Clinical and Histologic Evaluation of Polyacrylamide Gel in Normal Equine Metacarpal/Metatarsal-Phalangeal Joints

Introduction: Polyacrylamide hydrogel (PAHG) is being developed to treat osteoarthritis in horses. Prior to application in osteoarthritic joints, evaluation in normal joints is indicated. The objectives of this study are to evaluate the clinical, cytologic, histologic and metabolic effects of PAHG in normal fetlock joints.

Materials and Methods: This study is an in vivo controlled study utilizing six horses that had four fetlocks assigned to a 7, 28, 56 day or control group. Synovial fluid was collected prior to administration of 2.5 mL of 4% PAHG and again at the completion of the study for macroscopic, cytologic, and cartilage metabolism evaluation. The completion of the study included gross and histologic examination of the cartilage and synovial membrane.

Result: There was a small but significant (p = 0.0242) increase in cell count in the synovial fluid at 7 days. There were significant changes in the synovial membrane histology score (p = 0.0277) as a result of hypertrophic synoviocytes. Biomarkers indicated a small increase in cartilage turnover 7 days after PAHG administration. The PAHG was visible on the surface of the synovium at 7 days and PAHG appeared in the interstitial spaces of the synovium and intracellular at days 28 and 56.

Discussion/Conclusion: Data from this study provide information about tolerance and disposition on intraarticular PAHG in a normal fetlock joint during a 56-day study. There were no major or permanent detrimental effects seen with the administration of PAHG in normal joints.

Acknowledgement: Study funded by Nucleus Regenerative Therapies.

No conflict of interest has been declared by the author(s).