Femoroacetabular impingement (FAI), also known as hip impingement, is a common cause of hip and groin pain, especially among people between the ages of 20 and 45.

It occurs when the bones of the hip joint are not shaped properly, causing them to rub against one another. This can damage the labrum—a ring of tissue that serves as a shock absorber in the hip—as well as the cartilage in the hip joint. If it isn’t treated, FAI can result in osteoarthritis.

The good news is that several treatments are available for FAI, from activity modification to physical therapy to surgery.

“Treatment of FAI has advanced significantly in recent years,” says Yale Medicine orthopaedic surgeon Andrew Jimenez, MD. “If surgery is necessary, FAI can often be adequately treated arthroscopically rather than through an open approach. This allows patients to have outpatient surgery and get back to the things they like to do faster.”

To understand FAI, it is useful to start with the basics of how a normal hip joint works. A joint is the place where two or more bones come together. In the hip, the head of the femur—the thigh bone—meets the acetabulum, which is part of the pelvis.

The hip is a “ball and socket” joint. The “ball” is the rounded head of the femur, which fits inside the “socket,” the bowl-shaped acetabulum. A thin, tough layer of articular cartilage covers the femur head and acetabulum, protecting them and helping them glide smoothly over one another when the joint flexes as you walk.

FAI a condition in which one or both bones of the hip joint are irregularly shaped, causing them to rub against one another. The friction between these bones can cause tears in the labrum and damage the articular cartilage, which may increase the risk for osteoarthritis.

There are three types of FAI:

• Cam lesion, in which the head of the femur is not shaped properly. Instead of being ball-shaped, there is a bony bump on the femur head that prevents it from fitting properly into the acetabulum. When the hip flexes, the abnormally shaped head rubs against the acetabulum, damaging the articular cartilage and labrum.
• Pincer lesion, which occurs when extra bone grows at the rim of the acetabulum. The femoral head rubs against the excess bone when the hip flexes, damaging the labrum, as well as the articular cartilage on the head of the femur.
• Combined or mixed lesion, in which both the head of the femur and rim of the acetabulum are abnormally shaped due to the growth of excess bone.

Researchers don’t yet know what causes the excess bone growth associated with FAI. Some studies suggest that genetic factors may play a role. Others suggest that participation in intense sporting activities during adolescence—when the bones are still developing—may also be a factor. Other hip disorders such as Perthes disease and slipped capital femoral epiphysis have also been linked to FAI.

The main symptom of FAI is pain, usually in the groin or hip, but sometimes in the buttock, lower back, thigh, or knee. The pain may occur during or after intense physical activity/sports such as soccer, basketball, or dance, among others. It can also develop while sitting with the hips flexed at a 90-degree angle for prolonged periods of time. People with FAI may also experience stiffness or a “popping,” “clicking,” or “catching” sensation in the affected hip.

Pain caused by FAI is often initially mild and may remain so for years. But symptoms can worsen rapidly, causing debilitating pain that stops people from participating in sports or other physical activities. 

To diagnose FAI, your doctor will review your medical history, conduct a physical exam, and order diagnostic imaging tests. Sometimes an injection may be necessary to confirm the diagnosis.

To begin, your doctor will ask about symptoms and whether you’ve had a past hip injury or disorder. He or she may ask if you participated in sports as an adolescent and whether and how frequently you currently play sports or engage in other intense physical activities.

During the physical exam, your doctor will closely examine the affected hip—bending, rotating, and flexing it to evaluate range of motion and determine which positions or movements cause pain.

Diagnostic imaging tests are necessary to confirm FAI. These may include X-rays, magnetic resonance imaging (MRI) scans, and computed tomography (CT) scans of the hip.

There are two broad forms of treatment for FAI: nonsurgical and surgical.

Nonsurgical treatment. Usually, the initial treatment of FAI is nonsurgical. These treatments include:

• Activity modification. This involves reducing or avoiding activities that cause or aggravate symptoms.
• Nonsteroidal anti-inflammatory medications (NSAIDs). Drugs such as ibuprofen and naproxen reduce inflammation and can help alleviate symptoms.
• Steroid injections. Steroid injections in the affected hip can reduce inflammation and lessen symptoms.
• Physical therapy. Stretches and exercises can help reduce symptoms, strengthen hip muscles, and improve range of motion.

Surgical treatment. Doctors may recommend surgical treatment to patients whose symptoms do not improve with nonsurgical therapies. The aims of surgery are to remove or shave down the part of bone that causes the impingement and treat damage to the labrum and articular cartilage. In many cases, surgery for FAI can be done using minimally invasive arthroscopy. In other cases, open surgery is the best option. Open surgery typically involves a longer recovery period than arthroscopic procedures. After undergoing surgery, patients usually need physical therapy to rebuild strength and improve range of motion.

Treatment can effectively reduce symptoms and many patients, including those who undergo surgical procedures, are able to make a successful return to sporting and other everyday activities. People with untreated FAI, however, may be at increased risk for arthritis in their affected hip due to damage to the articular cartilage of the head of the femur and/or acetabulum.

“At Yale medicine, we take a patient-specific approach to every patient,” says Dr. Jimenez. “No two hips are exactly alike. As a result, we get three-dimensional imaging of every patient and use intraoperative computer guidance to ensure we achieve the best treatment and optimize outcomes for our patients.“