Femoroacetabular impingement

History

Though the idea of femoroacetabular impingement is fairly new, doctors had noted damage in that area for over a hundred years. The condition was identified as a distinct anatomical issue and a cause of hip osteoarthritis only after a specific open surgical dislocation technique was created. Orthopedic surgeon Dr. Reinhold Ganz first described FAI in a 2003 publication linking it to osteoarthritis.

Cause

Femoroacetabular impingement involves abnormal contact between the upper thigh bone and the hip socket rim. Most patients have a misshapen femoral head or socket, a misaligned junction between these bones, or a mix of these issues. The exact cause remains unclear, but both inborn and later-developing origins have been suggested. Family studies show higher rates among siblings, hinting at a genetic link, and one study found it more common in white people.

It also appears more often in males. Still, solid proof for a genetic cause is lacking; the leading theory is that the cam type, in particular, stems from repeated hip movements like squatting in young athletes. Activities that worsen symptoms include prolonged or repetitive squatting, twisting motions such as pivoting in sports, getting in and out of cars, and sitting for long periods. A combination of a mild developmental hip abnormality and environmental factors—like repeated leg motion beyond normal range—may also contribute.

Three types exist: cam (extra bone on the upper femoral head, resembling a camshaft), pincer (extra bone on the upper socket rim), and mixed, which accounts for about 70% of cases. Notably, some people without symptoms show these same radiographic findings. Current research links the cam type to later hip osteoarthritis, but no such connection has been found for the pincer type.

Diagnosis

Diagnosis of femoroacetabular impingement begins with a clinical evaluation, but this step alone rarely confirms the condition because the pain is often inconsistent and vague. The doctor should ask about the patient's childhood and current physical activities. During the physical exam, they assess passive internal rotation of the hip while it is flexed, as the range of motion decreases in proportion to the size of a cam lesion. The FADDIR test, which involves flexing the hip to 90 degrees, adducting, and internally rotating it, is considered positive if it reproduces pain.

The FABER test, involving flexion, abduction, and external rotation, is useful when a labral pathology is also present and is positive if the position causes pain. Gait changes, such as reduced peak hip extension and internal rotation used to compensate for bony overgrowth, may also be observed. Projectional radiography, or X-ray, is typically the first imaging tool, with an anterior-posterior pelvis view, a lateral view of the affected hip, and a 45-degree Dunn view recommended.

MRI may follow, especially if X-rays show no clear evidence, providing three-dimensional reconstruction to evaluate cartilage or measure hip socket angles like the alpha-angle. MR arthrogram was once used for better soft tissue detection, but modern MRI is now considered comparable. CT is rarely used due to radiation exposure and no advantage over MRI. Dynamic simulation of hip motion with CT or MRI can help determine if, where, and how much impingement occurs.

The diagnosis often accompanies a labral tear. Conditions that can mimic FAI include piriformis syndrome, labral tear without FAI, adductor muscle strain, sciatica, athletic pubalgia, gluteus medius or minimus tendinopathy, iliopsoas tendinopathy, stress fracture, femoral head osteonecrosis, other impingements such as anterior inferior iliac spine or ischiofemoral, and a loose body within the joint.

Treatment

Treatment of FAI is divided into non-operative (conservative) and operative approaches. Conservative treatment is often prescribed for those who have not yet received therapy and includes physical therapy, avoidance of activities that produce pain, and nonsteroidal anti-inflammatory drugs. It may also include joint injections with cortisone or hyaluronic acid, particularly for those wishing to avoid surgery. Physical therapy aims to improve joint mobility, strengthen surrounding muscles, correct posture, and treat other muscle or joint deficits that may be exacerbating the condition.

A movement analysis may identify specific injury-causing movement patterns. Studies on the effectiveness of physical therapy are underway with no conclusive results to date. Operative treatment is generally recommended for those who continue to have symptoms and involves surgical correction of bony abnormalities causing impingement and correction of soft tissue lesions such as labral tears. The primary aim is to correct the fit of the femoral head and acetabulum to reduce contact and allow greater range of movement, including femoral head sculpting and/or trimming of the acetabular rim.

Surgery may be arthroscopic or open. A 2011 study suggested that arthroscopic methods have outcomes equal to or better than other methods with a lower rate of major complications when performed by experienced surgeons, so surgery is now rarely done open. Outcomes of arthroscopic surgery are being studied but have generally been positive. The risk of surgery failing or needing reoperation is about 5.5%, with a complication rate of 1.7%.

Patient-reported outcomes show pain reduction and improved daily activities approximately three to six months post-operatively, and improved sport function about six months to a year. Failure of hip arthroscopy is more likely in older patients, females, or those with long-standing symptoms.

Did You Know?

• Pain is the most common complaint and is often experienced in the groin, upper buttock, lower back, side of the hip, or posterior upper leg.
• Sports such as hockey, tennis, soccer, and equestrian are associated with a higher prevalence of femoral neck abnormalities due to forced, loaded flexion and internal rotation.