five months depending on their goals and progression. Patients with desk jobs return to work at 4–6 weeks, those with moderate physical jobs (e.g. nursing) return at 12 weeks, and those with highly physical jobs return to full duty in four to five months. Individuals who have the flexibility to work initially from home can return to work much sooner. The majority of the recovery occurs in the first six months and return to sport typically occurs at six months.