Femoroacetabular Impingement (FAI) in the Hip


An HSS study revealed that injuries to the hip joint represent nearly 10% of all injuries in the NFL. Although most of these injuries are muscle strains around the hip, other causes include damage inside the hip joint. One such injury is femoroacetabular impingement (FAI). Femoroacetabular impingement is not just found in professional athletes; many recreational athletes are also affected.

Hip Anatomy

Illustration of the anatomy of the hip
Anatomy of the hip (Illustration courtesy of the Journal of Musculoskeletal Medicine)

The hip joint is a ball-and-socket joint. The femoral head (ball) fits into the acetabulum (socket), and is held in place by the architecture of the bones and strong ligaments that surround the joint.

Around the edge of the socket, a soft cartilaginous ring called the labrum provides additional stability. The joint is also lined by a capsule and synovium, which provides lubrication. Both the ball and socket are covered with a layer of smooth cartilage that acts to cushion the joint.

Defining Femoroacetabular Impingement (FAI)

FAI is a condition where the femoral head, acetabulum or both do not fit together normally because of an incorrect curvature in one or both of these body parts. The result is increased friction during hip movements that may damage the hip joint.

When a ridge or spur of extra bone on the femoral head and/or rim of the acetabulum comes into contact during hip motion, the cartilage and labrum that line the joint can be damaged. FAI that occurs on the femoral head is known as “cam impingement,” and acetabular rim involvement is known as “pincer impingement.” Many patients often have a combination of both types of impingement.


Patients who present with symptoms of FAI often complain of pain in the groin after prolonged sitting or walking. Many athletes often describe pain in the groin with deep flexion or rotation of the hip during activity. The pain can be described as a dull ache or a sharp sensation. Occasionally, a popping or clicking in the front of the hip is described. Pain can also be felt along the side of the thigh and in the buttocks. It is important to rule out other causes of hip pain such as the low back or abdomen.

Radiographs of the pelvis are used to confirm the diagnosis of FAI. Often an MRI or CT scan is performed to further assess the cartilage, labrum, and shape of the bones.


Treatment of FAI begins with conservative, non-surgical methods. Rest, activity modifications, careful use of anti-inflammatory medications, and a course of physical therapy are often successful in alleviating symptoms. An injection of the hip joint with anesthetic can also provide some relief as well as diagnostic information in patients with symptoms which are unresponsive to treatment.

When surgery is necessary, FAI can usually be treated with hip arthroscopy to remove the abnormal bone and stabilize the cartilage and/or labrum. The procedure is performed using several small incisions through which an arthroscope, or miniature camera, and instruments are inserted into the joint. The procedure is typically performed in an outpatient setting using regional anesthesia.

Most patients resume normal activities after FAI surgery in six weeks, but full recovery may take up to six months. Studies show that 80 to 90% of patients return to athletic activity after surgery.


Femoroacetabular impingement is a common injury in athletic patients. When conservative treatment fails, hip arthroscopy is a safe and effective procedure when performed by experienced surgeons.


James E. Voos, MD
2009 Sports Medicine Fellow, Hospital for Special Surgery


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