Magnetic resonance imaging of variants of the knee.

Magnetic resonance imaging has become the imaging modality of choice for evaluation of internal derangements of the knee. Anatomical variants are often an incidental finding on these examinations. Knowledge and recognition of variants is important, not only to avoid misdiagnosis but also to avoid additional imaging and over-treatment. This pictorial essay provides an overview of variants encountered during a review of 1,873 magnetic resonance imaging examinations of the knee. Emphasis is laid on these variants that are clinically important.