Femoral Acetabular Impingement (FAI)
Femoral acetabular impingement (FAI) is a hip condition in which extra bone forms at the junction between the ball (femoral head) and the adjacent neck at the top of the thigh bone. The extra bone usually forms in adolescence from participating in activities that involve repetitive hip flexion and rotation.
It is believed that the growth plate in this area becomes overactivated by the repetitive stress, which causes a localized area of bone growth called a CAM lesion. Parts of the rim of the acetabulum may also overgrow and this is called a pincer lesion. Frequently, extra bone can grow under a bony prominence of the pelvic bone (called the anterior inferior iliac spine) and above the rim. After a CAM and/or pincer is formed, hip flexion and rotation causes the bony prominences to pinch soft tissue structures in between. The predominant structure that gets pinched is the labrum, which attaches nearly circumferentially to the rim of the socket. With repetitive pinching, the labrum can separate from its attachment to the rim and adjacent cartilage. This is called a labral tear. Patients can have isolated CAM, pincer, or combined impingement, but combined FAI is the most common.
This condition often limits people from being able to exercise and participate in activities that involve deep hip flexion and rotation such as squats or lunges. Abnormal hip joint mechanics from FAI lead to compensatory pelvic motion, which can lead to other hip/pelvic disorders including: sacroiliitis, pubic symphysitis, and trochanteric bursitis. Patients with FAI are usually first treated with physical therapy and anti-inflammatory pain medication, but since it is a mechanical problem, surgery is usually the best and most definitive option. Minimally invasive techniques (i.e. hip arthroscopy) are used to reshape the bone on both the femoral and acetabular side. With surgery, there is a high rate of return to previous activities and success with helping patients recover their function and quality of life.
- Pain localized to the groin that may radiate to the side and back of the hip
- Decreased hip range of motion, particularly with hip flexion and rotation
- Weakness from pain
- Physical Therapy - A formal course of physical therapy (PT) is the first line of treatment. A formal course of physical therapy for hip and core strengthening can help patients regain their strength and hip range of motion. PT should not be aimed at trying to improve the range of motion because the altered hip anatomy causes a mechanical block that cannot be overcome with stretching. In fact, aggressive stretching exercises can often make the pain worse.
- Injection - Diagnostic injections are frequently used to determine or confirm if pain in the hip region is coming from the joint. An ultrasound is used to guide a needle into the hip joint and a numbing medicine called lidocaine and/or marcaine is injected. If the pain is alleviated after the injection, then this confirms that the pain is coming from the joint. This also indicates that patients would respond well to surgery if this is needed.
- Surgery - Because FAI is a mechanical problem, often the best treatment is a hip arthroscopy, which is a minimally invasive technique through which the structures in the hip can be visualized and the areas of extra bone removed. The bone is reshaped to be more anatomic, which eliminates the pinching that is caused by this condition. This usually helps patients regain their hip function and quality of life allowing them to return to their desired activities.
After taking a detailed history and performing a thorough exam, x-rays will be obtained. FAI is diagnosed by identifying the areas of extra bone around the hip. Because most cases of FAI are associated with a tear of the labrum in the hip, an MRI with IV contrast is usually ordered. This allows for visualization of the labrum and cartilage in the hip.
Treatment depends on a patient’s age, activity levels, goals, and presence of a labral tear. Surgery is usually recommended because FAI is a mechanical problem that causes impingement on the labrum and can also damage the adjacent cartilage potentially causing irreversible damage that can lead to arthritis. While symptoms can improve with conservative treatment, it does not cause the areas of extra bone to go away.
The most common risks are stiffness, persistent pain, and weakness. Patients with a FAI and/or a labral tear commonly use their injured hip less, which causes the hip muscles to weaken leading to decreased function and confidence with more vigorous activities.