A 2.5% Polyacrylamide Hydrogel (PAAG)a was tested for treatment of Osteoarthritis (OA) in a goat model (transection of medial collateral ligament, bisection of medial meniscus and partial-thickness cartilage incisions of medial tibial plateau) with highly encouraging results. The objective was to describe preliminary observations of the mechanisms of action of PAAG in OA joints, based on MRI, pathology and joint capsule elasticity investigations. A randomized controlled study was conducted on an OA knee model in goats: treatment group (intraarticular PAAG), control group (intraarticular saline). Magnetic Resonance Imaging (MRI) was performed prior to surgery, 3, 4, 5 and 7 months post-surgery. Seven months post-surgery, gross pathology and
histopathology, including immunohistochemistry for nerve endings, were performed on both knees. Joint capsule elasticity of the knees was measured in both groups. MRI showed reduction followed by stabilization of OA lesions after PAAG treatment. At gross pathology, PAAG was seen adhering to synovial membrane. Histopathology showed that intraarticular PAAG injection
added to the thickness of the synovial membrane by allowing angiogenesis, collagen and synovial cell increase; PAAG was integrated into the synovial membrane. Nerve endings were intact with normal morphology and
numbers. Joint capsule elasticity investigation showed that treated knees had a higher elasticity when compared to control knees. This study presents preliminary observations of the mechanisms of action of PAAG on OA
joints: (1) Pathology and joint capsule elasticity suggest that PAAG by acting on synovial membrane may reduce overall joint capsule stiffness, a major source of pain in OA. (2) MRI and pathology revealed stabilization of OA lesions in PAAG treated goats, possibly caused by the high viscosupplementation of PAAG.