Figure 5. Sarcomatous degeneration of bone in a 57-year-old man with right knee pain that did not respond to physical therapy. Anteroposterior radiograph of the knee shows sclerotic lesions typical of multifocal osteonecrosis (arrowheads). Destruction of the lateral cortex of the proximal tibia (arrow) is indicative of sarcomatous degeneration, a finding that was confirmed at MR imaging. This patient was appropriately referred to the Orthopaedic Oncology Clinic.