Instability-induced osteoarthritis in the metacarpophalangeal joint of horses.

The research article details a study conducted on six horses, aiming to establish an instability model of osteoarthritis (OA) that reflects the initial changes seen with naturally occurring OA. The findings suggest that the model successfully induced instability in horses comparable to naturally acquired OA and could be useful in studying human OA.

Study Design and Methods

• The researchers selected six mature horses with no radiographic abnormalities.
• The horses underwent a surgical procedure (desmotomy) that disrupted the collateral and lateral collateral sesamoidean ligaments in a metacarpophalangeal (MCP) joint. This procedure aimed to simulate the joint instability seen in early OA.
• Post-surgery, the progress was monitored by conducting lameness evaluations every week for eight weeks. Radiographs were captured immediately before and after the desmotomy and eight weeks post-surgery for a detailed examination of the joint condition.

Results and Observations

• There was a significant increase in lameness scores over time, with an average score of 1.6 for the eight-week study period, suggesting increasing discomfort or difficulty in movement post-procedure.
• The circumferences of the OA joints were significantly larger, and the range of motion was notably lower compared to the non-operated joints, indicating joint swelling and reduced flexibility, respectively.
• There was a considerably higher number and size of osteophytes (bony growths) in the OA joints. Increased osteophyte formation is a common symptom of OA.
• The amount of new proteoglycan (PG), a key component of cartilage, was significantly higher in the OA joints at 18 and 72 hours of cartilage explant culture. This could denote an attempt by the joint to recover from the induced instability. However, the total PG content and rate of PG degradation did not differ between the OA and contralateral (non-operated) joints.

Conclusion and Implications

• The procedure of ligament desmotomy successfully replicated the instability seen in naturally acquired OA in horses, as observed through lameness, visible OA symptoms, osteophyte formation and changes in articular cartilage.
• This model could be beneficial in studying the onset and progression of OA in humans, potentially contributing to improved understanding and treatment strategies for OA.