Prefemoral fat pad impingement syndrome: identification and diagnosis.

Fat pad impingement syndrome refers to anterior knee pain caused by hemorrhage, inflammation, fibrosis and/or degeneration of the anterior knee fat pads. Symptomatic impingement of the prefemoral fat pad can be clinically significant but easily overlooked on magnetic resonance imaging, unless looked for. It should be evaluated in patients with persistent anterior knee pain, particulary if accompanied with mechanical symptoms and lack of intra-articular pathology.