The patient went on to have a biopsy at the time of surgery.

Histology

MICROSCOPIC DESCRIPTION: The sections show a mildly cellular cartilaginous tumor. It forms lobules and nests. No prominent myxoid change is seen. The tumor is seen in the medulla. The rounded nests are surrounded by lamellar bone and mineralized matrix. There is no breach of the bone into the soft tissue. The chondrocytes show no significant nuclear atypia. Rare binucleated forms are seen. No abnormal mitoses are identified. There is no necrosis. At the fracture site, there is enchondral ossification with new bone formation and adjacent granulation tissue. The features are those of enchondroma. There is no evidence of malignancy. 

DIAGNOSIS: Enchondroma.