Also known as FAI, this condition occurs when an abnormality in the shape of the ball or socket leads to boney impingement or restricted movement that causes damage to the labrum and cartilage surfaces of the joint. The labrum is a ring of soft tissue that surrounds the edge of the hip socket and provides stability to the joint.  Repeated impingement may cause progressive damage to the labrum resulting in a labral tear or labral degeneration.

FAI usually becomes symptomatic in young and middle-aged adults and may be precipitated by engaging in repetitive activities that places the hip greater than normal range of motion. Symptoms include groin and thigh pain which may be positional, giving away of the hip or instability and mechanical symptoms such as locking, grinding or clicking.

Two anatomical variants of FAI have been described and include the Cam and Pincer deformities. The Cam deformity describes a convex prominence of bone at the junction of the femoral head and neck on the upper and anterior aspect. This is the more common variety and is felt to more common in males. The Pincer deformity describes a spur of bone projecting from the upper edge of the hip socket and is felt to be more common in females. Some patients will have a combination of both deformities. Typically activities that involve high flexion of the hip along with internal rotation may cause bone impingement in the presence of these deformities alone or in combination.

The diagnosis of FAI is based on a careful history, physical examination and imaging studies. Physical exam findings may include limited range of motion, pain at the extremes of flexion and internal rotation, and sometimes the elicitation of an audible and painful clunk with circular rotation of the hip. The exam can also be helpful to eliminate other diagnoses such as hip bursitis and hip flexor tendinitis.

Initial imaging studies include x-rays which may show a Cam and/or Pincer lesion and indicate any co-existing early arthritis. Special views such as the Dunn view have been described to better highlight bone deformities. The diagnosis and severity can be confirmed by CT scanning. This allows 3D modeling of the bones which can provided a better quantitative measure of the abnormality and also aid in any surgical planning for bone removal. MRI scans with dye injected into the joint can also be helpful when looking for associated labral tears which do not appear on regular x-rays or MRI scans.

Treatment of FAI generally with starts with a conservative approach that seeks to restore normal range of motion to the stiff joint. Strengthening of the core and hip abductor muscles can help improve hip stability. Therapy can use other modalities such as ultrasound, muscle stimulation and taping to reduce inflammation and unload stress from the affected areas. Injection therapy with cortisone can provide pain relief in cases of severe pain. While cortisone does not cure the disorder it may sufficiency reduce the pain to help patients get more benefit from the physical therapy. Reducing inflammation in the joint may promote improved flexibility.

When conservative treatment fails to restore sufficient comfort and function, surgical intervention becomes an option. The goal of surgery is to remove the abnormal impinging bone and create more space to promote range of motion without impingement. This can generally be done either arthroscopically or through a limited muscle sparing open approach. Arthroscopy allows complete visualization of the joint to assess any other damage that needs to be addressed such as labral tears or loose bodies. These can be treated at the same time if necessary. Arthroscopy also allows the surgeon to grade the severity of the arthritis.

Recovery from surgery depends to some degree on whether or not patients require a labral repair at the same time. If treatment is limited to removal of impinging bone and degenerated labral tissues, patients can generally progress activities as tolerated. Physical therapy to maintain range of motion and improve core strength postoperatively is beneficial.