The differential diagnosis of geodes.

Lytic lesions close to or at the articular margins are secondary to a wide range of etiologies, including osteoarthritis, rheumatoid arthritis, hemophilic arthropathy, and crystal deposition disease as well as tumor and tumor-like conditions. In many cases the features of these "cysts" are distinctive, and the purpose of this article is to outline the characteristic hallmarks in some of the more frequently encountered arthropathies.