Femoroacetabular impingement (FAI) is one of the most common reasons of hip pain in the young adult. It consists of a mechanical conflict between the femoral head and the acetabulum, influenced by two factors: an anatomical predisposition of the hip and an external condition, which in our environment would be the practice of certain type of sports.

The hip is a ball and socket joint that admits very little alterations in its normal anatomy to be able to offer an adequate function. FAI has been associated with early development of hip osteoarthritis, leading to symptoms like stiffness and pain.

Normal Hip

Types:

Two types of FAI have been described:

Cam type FAI is a consequence of the presence of an osseous bump in the femoral neck-head junction, which is responsible for a mechanical block during the normal motion of the head inside the acetabulum.

Pincer type FAI presents with an impact of the rim of the acetabulum against the head-neck junction, due to overcoverage of the femoral head by the roof of the acetabulum.

Most cases of FAI are a combination of both types; therefore, they present with a mixed pattern of injuries.

The labrum is an important structure of the hip that works as a “meniscus” to provide a seal of the joint to allow an adequate function.

Femoroacetabular impingement

FAI and sports:

FAI is related with continuous activity of the hip in flexion and inner rotation, as in case of sports like football, basketball, rugby, tennis; running consists of a repetitive impact sport to the hip, hence it is included within this group. Regardless the fact of presenting with a cam or pincer deformity, it is common that many sports produce a mechanical conflict or impingement due to this exercise “exceeding” the normal function of the hip (ballet, gymnastics, track and field, martial arts, etc).

Symptoms:

For most patients, it is difficult to precise where pain over the hip comes from, given the fact that it presents with a wide variety of patterns, themselves hard to locate exactly. In most cases, it is localized over the groin area and the “C” of the hip, which includes also the lateral and the back of the trunk and leg junction.

The symptoms of FAI can start off as early as during adolescence, however they usually become recognizable after the 3^rd or 4^th decade of life (between the age of 20 and 30); sometimes, a serious damage to the joint is already established after the age of 40.

At first, the pain is mild and tolerable, mostly associated with sports or certain held positions of the leg. Usually, it is felt as a kind of pressure over the fore part of the trunk-leg junction i.e. the groin area. Pain presents in episodes that subside with rest or physiotherapy, or even for no specific reason. Anti-inflammatories may also relief the symptoms partially, however, they don’t solve them for good. Clicking and stiffness are also commonly associated with the clinical presentation of FAI. To this point, many wrong diagnoses are given like psoas tendinitis, pubalgia (pubic osteopathy) and even problems that have nothing to do with the hip like inguinal hernia or testicle problems in males.

There are certain patterns that mean to compensate FAI, i.e. a group of symptoms that are a consequence of the offset of the compromised function of the hip. These are, amongst others, the lower back pain, the pubic osteopathy and the sacroiliac pain.

Over time, pain becomes stronger and associates with more simple activities. In this situation, articular damage might be already settled.

Diagnosis:

Plain X rays are critical for evidencing the anatomic features of cam and pincer type FAI. For that, special views are performed to better show the deformities of the hip (AP pelvis and 45º Dunn view). The X rays are also useful to rule out the presence of significant osteoarthritis or “joint wearing”, given the fact that this conditions the treatment to follow.

Despite that nowadays it is considered less important than years ago to diagnose FAI, magnetic resonance (MR) allows for ruling out associated problems and evaluating the labrum. The injection of contrast (gadolinium) inside the joint is not considered essential any more for diagnosing FAI, and must be saved for unclear cases. The labrum may present with tears in the MR studies even in patients who don’t have any pain or catching, hence the correlation of these studies with the patient’s symptoms is critical.

CT scan is valuable in the evaluation of the general anatomy of the hip, especially the 3D reconstructions for planning a surgery.

Treatment:

The initial treatment of the symptoms includes the use of anti-inflammatories and physiotherapy. In most cases, if the impingement is settled, these allow only for a temporary relief. Intraarticular injections may help in treating the symptoms as well as confirming the diagnosis: when this injection offers relief, supports the presence of an intraarticular problem (i.e. FAI in this case). In contrast, extraarticular conditions will come up with no modification after the injection. In occasions, intraarticular injections with long-lasting effect anti-inflammatories can provide a relatively long relief. This technique can be done either with the use of X rays or ultrasound.

The use of all these non-operative treatments may relief the pain during some time; nevertheless, in cases of established FAI, an accurate diagnosis is mandatory to be able to achieve a final treatment as soon as possible.

Hip arthroscopy:

Hip arthroscopy consists of a minimally invasive technique that allows for correcting anatomic “deformities” associated with FAI by using a special camera inside the joint and several instruments especially designed for this. In addition, labrum and articular cartilage injuries can be also treated. This camera shows directly the hip joint so that any kind of problem within the tissues can be detected and treated through only 2 or 3 additional accesses or portals (incisions of only a few millimeters long). Arthroscopic surgery avoids open surgery, offering advantages in terms of postoperative pain and recovery.

Hip arthroscopy is an effective tool for resecting cam and pincer deformities, as well as repairing structures like labrum and articular cartilage. Indeed, this technique requires a specific and long training, and different studies have shown that the results of the surgery depend highly on the expertise of the treating surgeon. The aim of the arthroscopy is, firstly, to treat the symptoms, restoring patient’s normal lifestyle. In addition, and given the fact that FAI has been associated with hip osteoarthritis in young patients, another objective would be to prevent the outwearing of the joint and the need for a hip replacement.