Everything you need to know about this novel intra-articular therapy
Osteoarthritis (OA) is one of the more serious performance-altering and potentially career-ending maladies to affect horses. Equine practitioners and researchers make great efforts to seek out effective treatments. What started decades ago as palliative care using intra-articular corticosteroid (triamcinolone acetonide, or TA) and/or hyaluronic acid (HA) intra-articular injections has more recently transformed into therapeutic use of regenerative therapies with biologic agents such as IRAP (interleukin-1 receptor antagonist protein), platelet-rich plasma, and stem cells within a joint.
A new treatment approach has come to the forefront that holds promise for improving the health and comfort of ailing joints: polyacrylamide gel, or PAAG, which is designed to restore joint capsule elasticity and synovial (joint) fluid viscosity and improve lubrication. In this article we’ll review the mechanisms of action and science behind two types of PAAG on the market: 2.5% and 4%.
What Is 2.5% PAAG?
Florent David, DVM, MS, Dipl. ACVS, ECVS, ACVSMR, ECVSMR, ECVDI, associate and senior surgeon at the Equine Veterinary Medical Center, in Doha, Qatar, has been part of the vanguard of practitioners using PAAG regularly to treat OA in sport and racehorses. He describes 2.5% PAAG as a nontoxic gel that retains viscoelastic properties through cross-linking technology. He says the gel integrates with water molecules and surrounding tissue to form a bioscaffold, and that the material incorporates into the synovium (the joint lining) about four weeks post-injection and can persist up to two years in OA-affected and control joints. In his experience, he adds, orthopedic shoeing and modified exercise programs help maximize the duration of improvement.
“I see many cases injected on multiple occasions with corticosteroids yet with far too short an interval between injections,” says David. “Response to corticosteroids often lessens or fails to achieve improvement by the time I see the horse. I prefer to catch joint damage early in its course to avoid having to use other intra-articular therapies. In some instances it may be appropriate to use PAAG joint injections in horses as young as 1 to 4 years old, depending on breed and activity. Early implementation of PAAG is particularly appropriate for horses where a conformational issue has been identified as a ticking time bomb for joint degeneration.”
He adds that combining orthopedic shoeing and PAAG can help stave off joint degeneration in young horses entering an intense sport with conformation faults that would otherwise result in unmanageable joint damage.
“PAAG is beneficial for established OA or its precursor and early stages,” David says. “Based on the study results with 2.5% PAAG (TheHorse.com/183011), 60-70% of the cases returned to soundness after one PAAG injection for the joints tested—coffin, pastern, fetlock, and knees. It seems to be slightly less efficient in managing severe or chronic cases, with only 10% reduction in the chance of returning horses to soundness. As yet, we don’t have a large-scale study comparing the outcome at various stages of osteoarthritis.”
He says he likes to use PAAG to provide a therapeutic effect when horses have three to four weeks before their next competition or when corticosteroids are contraindicated for joint or metabolic health or banned due to competition testing requirements. “Because this medication needs time to elicit its benefit in a joint, it is not appropriate to use it at the last minute in an attempt to push a lame horse through a competition that might risk a more serious injury,” he stresses.
Label directions recommend transitioning horses back to work slowly over two weeks to allow time for the gel to incorporate into the synovium and to reduce the chance of a joint flare. If a veterinarian injects a joint with 2.5% PAAG for preventive or maintenance purposes, David says the horse might only need 48 hours of rest following
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