A novel scoring system to separate typical OA joint degeneration from non-typical lesions in male rats.

Objective: To develop a novel scoring system to characterize osteoarthritis-related degeneration distinct from spontaneous subchondral bone lesions observed in the tibia and femur of male Sprague Dawley rats.

Method: Knee joints from male rats following 12 weeks of a diet-induced obesity model of osteoarthritis (OA) were assessed. OA histopathological changes (OAHC) were assessed in the knee joints. All scores were evaluated using a modified Mankin score and a modified Osteoarthritis Research Society International histological score. OAHC were divided into 3 categories: (I) Typical OA score evaluating the changes in cartilage structure, cellularity, proteoglycan depletion, and tidemark integrity, (II) A novel Non-typical OA score evaluating cartilage integrity, and the size of local thickening, fragmentation and degeneration along the tidemark and the size and severity of the subchondral bone lesion, and (III) Total OA score comprised of both, the Typical and the Non-typical scores.

Results: Rats exposed to a high fat/high sucrose diet had higher Typical OA score compared to a control group (Chow). Non-typical and Total OA scores revealed no differences in the severity of the lesions between the HFS and the Chow group animals. All scoring systems had excellent intra- and inter-examiner reliability.

Conclusion: The spontaneous bone lesions observed in male Sprague Dawley rats can obscure the effect of the diet-induced obesity if the classical scoring system is used to assess joint degeneration. The newly proposed scoring method provides a reliable method to distinguish classical OA joint degeneration from spontaneous Non-typical lesions occurring in these rats.