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Polyacrylamide hydrogel injection for knee osteoarthritis: results of a 52 week prospective study

      Purpose: Intra-articular (IA) injection of polyacrylamide hydrogel (PAAG) has been suggested as a possible treatment for symptomatic osteoarthritis (OA). Previously IA PAAG has been investigated using 2 injections of 3 ml separated by a month. The primary objective of this study was to evaluate the efficacy and safety of a single injection of 6 ml intra-articular PAAG on knee symptoms in participants with moderate to severe knee OA.
      Methods: Patients with symptomatic (WOMAC A1 ≥2/4 Likert) and radiographic (KL grade 2 to 4) knee OA were consented into this prospective, open-label study. A proprietary 2.5% cross-linked PAAG manufactured by Contura International A/S was used. PAAG contains 2.5% polyacrylamide and 97.5% non-pyrogenic water, with a unique molecular structure that allows normal water exchange with the surrounding tissue without losing shape. PAAG is biocompatible, non-absorbable, non-biodegradable, stable, and sterile. PAAG was provided in sterile, pre-filled 1 ml sealed syringes to be injected intra-articularly with a sterile 21G x 2-inch (0.8 x 50 mm) needle. PAAG is classified as a Class IIb device under Council Directive 93/42/EEC on medical devices. Primary outcome was change in WOMAC pain subscale (normalized to 100 points) after 12 weeks. Secondary outcomes were the WOMAC stiffness and function subscale, Patient Global Assessment of disease impact (PGA) and proportion of OMERACT-OARSI responders. Follow-up time points were 4, 12, 26 and 52 weeks. The protocol for this study was approved by the local Health Research Ethics committee (ref.no: H-19031685), the Danish Health authorities, and was registered at www.clinicaltrials.gov (NCT04179552) before any study related activities. All patients gave informed consent prior to participation, and the study was conducted according to the principles of good clinical practice.
      Results: 49 patients (31 females) received IA PAAG, and 48 and 46 patients completed the 12-week and 52 weeks assessment, respectively. There were statistically and clinically significant reductions in WOMAC pain after 12 weeks (mean change -18.3 points [95% CI: -23.3 to -13.3]; P<.0001) which were sustained at 52 weeks (mean change -20.8 points [95% CI -26.3 to -15.3]; P<0.0001). Similar benefits were found for WOMAC stiffness, physical function, and patient global assessment. After 12 weeks 64.6% of the patients were OMERACT-OARSI responders and this also was maintained at 52 weeks. During the initial 12 weeks, 18 patients reported 23 adverse events; 13 events were related to PAAG treatment (most frequent: arthralgia and joint swelling) and not considered serious. No new PAAG related AEs were observed from 12 to 52 weeks. Three serious adverse events occurred (atrial fibrillation, gastrointestinal pain and cerebrovascular event) all assessed as ‘not related’ to PAAG.
      Conclusions: PAAG can be delivered in a single injection and this non-randomized trial suggests that the good clinical effects at 12 weeks were maintained at 52 weeks in patients with moderate to severe knee OA. These encouraging Results need to be confirmed in controlled studies.