The sesamoids generally appear as small ovoid bones adjacent to articulations or at sites where tendons are angled about osseous surfaces. At either location they participate in joint afflictions, the pattern of abnormality being remarkably constant and predictable. Sesamoids may demonstrate osseous erosion in rheumatoid arthritis, bony proliferation or "whiskering" in rheumatoid variants, joint space narrowing and bony ankylosis in septic arthritis, and eburnation and osteophyte formation in osteoarthritis and diffuse idiopathic skeletal hyperostosis. These changes become particularly important when they occur in the absence of significant adjacent articular disease. In these instances, recognition of sesamoid abnormalities allows accurate radiographic diagnosis.