Clinical Presentation

A 63-year-old woman presents with fever, pain in the left leg, and leukocytosis.

(A–C) Magnetic resonance (MR) images of the knee show replacement of the normal fatty marrow signal by diffuse low T1 signal and intermediate to increased proton density and T2 signal. The cortex is intact, without edema, a soft-tissue mass, or periostitis. Minimal normal fatty marrow signal remains in the patella (arr ows).