An experimentally induced osteoarthritis model in horses performed on both metacarpophalangeal and metatarsophalangeal joints: Technical, clinical, imaging, biochemical, macroscopic and microscopic characterization.

Osteoarthritis is a common cause of pain and economic loss in both humans and horses. The horse is recognized as a suitable model for human osteoarthritis, because the thickness, structure, and mechanical properties of equine articular cartilage are highly comparable to those of humans. Although a number of equine experimental osteoarthritis models have been described in the literature, these cases generally involve the induction of osteoarthritis in just one joint of each animal. This approach necessitates the involvement of large numbers of horses to obtain reliable data and thus limits the use of this animal model, for both economic and ethical reasons. This study adapts an established equine model of post-traumatic osteoarthritis to induce osteoarthritis-associated lesions in all 4 fetlock joints of the same horse in order to reduce the number of animals involved and avoid individual variability, thus obtaining a more reliable method to evaluate treatment efficacy in future studies. The objectives are to assess the feasibility of the procedure, evaluate variability of the lesions according to interindividual and operated-limb position and describe the spontaneous evolution of osteoarthritis-associated pathological changes over a twelve-week period. The procedure was well tolerated by all 8 experimental horses and successfully induced mild osteoarthritis-associated changes in the four fetlock joints of each horse. Observations were carried out using clinical, radiographic, ultrasonographic, and magnetic resonance imaging methods as well as biochemical analyses of synovial fluid and postmortem microscopic and macroscopic evaluations of the joints. No significant differences were found in the progression of osteoarthritis-associated changes between horses or between the different limbs, with the exception of higher synovial effusion in hind fetlocks compared to front fetlocks and higher radiographic scores for left fetlocks compared to the right. This model thus appears to be a reliable means to evaluate the efficacy of new treatments in horses, and may be of interest for translational studies in human medicine.