Femoral Acetabular Impingement Syndrome

Femoral Acetabular Impingement Syndrome: A motion-related disorder in which abnormal contact occurs between the proximal femur and the acetabular rim that causes pain in the hip or groin (sometimes includes the back, buttock or thigh). Other symptoms such as mechanical symptoms (clicking, catching, or locking), reduced joint mobility (stiffness or restricted range of motion) and joint instability may also occur.

Characterized by a combination of:

• Symptoms
• Clinical Signs
• Relevant imaging findings
• Relevant diagnostic findings (See Diagnosis Section for more information)

The bone morphology in FAIS refers to the abnormal bone shape. An individual can have abnormal bone morphology (such as Cam or pincer morphology) and still be asymptomatic, that is not considered FAIS.

Cam morphology is characterized by loss of normal sphericity at the femoral head-neck junction, most commonly in the anterosuperior region. During hip flexion and internal rotation, the nonspherical femoral head enters the acetabulum and produces shear forces at the chondrolabral junction. This may result in chondrolabral separation, acetabular cartilage delamination, and secondary injury to the labrum.

Pincer morphology refers to excessive or abnormally oriented acetabular coverage. This may be focal, global, or associated with acetabular retroversion. Repetitive contact between the acetabular rim and femoral neck primarily compresses the labrum and may lead to labral degeneration, rim injury, and posteroinferior cartilage damage. Many patients have combined cam and pincer deformities.

The development of symptoms depends not only on osseous morphology, but also on hip motion, activity demands, repetitive loading, and femoral and acetabular orientation. Labral tears and chondral defects frequently coexist with FAIS and may represent progressive consequences of abnormal mechanical contact. Cam morphology is also associated with an increased risk of hip osteoarthritis, although many individuals with abnormal morphology remain asymptomatic.

While some patients remain asymptomatic with abnormal bone morphology, there are certain risk factors which can increase the risk of developing symptoms. There is evidence to suggest a genetic component to the development of FAIS. Repetitive impingement can cause progressive injury and progression of abnormal morphology, increasing the risk in high performance athletes. Another consideration is that cam morphology develops mainly during skeletal maturation, so children and adolescents who participate in sports are at added risk.