Femoro-acetabular impingement: what the general radiologist needs to know

Femoro-acetabular impingement (FAI) is a common condition in young active subjects, which can lead to the development of early osteoarthritis if not correctly diagnosed. Imaging evaluation of FAI, mainly based on plain film and magnetic resonance evaluation, must be performed according to precise guidelines and is fundamental for reaching a final diagnosis. The purpose of this paper is to provide a clinical and radiological overview of FAI by describing the most common clinical tests, the imaging techniques used in the diagnosis, and the main radiological signs that may be encountered.