Case 2, Lower Limb Anomaly or Pathology         (Return to Case List)
This patient presented to the Emergency Room with a badly sprained and swollen right ankle. A plain-film Xray of the ankle is shown below. What do you think the yellow arrow points to? Click on the drop-down arrow to see what it is.



The Emergency Room physician thought this might represent an avulsion of the lateral malleolus, but it's edges seemed too smooth to be those of a recent fracture. She recommended the patient see an orthopaedist for treatment of the sprain, and she asked to be advised of the orthopaedist's evaluation of the Xray. The patient saw Dr. James Penna, Chair of Orthopaedics and Chief of Sports Medicine at Stony Brook University Renaissance School of Medicine. Dr. Penna immediately identified the object to which the yellow arrow points as an Os Subfibulare, a smooth-edged bony nodule just inferior to the tip of the lateral malleolus that may form as an normal variant accessory bone or as the result of an old ankle sprain that indeed did avulse the tip of the lateral malleolus. Since the patient had no history of a previous ankle sprain, Dr. Penna opted for accessory bone. Regardless of cause, os subfibulare can sometimes cause ankle pain that requires operative treatment. In this case it was an incidental finding.