Femoral Acetabular Impingement (FAI)

Summary

In femoral acetabular Impingement (FAI), either the femur or the acetabulum of the hip joint is not shaped quite right and therefore the hip does not move as smoothly as it should. This can cause damage to various hip structures including the tissue around the edge of the hip socket (labrum) and/or the smooth articular cartilage of the hip joint. This mechanical impingement can result in pain and decreased hip range of motion.

Treatment of FAI depends on the severity of the disease. Non-operative treatment is usually recommended before pursuing surgery. Non-operative treatment includes physical therapy, pain medications such as non-steroidal anti-inflammatory drugs (NSAIDs), and activity modification to avoid activities that cause pain. If non-operative treatment is not sufficient, arthroscopic hip surgery to shave off the extra bone and smooth the articulating surfaces is recommended.

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Clinical Presentation of Femoral Acetabular Impingement

Femoral acetabular impingement results from excess bone formation on the surface of the femur and/or acetabulum, preventing smooth hip movement. There are two main types of femoral acetabular impingement, Cam and Pincer impingement. These are differentiated by which bone of the hip joint is causing the impingement. In the Cam type of FAI, the femoral head is not round enough, usually due to extra bone formation resulting in an uneven surface. The Pincer type of FAI occurs when the acetabulum has extra bone hanging over its edges, causing impingement with certain movements of the hip joint (Figure 1). A combination of Cam and Pincer impingement can also occur.

Figure 1: Pincer and CAM Types of Femoral Acetabular Impingement

The Cam type of impingement is more common in young males and the Pincer type is more common in middle-aged females. CAM and pincer morphologies are common in the general population, and many individuals with these bony shapes never develop symptoms. However, CAM deformities are seen more frequently in athletes who participated in high-impact sports during adolescence, particularly soccer, hockey, basketball, and football.

The pain associated with femoral acetabular impingement is usually located in the groin area and is typically made worse by exercise, getting in and out of a car, leaning forward, and prolonged sitting. Pain is commonly described as a dull ache but can feel sharp or stabbing when performing complex movements such as twisting or squatting. Symptoms of FAI can also be referred to the side of the hip, the buttocks region or even the knee. In addition, individuals with FAI may complain of a stiff hip with limited range of motion, with or without pain. Another symptom includes a limp while walking, favoring the unaffected side.

Repeated impingement can damage the labrum, a ring of cartilage around the hip socket. Labral tears are common in patients with FAI and may contribute to pain, clicking, catching, and feelings of instability. Some patients with FAI may develop premature osteoarthritis of the hip over time, particularly if significant cartilage damage has already occurred. However, not everyone with FAI develops arthritis.

Exam Findings in Femoral Acetabular Impingement

The diagnosis of femoroacetabular impingement requires BOTH symptoms and imaging findings. Many individuals have CAM or pincer deformities visible on X-rays but never experience hip pain. A common physical exam finding in femoral acetabular impingement is known as the C-sign. This is when the individual is asked to show where the pain is coming from and proceeds to form a “C” with their hand in order to cup it around the front of the affected hip. Another common finding, and the most sensitive physical exam maneuver for this condition, is a positive FADIR or anterior impingement test. A positive test means that pain is experienced when performing this test. FADIR is an acronym for flexion, adduction and internal rotation. As such, the doctor will bring the knee up toward the chest and rotate the hip inwards so the knee is pointing toward the opposite shoulder. In addition to pain, there will be limited range of motion seen while performing the FADIR test.

Imaging

X-rays are the initial imaging ordered when a diagnosis of femoral acetabular impingement is suspected. X-rays will reveal areas of excess bone, allowing for the identification of Cam and Pincer deformities. It should be noted that many people have radiographic evidence of FAI but never develop symptoms. X-rays may also show consequences of FAI such as osteoarthritis. An MRI may be obtained to better visualize damage that may have occurred to soft tissue structures of the hip such as the labrum and cartilage. In some cases, an MRI arthrogram, which involves injecting dye into the joint before the MRI, may provide additional detail.

Non-Operative Treatment of Femoral Acetabular Impingement

The underlying bony shape associated with FAI does not change without surgery. However, symptoms may improve considerably with activity modification, physical therapy, and other non-operative treatments. Some patients remain stable for many years without surgery. In general, various non-operative treatments are recommended before surgical intervention is considered. One common non-operative treatment is activity modification. This involves limiting, changing or avoiding activities that worsen pain. On occasion, it is challenging to effectively modify activities for various reasons. This is a major factor in deciding whether to pursue surgery or not. Pain medications such as ibuprofen and other NSAIDs can also help to control the pain. Additionally, physical therapy and a home exercise program may be recommended to strengthen the muscles around the hip joint and improve range of motion. This can lead to reduced pain and increased function in the affected hip.

Operative Treatment

Surgery for femoral acetabular impingement may be performed if non-operative treatment is unsuccessful and there is evidence of damage to the joint structures, such as a tear of the labrum. Patients with hip osteoarthritis in addition to FAI may not do well following surgery. There are two main surgical treatments that can be performed depending on the extent of the disease. These are arthroscopic hip surgery and surgical hip dislocation.

Hip Arthroscopy

Arthroscopic hip surgery has become the surgery of choice to treat femoral acetabular impingement because it is less invasive compared to open surgery. It involves the use of a small camera and other instruments inserted into the hip joint through incisions in the skin. The surgeon can repair or remove damaged articular cartilage and labrum as well as trim the excess bone off the femoral head or acetabulum.

Surgical Hip Dislocation

Surgical hip dislocation is now relative uncommon and reserved for patients who have: very large CAM lesions, complex deformities, revision surgeries, or certain pediatric hip disorders. An open surgical hip dislocation involves performing the same procedures of trimming bone and repairing or removing damaged tissue as seen in hip arthroscopy. However, it differs in that it is performed by exposing both the head of the femur and surface of the acetabulum by temporarily dislocating the hip. In patients over 60 years of age who have femoral acetabular impingement in addition to osteoarthritis, a total hip replacement may be a better surgical option.

Edited by Stephen Pinney MD, August 16th, 2026.