Osteonecrosis is common and represents loss of blood supply to a region of bone. Common sites affected include the femoral head, humeral head, knee, femoral/tibial metadiaphysis, scaphoid, lunate, and talus. Symptomatic femoral head osteonecrosis accounts for 10,000-20,000 new cases annually in the United States. In contradistinction, metadiaphyseal osteonecrosis is often occult and asymptomatic. There are numerous causes of osteonecrosis most commonly related to trauma, corticosteroids, and idiopathic. Imaging of osteonecrosis is frequently diagnostic with a serpentine rim of sclerosis on radiographs, photopenia in early disease at bone scintigraphy, and maintained yellow marrow at MR imaging with a serpentine rim of high signal intensity (double-line sign) on images obtained with long repetition time sequences. These radiologic features correspond to the underlying pathology of osseous response to wall off the osteonecrotic process and attempts at repair with vascularized granulation tissue at the reactive interface. The long-term clinical importance of epiphyseal osteonecrosis is almost exclusively based on the likelihood of overlying articular collapse. MR imaging is generally considered the most sensitive and specific imaging modality both for early diagnosis and identifying features that increase the possibility of this complication. Treatment subsequent to articular collapse and development of secondary osteoarthritis typically requires reconstructive surgery. Malignant transformation of osteonecrosis is rare and almost exclusively associated with metadiaphyseal lesions. Imaging features of this dire sequela include aggressive bone destruction about the lesion margin, cortical involvement, and an associated soft-tissue mass. Recognizing the appearance of osteonecrosis, which reflects the underlying pathology, improves radiologic assessment and is important to guide optimal patient management.

A 43-year-old man presented to the Department of Orthopedic Surgery at the Mayo Clinic Florida with a 2-year history of left knee pain. The patient described the pain as an aching, squeezing, and throbbing pain that worsened when he stood or walked but improved when he sat. Indeed, sitting was noted to be the only position that provided the patient with symptomatic relief. The pain awakened him at night and was associated with a subjective feeling of progressive weakness in his leg. Multiple nonoperative measures failed to improve the patient's symptoms. The patient's past medical history was significant, with a diagnosis of Maffucci syndrome having been made when he was 1 year old. The patient had undergone numerous surgical procedures over the course of his lifetime. Most significantly, he had received a previous diagnosis of and treatment for malignant transformation of cartilaginous lesions involving the cervical spine and left elbow.

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