Femoroacetabular Impingement (FAI) Syndrome

What is femoroacetabular impingement (FAI) syndrome?

Femoroacetabular impingement (FAI) syndrome is a motion-related disorder of the hip comprised of symptoms (typically pain), clinical signs, and imaging findings that demonstrate premature contact of the femoral head (ball) and the acetabulum (socket). This can happen in two distinct scenarios but often it is a combined effect of both bones. Firstly, the femoral head of the hip can have a bump on it making it aspherical or oval. This entity is known as cam-type morphology (shape). Secondly, the acetabulum can be too deep, have more coverage of the femoral head, or faces backwards instead of the usual forward position. These entities are known as pincer-type morphology. In either case, there is premature contact of one bone to another when the person puts their hip in specific positions as demonstrated in the diagram. Oftentimes, these morphologies coexist in the same hip creating an additive effect of abutting against each other in specific motions of the hip.

With persistent or repetitive impinging motion in individuals with cam or pincer morphology over time, the acetabular labrum (hyperlink to labral tear) can get damaged, and additionally, the articular cartilage (white smooth gliding tissue that makes up the joint surface) can gradually wear potentially causing arthritis (see diagram below). The correlation between FAI and arthritis has been proven, however, current efforts are underway in the academic community to investigate the cause of the bone shape in FAI.

Can FAI exist without pain?

While these bony morphologies can be painful in some patients, it is important to recognize that many individuals can have these bony shapes without pain. This concept has been shown through various studies where athletes and individuals from the general population have had their hips examined with various imaging modalities and found to have cam and pincer impingement in the absence of pain.

It is not known which of these individuals will develop symptoms. According to consensus among the experts in hip preservation internationally, individuals with cam or pincer morphology without symptoms should not undergo surgery despite the thought that it could contribute to early arthritis.

The reasons for this consensus are that one is uncertain when in fact arthritis will occur in patients with FAI without pain, whether that arthritis will be painful at that time, if indeed surgery for FAI can truly prevent arthritis, and if it is justified to take the risks of surgery now to reduce the debilitation of arthritis in the future.

How do you diagnose FAI Syndrome?

The diagnosis of FAI syndrome is made with a combination of a history of hip pain, physical examination that reproduces that pain, and imaging of the hip with xrays and in some cases CT scan or MRI to demonstrate the hip morphologies that are associated with FAI (see above).

Hip pain can manifest in different ways and can affect the entire hip girdle, however, usually tends to be in the front of the hip girdle and around the groin. Physical examination is performed by a health care provider taking the hip in various ranges of motion that could cause abutment of the femoral head and the acetabulum as shown in the diagram below.

Hip imaging begins with a weightbearing x-ray of the pelvis, which is very useful and will always be required in the work up of patients with hip or groin pain. Weightbearing x-rays best depict the hip in its most functional position and can detect arthritis based on the joint space between the two bones.

Certain specialized X-ray views are necessary to image FAI.

There are many more radiographic signs that can be helpful in characterizing the architecture of the hip simply on x-rays. More information on these views can be found here.

CT scans and MRI can further show these bony morphologies in cross section as seen below.

At what age does FAI present?

Recent studies have shown that the development of FAI have genetic factors and may develop in individuals participating in high-impact sports during growth (adolescence) as the asphericity of the femoral head typically corresponds to where the growth plate is situated in the femur.

When these morphologies begin to cause pain is still being investigated. There are individuals with FAI that can cope well without pain despite being involved in high-impact athletic activities. Alternatively, repetitive motion or one specific traumatic event could make a person’s hip painful. As such, the age at which FAI presents is variable.

What are the management options for FAI syndrome?

Initially, patients with hip pain in the setting of FAI should be managed conservatively with a period of rest from their inciting activity, followed by symptomatic pain relief by way of different modalities including heat, cold, and/or over-the-counter anti-inflammatory medications. Once the flare up of pain settles, physiotherapy (hyperlink to nonop protocol) with a focus on hip and core specific muscle activation and training has been shown to be a very effective treatment to improve patient symptoms and return them back to their activities of choice.

In some patients, these modalities may not be effective. In such circumstances, surgery may have a role in management. Surgery can be performed with open techniques (with a surgical hip dislocation) or with hip arthroscopy.

Both techniques have been viable options for management, however, in experienced hands, hip arthroscopy has been shown to be successful in improving patient symptoms, returning to sports and other high-impact activities, and perhaps curbing the progression of arthritis.

When is it too late?

Each patient’s situation is different. It is common for middle aged and older adults to present with groin pain. Unfortunately, the rates of arthritis increase with patient age.

Various studies have shown that increasing age (typically above 45 to 50 years) and arthritic changes do not respond well to hip arthroscopy. These patients unfortunately do not have the same improvements as their younger cohorts (younger than 40 years) and have higher rates of conversion to total hip replacement for persistent pain despite hip arthroscopy.

Furthermore, MRI performed in patients with arthritis will show a labral tear 100% of the time based on studies. It is important to note that despite the finding of a labral tear in arthritic hips, the arthritis is the overarching diagnosis and the cause of discomfort rather than a labral tear and hence efforts to treat a labral tear in arthritic hips will not improve the patient’s symptoms.

If a patient has enough arthritic change to preclude hip arthroscopy (see x-ray below) then a change in lifestyle will be suggested including: low impact exercise such as cycling, weight loss (where appropriate), anti-inflammatory medication and if needed injections into the joint (e.g. Hyaluronic acid, Platelet rich plasma or cortisone). When non-operative management has stopped working a hip replacement may be considered.