Histological Appearance of the Synovial Membrane after Treatment of Knee Osteoarthritis with Polyacrylamide Gel Injections: A Case Report

Knee osteoarthritis (OA) caused by cartilage damage and synovitis is a painful disease, for which the only effective treatment today is total knee replacement. Polyacrylamide hydrogel (PAAG) is a synthetic non-degradable and non-toxic tissue filler, which allows host cell integration with formation of a scaffold of fibrous tissue inside the gel. A histo-pathological pilot study using this gel for intra-articular injection in rabbit and horse joints has shown that it forms an integrated layer within the upper part of the synovial membrane, and clinical studies of horse joints and human knee joints with OA has shown promising long-term results in pain reduction. It has therefore been the hope that this type of treatment could prolong the time leading up to total knee replacement more effectively than today. The current case report from one of the patients included in the clinical study mentioned above describes, for the first time in a human, how biopsies obtained during meniscectomy after 9 months display the same type of synovial augmentation as seen in horse joints with OA, and that the filler effect from the integrated gel persists in spite of areas with chronic synovitis and microscopic fibrosis.