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Sustained symptom relief and safety over five years following a single intra-articular injection of 2.5% polyacrylamide hydrogel in patients with knee osteoarthritis
H. Bliddal1, J. Beier2, A. Hartkopp3, P.G. Conaghan4, M. Henriksen5
- Department of Clinical Medicine, The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, University of Copenhagen, Denmark. henning.bliddal@regionh.dk
- Gigtdoktor, Odense, Denmark.
- A2 Rheumatology and Sports Medicine, Holte, Denmark.
- Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds & NIHR Leeds Biomedical Research Centre, UK.
- Department of Clinical Medicine, The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, University of Copenhagen, Denmark.
CER19414
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PMID: 41779591 [PubMed]
Received: 15/10/2025
Accepted : 23/12/2025
In Press: 04/03/2026
Abstract
OBJECTIVES:
A randomised controlled trial (RCT) demonstrated that a single 6 mL intra-articular (IA) injection of polyacrylamide hydrogel (iPAAG) provided comparable efficacy and safety to hyaluronic acid over one year in patients with moderate-to-severe knee osteoarthritis (OA). This study reports the longer-term outcomes of iPAAG.
METHODS:
In this long-term extension of the RCT (ClinicalTrials.gov Identifier: NCT04045431), participants treated with IA 2.5% iPAAG were followed for changes from the RCT baseline in WOMAC pain, stiffness, and physical function subscales (0–100), as well as patient global assessment (PGA) of OA impact. Safety was monitored throughout the extension study.
RESULTS:
Of 119 participants initially treated with iPAAG, 91 (47 men) entered the extension, and 58 completed 5 years of follow-up. At year 5, WOMAC pain improved by a mean of -16.2 points (95% CI: -20.0 to -12.4; p<0.0001). Similar improvements were observed across other WOMAC domains and PGA. Between years 1 and 5, 79 adverse events (AEs) were reported in 47 participants (51.6%), none considered related to iPAAG.
CONCLUSIONS:
A single IA injection of iPAAG was associated with sustained improvements in pain and function, with a favourable safety profile maintained through 5 years. These observational data support iPAAG as a promising long-acting, non-surgical treatment option for knee OA.
