Experimental model of synovitis/capsulitis in the equine metacarpophalangeal joint.

The research essentially develops a model for studying acute synovitis or capsulitis in a horse’s joint, specifically the metacarpophalangeal joint. In the process, it evaluates the effect of diagnostic or therapeutic procedures on such conditions.

Methodology of the Study

• The test subjects for this study were 5 adult Standardbreds. The researchers induced a condition mimicking acute synovitis/capsulitis by injecting polyvinyl alcohol foam particles into the left front fetlock of horses. The right front fetlock was left untreated, acting as a control for the experiment.
• After inducing the condition, horses were subjected to clinical examination and lameness tests at frequent intervals. Blood samples and synovial fluid samples from both fetlocks were also taken for further testing and measurement.
• The research observed the effects of local diagnostic nerve blocks and intra-articular anesthesia of the fetlock on ensuing lameness. This was done on the second and third day of the experiment.
• Post-test, a macroscopic evaluation was carried out, followed by histologic examination of the fetlock cartilage and capsule.

Findings of the Study

• The study recorded significant changes in synovial fluid variables, including increased TNF-alpha and matrix metalloproteinases values, which are key indicators of acute inflammation.
• It was observed that lameness was reduced considerably after a combination of metacarpal and palmar nerve blocks were applied locally. In contrast, the application of intra-articular anesthesia could only partially block the lameness condition.
• Upon examination post-necropsy, a mild form of chronic inflammation of the synovium and deeper layers of the joint capsule was visible. The injected polyvinyl alcohol particles were found to have been incorporated into the joint capsule.
• No evidence of articular cartilage damage was found during the examination indicating that the model does not seriously affect the horse’s long-term wellbeing.

Conclusions

• The study concludes that the injection of polyvinyl alcohol foam particles successfully induces a transient condition of synovitis/capsulitis in a horse’s fetlock, emulating real joint disorders. This model effectively serves to study the impacts of different diagnostic or therapeutic procedures on such conditions, without causing any adverse effect on the long-term health of horses.