MRI Findings Consistent with Peripatellar Fat Pad Impingement: How Much Related to Patellofemoral Maltracking?

Peripatellar fat pads are intracapsular extrasynovial adipose cushions that accommodate the changing shape and volume of articular spaces during movement. Variations in bone geometry, passive and active stabilization mechanisms and/or functional demands may lead to peripatellar fat pad abnormalities. While peripatellar fat pads may be affected a variety of conditions such as synovial inflammation, tumor and fibrosis, a mechanical origin should also be considered. Commonly, the clinical term "impingement" is used synonymously in the radiological literature to refer to three distinct entities of structural peripatellar fat pad abnormalities: superolateral the infrapatellar fat pad (Hoffa fat pad) edema, suprapatellar fat pad edema, and prepatellar fat pad edema, implying a mechanical origin of these conditions. The aim of this pictorial review is to describe the normal anatomy of the extensor mechanism of the knee, and discuss the relation of patellofemoral maltracking to the above-mentioned peripatellar fat pad conditions based on current evidence.