polyacrylamide hydrogel in knee osteoarthritis

Osteoarthritis (OA) affects 7.6% of the population, with the knee being the most commonly involved joint (1).

Arthrosamid® is a non‑absorbable, biocompatible polyacrylamide hydrogel licensed for intra‑articular use in knee OA (1,2):

• hydrogels have a wide range of applications in surgery and have been used for over 20 years in specialties such as ophthalmology, urology and plastic and aesthetic surgery, where they have an established safety profile
  • has been used for various indications such as bulking for stress urinary incontinence and soft tissue augmentation
• Arthrosamid is reported as being a non-absorbable, non-biodegradable, transparent, hydrophilic gel consisting of 2.5% cross-linked polyacrylamide and 97.5% sterile non-pyrogenic water
  • unique molecular structure allows normal water exchange and integration with the surrounding soft tissue without losing its volume
  • manufacturers recommend a single dose of 6 ml for the treatment of Kellgren–Lawrence grade II OA and above
  • given that polyacrylamide is not absorbed and remains in situ after injection, prophylactic antibiotics are administered before the procedure to minimise the risk of an infection
• exact mechanisms by which polyacrylamide hydrogel injection alleviates symptoms in patients with knee OA are not currently fully understood (1,2)
  • based on preclinical evidence, it has been proposed that its principal mechanism of action involves the synovium
  • is proposed that polyacrylamide hydrogels may modify the immune response in OA by acting as a barrier between inflammatory cells and the synovial lining of the joint cavity, thereby distancing inflammatory cells and slowing their cellular signalling
  • over time, proliferating synovial cells migrate into the gel causing the synovial layer to undergo hyperplasia and subsequently thicken
    • occurs within the deeper parts of the synovial membrane resulting in a dense fibrous tissue and occasionally loose fibro-fatty tissue
    • in animal models, a synovial lining has been shown to re-establish superficial to the integrated polyacrylamide hydrogel at the joint cavity interface through proliferation of synovial cells
  • in equine OA, preliminary observations on the mechanisms of action of intra-articular polyacrylamide hydrogel support a mechanical effect through integration into the synovial membrane, an increase in joint elasticity possibly reducing overall joint capsule stiffness, and provision of lasting viscosupplementation which contributes to protecting articular surfaces (3)
    • no effects on pro-inflammatory cytokines have been observed
    • studies also suggest that these positive effects occur in the absence of intra-articular neurotoxicity or fibrosis

Study findings suggest that polyacrylamide hydrogel improves knee OA symptoms (1):

• however, limitations in study quality, mechanistic understanding and long–term evidence preclude recommending routine clinical use, and it should therefore be used cautiously

Reference:

1. Farhan-Alanie MM, Brown S, Wright K, Snow M. Efficacy of novel polyacrylamide hydrogel injection for osteoarthritis. Knee. 2026 May 18;62:104492.
2. Bliddal H et al. Effectiveness and safety of polyacrylamide hydrogel injection for knee osteoarthritis: results from a 12-month follow up of an open-label study. J Orthop Surg Res. 2024 May 2;19(1):274.
3. Tnibar A. Intra-articular 2.5% polyacrylamide hydrogel, a new concept in the medication of equine osteoarthritis: A review. J Equine Vet Sci. 2022 Dec;119:104143.