Osteomyelitis of the patella

(A) Axial T1-weighted image demonstrates signal changes and cortical interruption overlying the anterior and lateral patella. Patellar osteomyelitis is present (long arrow). Incidental note is made of an enchondroma (asterisk). (B) Axial short tau inversion recovery (STIR) image demonstrates high signal edema in the marrow of the anterior and lateral patella with overlying soft tissue loss representing osteomyelitis (long arrow). A small knee joint effusion is also present (arrowheads). (C,D) Pre- and postcontrast axial images demonstrate enhancement in the distribution of edema in the patella and overlying soft tissues. Patellar osteomyelitis is present in panel D (long arrow).