Maintaining near-normal synovial membrane stiffness might help interrupt OA-related inflammation. | Shelley PaulsonOsteoarthritis (OA) in horses affects all structures in the joint, including bone, soft tissue, and cartilage, resulting in pain, lameness, and poor performance. Researchers on a new study presented at the 2025 International Cartilage Regeneration & Joint Preservation Society World Congress, held Oct. 11-14, in Boston, Massachusetts, suggest that treating equine joints with a 2.5% injectable polyacrylamide hydrogel (iPAAG) could help preserve joint health by limiting a subtle but important change: stiffening of the synovial membrane.The synovial membrane, a thin layer of tissue that lines the joint capsule, plays a key role in joint health and inflammation. When it becomes thickened or fibrotic, which is common in equine OA, it can contribute to pain, swelling, and progressive cartilage damage. Researchers from Rush University Medical Center, in Chicago, Illinois, led by Markus Wimmer, PhD, and Mohammed AbuAlia, MD, evaluated how OA alters the equine synovial membranes mechanical properties and whether iPAAG treatment could make a difference.The researchers used a well-established experimental model of equine osteoarthritis in the middle carpal (knee) joint. The team assigned 16 horses to receive either intra-articular 2.5% iPAAG or saline. Each horse also served as its own healthy control through a contralateral (opposite) joint that underwent sham surgery, meaning surgeons skipped the carpal fragment procedure in that limb and didnt treat the joint with iPAAG or saline.They collected synovial membrane samples from all study joints and performed rheological testinga method that quantifies how tissues deform with applied stress, or how elastic or stiff they are. Compared to their healthy counterparts, OA joints treated with saline had significantly stiffer synovial membranes than their healthy counterparts. In contrast, joints treated with iPAAG maintained tissue stiffness values close to normal/healthy. In other words, while OA alone made the synovial tissue less elastic and more fibrotic, the iPAAG treatment seemed to counteract that effect, keeping the tissues mechanical properties similar to healthy joints.Take-Home MessageThe authors concluded that maintaining near-normal synovial membrane stiffness might help interrupt OA-related inflammation and degeneration. They said these findings add to a growing body of research supporting iPAAG as a treatment option to improve joint function and comfort.The abstract Shear Stiffness of Equine Synovial Membrane in Osteoarthritis And Response to 2.5% Injectable Polyacrylamide Hydrogel Treatment was part of the International Cartilage Regeneration & Joint Preservation Society World Congress and the proceedings are not yet available.