Layered Approach to the Anterior Knee: Normal Anatomy and Disorders Associated with Anterior Knee Pain.

Anterior knee pain is a common complaint that can be caused by a wide spectrum of disorders affecting the many varied tissues at the anterior knee. The anatomy and pathologic conditions of the anterior knee can be approached systematically by organizing the region into four layers: (a) superficial layer of fat, fascia, and bursae; (b) functional layer composed of the extensor mechanism and patellar stabilizers; (c) intracapsular extrasynovial layer containing the fat pads; and (d) intra-articular layer. The superficial layer is composed of delicate tissues that are predisposed to blunt and penetrating trauma, irritation, and infection. The extensor mechanism forms the functional layer, is responsible for knee extension and patellar stabilization, and is engaged in repetitive movements; overuse disorders dominate in this layer. The fat pads of the anterior knee are discussed collectively as an extracapsular extrasynovial layer, functioning to improve congruence and protect the articular surfaces during motion. Diseases involving the fat pads can be primary or secondary to pathologic conditions in the rest of the joint. The synovial lining and cartilage surface are in the fourth and final intra-articular layer; pathologic conditions are centered around arthritides and internal derangement. Symptoms in the anterior knee may be due to conditions affecting one or more of these interrelated layers. (C) RSNA, 2018