The groove model of osteoarthritis applied to the ovine fetlock joint

Summary Objective Until now there have been no appropriate models for metacarpophalangeal osteoarthritis (OA), even though OA in this joint is a significant medical and economic problem in horses. A good model would be useful to evaluate progression and treatment of OA, particularly in this joint. Therefore, we translated the canine Groove model to the ovine metacarpophalangeal (fetlock) joint. Method Cartilage surfaces of the metacarpal side of one fetlock joint were surgically damaged (grooved), followed by intermittent forced loading of the experimental joint. After 15 and 37 weeks, cartilage, synovial tissue and subchondral bone were analyzed by the use of macroscopy, histology, biochemistry and micro-CT. Results Technically, the model was difficult to use because cartilage surfaces were very thin. Nonetheless, all macroscopic, histologic, and biochemical cartilage parameters demonstrated adverse changes in chondrocyte activity and matrix integrity. Decreased proteoglycan content suggested slow progression of cartilage degeneration over time, while synovial inflammation diminished. Impaired subchondral bone quality and osteophyte formation were found. Although osteophyte formation was progressive, subchondral bone changes diminished over time. Conclusion The canine Groove model appears to a limited extent transferable to the ovine fetlock joint. However, despite development of adverse changes consistent with early changes of OA, use of the Groove model in the ovine fetlock joint has technical limitations. Using larger animals, such as horses, may significantly improve the technical procedures and with that may provide a more reliable model of metacarpophalangeal OA that is based primarily on intrinsic cartilage damage, appropriate to evaluate the progression and treatment of OA in this particular joint.