Original comparative model of osteoarthritis in temporomandibular and knee joints

Objectives: Epidemiological studies have shown that osteoarthritis is far less frequent in temporomandibular joint (TMJ) than in other synovial joints. It can be hypothesized that degenerative mechanisms may be delayed or modified in TMJ with regard to the high adaptative potential of the fibrocartilage covering articular surfaces. Numerous models of osteoarthritis studying various criteria and induction procedures have been developed in the TMJ as well as in the knee joint, but none compared concurrently in the same animal the degenerative process in those two joints. The aim of the present study was to create such a comparative model. Methods: Eighteen male New-Zealand white rabbits were used in this study. Twelve animals underwent a single unilateral injection of sodium mono-iodoacetate (MIA) in temporomandibular and knee joints, while six served as controls. They were sacrificed 3, 6, 10, 20, 30 and 90 days after injection and anatomical pieces were prepared for undecalcified histology, after a macroscopic gradation of articular surface changes. Results: MIA was able to induce time-dependent osteoarthritic lesions in both temporomandibular and knee joints. In TMJ, an early cartilage fibrillation occurred within 3 days, but the lesions remained always moderate and surrounded by a hypertrophic reaction of the cartilage. In the knee joint, the lesions were always more severe than in TMJ. They appeared later (10 days) but displayed at once vertical and horizontal splitting. They also progressed faster and more extensively with time, leading to bone exposition of the entire tibial plateau at 90 days. Conclusions: This original comparative approach enlightened the fact that TMJ demonstates a specific response to degenerative changes. The adaptative capacity of the fibrocartilage provided by its fibrous outlayer and undifferenciated mesenchyme influences osteoarthritic evolution by limiting progression and extension of the lesional process.