What disease process is causing this dog's lesion?
A 2-year-old German shepherd is presented for evaluation of a subcutaneous nodule over the olecranon region of the elbow. The nodule is extremely firm, and material obtained through fine-needle aspiration is gritty and chalky white. Unstained, with the microscope condenser lowered, the material appears refractile. After staining with Wright's-Giemsa stain, little is apparent except for a stippled background, small numbers of red blood cells, and occasional macrophages-a few that are multinucleated.
What is the most likely diagnosis for this lesion?