The Unique Physicochemical Properties of 2.5% Injectable Polyacrylamide Hydrogel (iPAAG) in Joint Lameness Treatment

Introduction

The management of osteoarthritis (OA) in equine patients has seen significant advancements with the introduction of 2.5% injectable Polyacrylamide Hydrogel (iPAAG), commercially known as Arthramid®. This short article explores the unique physicochemical properties of iPAAG, its key features, and the clinical evidence supporting its use in treating joint lameness.

Unique Physicochemical Properties of 2.5% iPAAG

Composition and Structure

Hydrogel Polymer: 2.5% iPAAG is derived from monomers, cross-linked using IL-X technology to form a three-dimensional network.
Stability: Unlike acrylamide, polyacrylamide does not degrade into its monomer form, ensuring stability and biocompatibility.
Water Absorption: The hydrogel exhibits high water absorption, contributing to its viscoelastic properties.

Key Properties – Arthramid is produced under GMP certified conditions ensuring each batch meets rigorous requirements for safety.

Molecular Weight (MW)
Cross-linker Content
Degree of Purity
Porous Size and Homogeneity
Biocompatibility

Mechanism of Action

By targeting the synovium, the primary action of 2.5% iPAAG is the reduction of joint capsule stiffness and modulation of inflammatory responses through improved synovial fluid quality. This is achieved by:

Enhancing tensile strength of the synovial membrane.
Restoring capsular elasticity.
Disrupting the cycle of OA by reducing tissue wear and improving joint function.

Key Features of 2.5% iPAAG

Intra-Articular Administration: Designed specifically for joint applications.
Inert Bioscaffold: Serves as a scaffold for tissue ingrowth without biodegradation.
Sustained Efficacy: Clinical outcomes demonstrate improved mobility and pain relief within 2–4 weeks, continuing over 6-12 months and even longer in some cases.

Clinical Evidence Supporting 2.5% iPAAG

Summary of Key Studies:

Janssen et al (2012)

Study Focus: 12 DIP (coffin) joints assessed through MRI and non-responsive to previous treatments.
Key Findings: 67% of joints were lame-free at 6 months, indicating a positive outcome from treatment.

Tnibar et al (2014a)

Study Focus: Induced osteoarthritis (OA) in the stifle of 4 goats.
Key Findings: 75% (3 out of 4) of goats were lame-free at 7 months post-treatment.
MRI results showed a reduction and subsequent stabilization of OA lesions in treated goats.

Tnibar et al (2014b)

Study Focus: Positive control study comparing Arthramid with Triamcinolone Acetonide (TA) and Hyaluronic Acid (HA) in 40 horses.
Key Findings: 75% of horses treated with Arthramid were lame-free at 6 months, compared to only 35% in the TA/HA group.
Included intra-articular (i.a) analgesia, radiological assessments, and MRI.

Tnibar et al (2015)

Study Focus: 43 horses treated with Arthramid.
Key Findings:
82.5% of horses were lame-free at both 12 and 24 months, indicating long-term efficacy.

Bathe et al (2016)

Study Focus: 18 distal interphalangeal (DIP) joints non-responsive to prior treatments.
Key Findings:
66% of joints were lame-free post-treatment, with an additional 16% showing improvement.

Henrikson et al (2017)

Study Focus: Follow-up of 118 human knee patients.
Key Findings:
Significant improvements in WOMAC scores were observed at 4, 7, and 13 months.
Statistical significance: p<0.0001, indicating a strong positive effect of the treatment.

de Clifford and Lowe et al (2019)

Study Focus: 49 Thoroughbred racehorses with intercarpal joint lameness.
Key Findings:
67.3% were lame-free at 12 weeks, with an additional 16.7% improving enough to continue training.

de Clifford & Lowe et al (2021)

Study Focus: A double-blinded positive control study comparing 2.5% PAAG against TA and HA for middle carpal joint lameness in racing Thoroughbreds.
Key Findings:
This study provides comparative efficacy data, emphasizing the effectiveness of 2.5 iPAAG in a controlled setting.

Ongoing and Future Research

CSU Carpal Chip Study results due late 2025.
Retrospective analysis of the long-term use of 2.5% injectable polyacrylamide hydrogel (2.5% iPAAG) in Thoroughbred racehorse practice: Safety on 701 horses, Efficacy on 214 horses. : The low CMI rate and sustained racing careers in horses in this study support its clinical application for long-term joint management of joint lameness in Thoroughbred racehorses.
Retrospective analysis of the long-term use of 2.5% iPAAG in sport horse practice: safety on 1000 horses, efficacy on 252 horses. This large-scale study demonstrates 2.5% iPAAG’s safety and effectiveness for treating joint-related lameness in sport horses, with minimal complications and high return-to-performance rates.

Conclusion

The 2.5% injectable Polyacrylamide Hydrogel (Arthramid®) represents a promising advancement in the management of joint lameness associated with osteoarthritis in equine patients. Its unique physicochemical properties, combined with robust clinical evidence supporting its efficacy and safety, position it as a valuable tool for veterinarians.

Recommendation for Clinicians

Clinicians should consider incorporating 2.5% iPAAG into their treatment protocols for joint lameness due to its ability to enhance joint function, reduce inflammation, and improve the quality of synovial fluid. The extensive research backing its use underscores its potential to significantly benefit equine patients suffering from osteoarthritis.