Zygapophyseal articular surface cortical disruption noted radiologically in RA is at variance with the perception that it is an axial joint-sparing (cervical vertebrae excepted) disorder. However, the reliability of such radiologic assessment has been questioned. Direct visual examination of the zygapophyseal and costovertebral joints (of individuals with documented RA, spondyloarthropathy, diffuse idiopathic skeletal hyperostosis and normal controls) allowed these radiologic perceptions to be tested and placed in perspective. Articular surface cortical disruption/discontinuity was actually found to take two forms, indistinguishable by standard X-ray technique: 1. fronts of resorption, with reactive new bone formation; 2. exposed bare trabeculae, secondary to a 'wearing away' abrasion process. Zygapophyseal and costovertebral erosions were only found in skeletons of individuals with spondyloarthropathy, whereas the abrasion-related phenomenon was especially prevalent in RA and in normal controls. Inability to radiologically distinguish abraded or 'worn away' lesions from erosions explains past radiologic confusion. Radiologic evidence of zygapophyseal and costovertebral joint surface disruption/discontinuity does not appear specific for erosive disease.