One of the most common causes of lameness in horses is osteoarthritis (OA). Horse owners across the country spend countless hours and paychecks to try to supply effective pain management tools to their horses in hopes of providing comfort and prolonged happiness — whether in the pasture or in the show pen.
For years, the only known joint injection protocol with numerous studies to support claims for horses of all career check points (training, being competitive, retired) was hyaluronic acid. The hyaluronic acid (HA) injection is an intra-articular injection in the joint. It is popular with high-level competition horses, and is acceptable to use for racehorses.
“However, there is currently a model rule saying you cannot perform intra-articular injections in the 14 days prior to a race,” says Dr. Mary Scollay, chief of science for the Horseracing Integrity and Safety Authority's (HISA) Anti-Doping and Medication Control Program. “Not all of the states have adopted that, but it is the ARCI Model Rule.”
However, because of the expense of HA injections for purchase, there has been a push for animal science companies to produce a similar effect. Enter the nondegradable synthetic gel, polyacrylamide hydrogel.
Two of the more common types of injectable synthetic hydrogels are being marketed in the United States as Arthramid Vet and Noltrex Vet.
Noltrex Vet is a 4% polyacrylamide hydrogel (pAAm) that is being marketed to target “a root cause of joint pain by physically reducing friction.” According to the Noltrex Vet website, the manufacturer claims that the gel coats the cartilage of the horse's joint with a protective lubricating layer while reducing friction. The gel also forms a protective/lubricating layer on articulating surfaces and helps to restore and maintain a horse's healthy join function.
Arthramid Vet is a 2.5% cross-linked pAAm gel. According to Contura Vet's website, the manufacturer claims that the gel adheres to the synovial lining through the gel's ability to exchange water molecules. Then, the gel becomes integrated into the synovial lining 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 fully integrated into surrounding tissues, deeming it long-lasting.
Numerous studies have been shown that pAAm hydrogel has a lubricating ability that lowers the friction of cartilage, thus helping to promote a 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 team of researchers evaluated the pAAm hydrogel's effects on the tissue structure in six healthy horses' fetlock joints. They also tested the gel on 28 horses with naturally-occurring osteoarthritis.
The first six horses were found to have no adverse effects following the administration of the pAAm hydrogel and the hydrogel was still visible on the joint capsule lining when viewed at 28 and 56 days post-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 the criteria for improvement at Day 90;
None of the 28 horses with injections had any 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 injection to keep horses comfortable throughout their lives, right?
Some veterinarians, such as Scollay, are still hesitant about the claims of pAAm and its manufacturers as it pertains to use in racehorses.
“I have no qualms in using it on my retired gelding who has some arthritis and I just want him to be comfortable and enjoy whatever time he has left,” said Scollay.
But, when it comes to the use of pAAm in the performance horse versus the racehorse, Scollay has reservations about its safety when used in the racing environment.
“The thing that's troubling to me, is when you read the promotional materials that are typically promoted towards owners or laypersons, it reads 'Indicated for use when pain is isolated to a joint' so if the pain is coming from a joint, this is appropriate to use,” she explained. “There are lots of things that can cause joint pain. Some of them are associated or identified as precursors to potentially catastrophic injuries. Lameness is a symptom. The underlying cause of the lameness should be identified in order to develop an appropriate treatment plan. Failure to do so puts horses at unnecessary risk.”
“I'm concerned that the safety work that has been done to date is not that sufficiently relevant to the racehorse. I'm not saying it's unsafe, I'm saying we don't know that it is safe for the population of the horses we steward. More information is needed.”
As of the publishing date of this article, HISA regulations say that if pAAm is used in the horse's joint, the horse cannot race for 180 days. There will be a discussion on the topic of the use of joint injections at the December meeting of the International Federation of Horse Racing Authorities Advisory Council on Prohibited Substances.
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