The OARSI histopathology initiative – recommendations for histological assessments of osteoarthritis in sheep and goats

Objective: Sheep and goats are commonly used large animal species for studying pathogenesis and treatment of osteoarthritis (OA). This review focuses on the macroscopic and microscopic criteria for assessing OA in sheep and goats and recommends particular assessment criteria to assist standardization in the conduct and reporting of preclinical trials of OA. Methods: A review was conducted of all published OA studies using sheep and goats and the most common macroscopic, microscopic, or ultrastructural scoring systems were summarised. General recommendations regarding methods of OA assessment in the sheep and goat have been made and a preliminary study of their reliability and utility was undertaken. Results: The modified Mankin scoring system is recommended for semiquantitative histological assessment of OA due to its already widespread adoption, ease of use, similarity to scoring systems used for OA in humans, and its achievable inter-rater reliability. Specific recommendations are also provided for histological scoring of synovitis and scoring of macroscopic lesions of OA. Conclusions: The proposed system for assessment of sheep and goat articular tissues appears to provide a useful versatile method to quantify OA change. It is hoped that by adopting more standardised quantitative outcome measures, better comparison between different studies and arthritis models will be possible. The suggested scoring systems can be modified in the future as our knowledge of disease pathophysiology advances.