The ball and socket joint of the hip is comprised of two bony components: the acetabulum (socket) and the femoral head (ball). Femoroacetabular impingement (FAI) describes a condition in which the movement of the hip is restricted by abnormal bony contact between the femoral head and the acetabulum. It is one of the most common sources of pain and disability in the hip. There are two principal forms of femoroacetabular impingement: Pincer impingement, which entails over coverage of the socket, and CAM impingement, which describes a non-spherical femoral head. The most common form of FAI is combined impingement in which there are elements of both CAM and Pincer impingements present at the same time. In any case, femoroacetabular impingement leads to soft tissue damage, inflammation, labral tears, cartilage damage and osteoarthritis over time as the bones of the hip rub against one another and degrade themselves and the surrounding ligaments, tendons, and articular cartilage.

Causes

Many of the bony process abnormalities we see in femoroacetabular impingement are congenital, meaning patients are born with them, or developmental in nature, meaning patients cartilage hardens into these abnormal bony shapes during adolescence.  This develops during repetitive high stress activities which causes overgrowth of bone on the femur and less often on the acetabulum. We do not know how prevalent femoroacetabular impingement is in the general population; some people can live their entire lives with the condition and not exhibit any symptoms. People who are very active or work in professions that require great exertion will generally begin to experience symptoms of femoroacetabular impingement earlier, but exercise and heavy exertion do not cause femoroacetabular impingement. 

Symptoms

Femoroacetabular impingement becomes symptomatic after the sustained bony contact between the femoral head and acetabulum has caused sufficient soft tissue damage in the hip. This damage, be it to the labrum, the articular cartilage, or the joint capsule, can lead to significant pain, weakness, instability, and gait abnormalities. The pain generally emanates from the groin area, but it can also be present on the outside or back of the hip. For some patients, certain movements–namely those that recreate the bony contact and therefore irritate the damaged soft tissue–will cause sharp, stabbing pain in the hip. For others, the pain is just a constant dull ache. Pain generally occurs with twisting activities or activities with high flexion such as sitting in low chairs or tying shoes.

Diagnosis and Treatment

To diagnose hip impingement, your physician will perform a comprehensive physical examination with accompanying family and medical history. During the exam, they will perform an impingement test, during which they bring your knee towards your chest and rotate your leg at the knee. If this movement recreates your pain, then it is very likely you have hip impingement. During your visit, your physician will likely order additional diagnostic tests, including x-ray, which allows them to analyze the ball and socket for bony abnormalities; and magnetic resonance imaging (MRI), which creates detailed views of the soft tissue structures, allowing your physician to determine the status of these vital structures. 

There are a number of treatment options available to treat femoroacetabular impingement, including surgical intervention. Your physician will likely start you on a conservative course of treatment, including activity modification to avoid bony contact or impingement in the hip, physical therapy, and non-steroidal anti-inflammatory medications like ibuprofen (NSAIDs). There are also a number of injections available to both relieve pain and help diagnose the condition. If these conservative measures fail, the next step is surgical intervention aimed at correcting the underlying structural issues in the hip. The primary goal of hip arthroscopy for femoroacetabular impingement is to repair the torn labrum using implants called anchors, reshape the ball and socket by shaving away excess bone to correct the impingement, and address any surface cartilage damage. Surgery to correct femoroacetabular impingement should ideally happen before the onset of surface/articular cartilage damage because this damage is irreversible and can lead to inferior outcomes for the procedure.

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