Instability-induced osteoarthritis in the metacarpophalangeal joint of horses

Objective-To establish an instability model of osteoarthritis (OA) that mim ics the early changes of naturally acquired OA. Animals-6 mature radiographically normal horses. Procedure-The collateral and lateral collateral sesamoidean ligaments were transected in a metacarpophalangeal (MCP) joint in each horse. Lameness exa minations were performed every 7 days after surgery for 8 weeks. Radiograph s were taken immediately before and after desmotomy and 8 weeks after surge ry. Eight weeks after surgery, bilateral MCP joints were grossly evaluated, specimens of articular cartilage were harvested for histologic examination and tissue culture, and synovial membrane was harvested for histologic exa mination. Results-Lameness scores significantly increased over time (mean score of 1. 6 for the 8-week study period). Joint circumference was significantly great er and range of motion significantly less in OA joints, compared with contr alateral joints. Number and size of osteophytes were significantly greater in OA joints. Amount of newly synthesized proteoglycan (PG) was significant ly greater at 18 and 72 hours of cartilage explant culture for OA joints, c ompared with contralateral joints. Total PG content and PG degradation did not differ between OA and contralateral joints. Implications for Human Medicine-This instability model in horses may be use ful in the study of OA in humans. Conclusion-Desmotomy of the lateral collateral and lateral collateral sesam oidean ligaments induced instability similar to that of naturally acquired OA in horses, as documented by lameness, clinical signs of OA, osteophyte f ormation, and erosions of articular cartilage surfaces and score lines in O A joints.