Femoroacetabular Impingement: Screening and Definitive Imaging

Abstract

Femoroacetabular impingement (FAI) is a recently described entity that occurs when there is impaction of the femoralheadorneckonthelabrumandacetabularrimofthe pelvis secondary to either acquired or developmental abnormality of the femoral head and or acetabulum. 1,2 This abnormal osseous morphology leads to chronic impaction at the extremes of range of motion and subsequent damage of the labrum and articular cartilage. It is critical for the radiologist to have a thorough understanding of this entity because FAI is currently believed to be an important contributor to the early development of osteoarthritis in young patients. However, the natural history of this disorder has not been established, and there is some controversy about the significance of radiologic manifestations of FAI because they can be seen in asymptomatic individuals. The role of the radiologist in the assessment of FAI is 2-fold, screening and definitive evaluation. Screening is usually performed through plain radiography but the findings of FAI may also be recognized on wide field-of-view (FOV) magnetic resonance (MR) imaging (MRI) of the pelvis that is frequently performed for the general evaluation of hip pain. The interpreting radiologist must be sensitive to often subtle findings that may indicate that FAI is responsible or contributing to pain in young patients. Definitive evaluation is usually performed with dedicated imaging of the symptomatic hip by MRI arthrography although noncontrast imaging and, to a lesser extent, computed tomography (CT) have roles in the assessment of suspected FAI.