One of the most common causes of lameness in horses is osteoarthritis (OA). Horse owners across the country spend countless hours and wages trying to provide their horses with effective pain management tools in hopes of providing prolonged comfort and happiness – whether in the pasture or in the show pen.
For years, the only known joint injection protocol with numerous studies to support applications for horses at all career checkpoints (training, competition, retirement) has been hyaluronic acid. Hyaluronic acid (HA) injection is an intra-articular injection into the joint. It is popular with high-level competition horses and is acceptable for use in racehorses.
“However, there is currently a model rule that says you cannot have intra-articular injections in the 14 days before a race,” says Dr Mary Scollay, head of science for the Road Safety and Integrity Authority (HISA). Anti-Doping and Drug Control Program. “Not all states have adopted this, but it is the ARCI Model Rule.”
However, due to the expense of HA injections to purchase, there has been a push for animal science companies to produce a similar effect. Enter the non-degradable synthetic gel, polyacrylamide hydrogel.
Two of the most common types of injectable synthetic hydrogels are marketed in the United States as Arthramid Vet and Noltrex Vet.
Noltrex Vet is a 4% polyacrylamide (pAAm) hydrogel that is marketed to target “a root cause of joint pain by physically reducing friction.” According to the Noltrex Vet website, the manufacturer claims the gel coats the horse’s joint cartilage with a protective layer of lubrication while reducing friction. The gel also forms a protective/lubricating layer on the joint surfaces and helps to restore and maintain the horse’s healthy joint function.
Arthramid Vet is a 2.5% cross-linked pAAm gel. According to the Contura Vet website, the manufacturer claims that the gel adheres to the synovial lining through the gel’s ability to exchange water molecules. Then, the gel integrates into the synovial mucosa over a period of 14 days. It is labeled for the management of all stages of non-infectious osteoarthritis and degenerative joint disease in horses. The difference with Arthramid Vet, according to the website, is that the injection becomes completely integrated into the surrounding tissues, making it long-lasting.
Numerous studies have shown that pAAm hydrogel has a lubricating ability that decreases cartilage friction, thus helping to promote more pain-free movement for healthy and degraded cartilage. In a study presented at the 2019 American Association for Equine Practitioners Convention by Dr. Scott McClure, Dipl. ACVS and owner of Midwest Equine Surgery & Sports Medicine in Boone, Iowa. Dr. McClure and his research team evaluated the effects of pAAm hydrogel on tissue structure in the joints of six healthy horses. They also tested the gel on 28 horses with natural osteoarthritis.
The first six horses were found to have no adverse effects following administration of the pAAm hydrogel, and the hydrogel was still visible on the lining of the joint capsule when viewed 28 and 56 days after injection.
Of the 28 horses with osteoarthritis, the injection showed positive numbers, including:
23 horses showed improvement based on study criteria at day 45 post-injection;
21 horses still met improvement criteria at day 90;
None of the 28 injected horses had adverse effects
The injection has been shown to be long lasting and can be given to horses anywhere from once every six months to once every 24 months.
Sounds like a miracle shot to keep horses comfortable throughout life, right?
Some veterinarians, such as Scollay, are still hesitant about pAAm and its manufacturers’ claims for use in racehorses.
“I have no qualms about using my retired gelding who has some arthritis and I just want him to be comfortable and enjoy whatever time he has left,” Scollay said.
But when it comes to using pAAm in the performance horse versus the racehorse, Scollay has reservations about its safety when used in the racing environment.
“The thing that worries me is when you read the promotional materials that are usually marketed to homeowners or non-professionals, it says ‘Indicated for use when the pain is isolated to a joint,’ so if the pain is from a joint, that’s suitable to use,” she explained. “There are a lot of things that can cause joint pain. Some of them are associated with or identified as precursors to potentially catastrophic injuries. Limping is a symptom. The underlying cause of lameness must be identified in order to develop an appropriate treatment plan. Failure to do so puts horses at unnecessary risk.”
“I am concerned that the safety work that has been done to date is not relevant enough to the racehorse. I’m not saying it’s unsafe, I’m saying we don’t know it’s safe for the horse population we manage. More information is needed.”
As of the publication date of this article, HISA regulations state that if pAAm is used in a horse’s joint, the horse cannot compete for 180 days. There will be a discussion on the use of joint injections at the December meeting of the International Federation of Horseracing Authorities’ Advisory Council on Banned Substances.
