Femoroacetabular Impingement refers to the narrowing of space between the neck of the femur and the rim of the acetabulum, due to bony abnormalities. It may occur through one of two ways either through an overgrowth of the femoral neck or bony growth on the acetabular rim. For patients with this issue, the main complaint comes from soft tissue being pinched or compressed in this area.
Normal Anatomy of the Hip 
This hip is considered a ball and socket joint with bony aspects consisting of the acetabulum as the socket and the femoral head as the ball. The socket is further deepened by the labrum, which is a fibrocartilage that lines the rim of the acetabulum. It is important to note that the labrum is wider and thinner on the anterior superior aspect and thicker on the posterior aspect of the acetabulum. The femoral head is a half spherical shape, which is connected to the femoral neck. There is also articular cartilage covering articulating surfaces of both the head of the femur and the acetabulum. The labrum and articular cartilage are important to consider because they may fall victim to shearing forces in the case of an FAI.
Ligaments of the hip connect the head of the femur to the acetabulum and include the
• ligament of the femoral head
• Transverse acetabular ligament
• Iliofemoral ligament
• Pubofemoral ligament
• Ischiofemoral ligament
The Hip is a triplanar joint. Motions of the hip include flexion, extension, abduction, adduction, internal rotation, and external rotation. The hip is important for gait and transferring force from the lower limb to the axial skeleton. In the case of an FAI this transfer of force would be important to note because loading onto the affected limb could cause increased pain.
Cam Impingement is when the head of the femur is abnormally shaped. This impingement is usually the result of a pistol grip deformity, where the head of the femur is not as spherical as it should be. In this scenario, the flattened aspect of the femur is repeatedly forced into the articular cartilage and labrum. With repeated abuse, the articular cartilage can become detached from the subcondral bone and the labrum may be torn. Labral tears are more common on the anterior superior aspect of the acetabulum. Serious deformities of the femur may even lead to an avulsion fracture of the acetabulum. Active males are at a much higher risk of developing this condition than females.
Pincer Impingement is another type of hip impingement. For this condition it is the acetabulum that is abnormally shaped. Usually, the socket aspect of the acetabulum is much deeper than needed. This abnormality is often referred to as a Pincer deformity. This deformity increases the congruency with the femoral head, which puts the labrum and articular cartilage at a greater risk of damage. Pincer impingements are much more common for women than men.
It is important to note that the two types of impingement are not mutually exclusive and that increased force on the opposing bone may lead to the development of osteophytes. If osteophytes form on the opposing bone that may deepen the socket or thicken the neck depending on the structures affected.
Possible Etiology of FAI 
• Pistol grip deformity
• Prior femoral neck fracture
• Prior periacetabular osteotomy
• Legg-Calvé-Perthes disease
• Posttraumatic deformities
• Slipped capital femoral epiphysis
• Acetabular retroversion
• After surgical interventions such as femoral osteotomy
• Posttraumatic deformities
• Coxa profunda (deep socket)
• Protrusion acetabuli
Literature says that there is a much higher prevalence of Femoroacetabular impingement in patients who lead active lives. Literature also coordinates FAI with young patients
Often abnormalities of the hip that are indicative of a FAI limit hip range of motion. The common directions limited in patients with an FAI are hip flexion, adduction and internal rotation. This is congruent with a narrowing of the anterior superior space where the labrum lies. There is a greater approximation of the bone in these positions and as such causes pain through compression of soft tissue structures. Patients usually experience increased groin pain while exercising or completing high impact activities.
Diagnostic tests 
The standard diagnostic test for identifying a FAI is an anterior to posterior x-ray of the patient in standing. This view will show any deformities in the bone and a narrowing of the space between the acetabular rim and the neck of the femur. The film should also be checked for the existence of bony prominences that could restrict movement of the hip joint.
For patients who have more severe issues a MRI may be indicated. The MIR will be much more effective in identifying damage to the labrum and articular cartilage. Some sources even encourage the use of MRI with contrast to better visualize the labrum.
Evaluation and Special Orthopedic Tests 
It is crucial to check passive range of motion for these patients. They are experiencing a bony block that will not allow them to have normal range especially in adduction, internal rotation, and flexion.
Special tests include
- • Anteroposterior impingement test where you place the patient in supine, flex the hip to 90, knee to 90, adduct and internally rotate the leg. A positive sign would be the reproduction of symptoms, whether that is a click or pain.
- • Posteroinferior impingement test where you place the patient in supine with their lower extremities hanging off the table. Then, the therapist extends and externally rotates the hip looking for a comparable sign.
Surgical dislocation of the hip
Periacetabular osteotomy and arthroscopy of the hip which focus of debridement of either the soft tissue or the actual bone.
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