In the AP and lateral views of the left lower leg and knee, we can see a well-circumscribed lesion on the medial aspect of the proximal tibia.  This osseous protuberance arises from the external surface of the tibia and contains medullary marrow and cortex that are continuous with those of the parent bone.  A cap of hyaline cartilage covers the tip of this lesion.  The cap is thin and fairly well defined which is consistent with a benign lesion.  Malignant lesions will have a thicker cap with poor definition and irregular calcifications.  The base of this lesion is broad; however, some lesions of this group may be pedunculated.