Osteoarthritis is the leading cause of poor performance in horses; therefore, veterinarians are always looking for novel treatment approaches because many currently available treatments are short-acting and only mild to moderately effective. Recently researchers examined a 2.5% polyacrylamide hydrogel (PAAG) and reported it clinically appealing due to its efficacy, long-lasting effect, and safety.

“This product is a medical device that has received product authorization from the FDA in 2020 for the treatment of osteoarthritis in horses,” said Aziz Tnibar, DVM, PhD, Dipl. ECVS, ACVSMR, ECVSMR, clinical director and head surgeon of The Equine Hospital-Riyadh, Jockey Club of Saudi Arabia, during his presentation at the 2023 American Association Equine Practitioners Convention, held Nov. 29-Dec. 3 in San Diego, California.

He explained that PAAG is a nontoxic and nonimmunogenic (does not produce an immune response) biocompatible biopolymer composed of hydrogel and water with no chemical activity.

“Compared to nonsteroidal anti-inflammatory drugs, corticosteroid anti-inflammatories, and the biologic therapies such as autologous conditioned serum (ACS), PAAG has a completely different mechanism of action, integrating into the synovial membrane, increasing joint capsule elasticity, and providing long-lasting viscosupplementation,”said Tnibar.

During his presentation Tnibar reviewed the following six published clinical studies on PAAG to provide practitioners with the available evidence-based information on this product:

1. In a two-year international multicenter study 43 horses received a single injection of PAAG in one joint and practitioners followed their case progress for two years. “The most important result was that at two years, 82.5% of horses were free of lameness and no side effects were noted,” he said.
2. Another study involved 12 horses with OA in the distal interphalangeal (coffin) joint. These horses were previously treated with triamcinolone (TA, a corticosteroid) and hyaluronic acid (HA) and/or ACS. Six months after PAAG treatment, eight of the 12 horses were free from lameness (67%) and two were improved. Only two horses were not responsive to this therapy.
3. In a controlled study, researchers compared Group 1, made up of 20 horses treated in a single fetlock joint using PAAG, and Group 2, made up of 20 horses treated with 10 mg TA and 20 mg HA. “Horses in Group 1 had significantly improved OA clinical signs compared to horses in Group 2 (P=0.001),” Tnibar said. Specifically, 55%, 65%, and 75% of Group 1 horses were free from lameness at one, three, and six months, respectively—results that were significantly better than those in Group 2, where 15%, 40%, and 35% were nonlame.
4. In a prospective study, researchers used PAAG to treat 18 sport horses that were nonresponsive to other treatments for proximal/distal interphalangeal joint OA. Twelve of these horses returned to full function, three returned to work at a lower function, and only three failed to improve. One of the treated horses had a transient (temporary) adverse reaction following treatment, said Tnibar.
5. Another study involved examining 89 joints in 49 flat racing Thoroughbreds with OA of the carpal (knee) or fetlock joints that had presented with lameness. The number of horses lameness-free at four and 24 weeks was 43% and 62%, respectively, following a single PAAG injection. The researchers showed this improvement to be statistically significant.
6. In a prospective, double-blind, positive control study, scientists compared the efficacy of PAAG and 12 mg TA or 20 mg HA in the middle carpal joints of 31 flat racing Thoroughbreds in full training. They noted similar positive results as in earlier studies because 83% of horses treated with PAAG were lameness-free at six weeks compared to only 27% in TA and 40% in HA horses.

“Treatment with PAAG was statistically superior with therapeutic effects persisting up to 12 weeks,” Tnibar said. Because OA is the most common cause of chronic joint pain and physical impairment in horses, effective therapies are necessary. Based on this clinical data, he added, PAAG has proven itself efficacious with long-lasting effects (up to two years) and safe, with an estimated 0.004% complication rate and only one reported transient complication.

“It is important that the diagnosis (of OA) is accurate, and good injection technique is imperative,” he added. “If PAAG is injected into synovial (joint) membrane instead of intra-articularly, it won’t be as effective.”

Editor’s note: The meeting Proceedings acknowledged in a conflict of interest statement that Tnibar has completed some research funded by Contura International A/S.