Bone eburnation in rheumatic diseases: a guiding trace in today's radiological diagnosis and in paleopathology.

Bone eburnation is a common anatomical trace of chronic arthropathy. However, its topographical analysis in rheumatic diseases can contribute to knowledge about the latter, by explaining today's diagnosis through radiology as well as by giving an historical perspective through paleopathology. After recalling that eburnated areas can also originate in infectious arthritis, the present analysis consists in a comparison between macroscopic and radiological observations of both osteoarthritis (OA) and rheumatoid arthritis (RA) at an advanced stage. It focuses on the human femoral head because of its demonstrative interest. Two main observations emerge from our study. The eburnated surface is less extensive in OA (where it appears to be essentially linked to the original structure of the hip) and more extensive in RA at an advanced stage (where an additional systemic factor is predominant). The size of the associated osteophytes appears to be inversely proportional to the extent of the corresponding eburnated area. In connection with the OA-RA comparison above, the contribution of the original joint structure to bone eburnation was also illustrated by acromiohumeral eburnation in shoulder OA and by the comparison with dog hip OA. It must also be noted that a femoral head bone remodeling similar on the whole to that of OA can occur in ochronotic arthropathies whose causal chondropathy is due to a genetic defect. Originating in an identified chondropathy, eburnation in ochronotic arthropathy gives us the opportunity to study an OA-type bone remodeling per se as in an experiment supplied by nature and involving a human hip. However, since RA and ochronotic arthropathy are due to a diffuse chondropathy, both may create a similar macroscopic (and thus radiological) eburnation topography.