Joint inflammation and osteoarthritis (OA) are common in athletic horses, frequently resulting in lameness, poor performance, and economic losses. Veterinarians can provide symptomatic relief from joint discomfort caused by OA via intra-articular injections using a variety of medications. Examples include corticosteroids (e.g., triamcinolone acetate, methylprednisolone acetate), hyaluronic acid, polysulfated glycosaminoglyans, and various biologic therapies, such as stem cells, platelet-rich plasma (PRP), autologous conditioned serum (ACS, interleukin-1 receptor antagonist protein, IRAP), and autologous protein solution.
Which medication(s) veterinarians inject into which joint and how frequently that joint can be medicated are factors ultimately determined by the veterinarian using their own clinical experience. These choices therefore rely heavily on anecdotal evidence rather than scientific guidelines. In other words, there are no hard and fast rules regarding joint injections due to the lack of head-to-head comparisons of the various treatment options.
To gain a deeper understanding of how veterinarians are injecting joints, a survey sanctioned by the American Association of Equine Practitioners (AAEP) was conducted in 2019. Those data were subsequently analyzed by Dr. Gustavo Zanotto from the department of large animal clinical sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University. Dr. David Frisbie from the department of clinical sciences, Collage of Veterinary Medicine and Biological Sciences, Colorado State University was co-author of the study.
Zanotto recently presented data garnered from that 2019 survey at the 2021 AAEP Annual Convention held in Nashville, TN.
In total, 407 equine practitioners participated in the survey, the majority of which worked with racehorses (Thoroughbreds, Quarter Horses) and Warmbloods. Those veterinarians had extensive (>20 years) of clinical experience from which to draw their survey answers from.
Here are some of the most important take-away points garnered from the survey applicable to Thoroughbred racehorses.
Frequency of Injection
Approximately two-thirds of veterinarians were concerned about treating joints too frequently with corticosteroids for fear of causing harm, presumably to the articular cartilage.
“About 75% of responding veterinarians said that they believed joints can be damaged by treating too frequently. Most believe you can inject a joint once only every six months, whereas 30% of practitioners say you can do it every three months,” said Zanotto.
Despite these beliefs/recommendations suggested by practitioners on the survey, Zanotto says, “There is no strong scientific evidence regarding minimum frequency of joint injections.”
Steroid Selection
Triamcinolone and methylprednisolone are used most often in high- and low-motion joints by equine veterinarians, respectively. Nonetheless, almost three-quarters of practitioners still feel that triamcinolone is either somewhat likely or very likely to contribute to laminitis. As a result, survey respondents reported using limited amounts of triamcinolone, both in a single joint and as a total dose per horse. Based on the survey, most practitioners reported using 5-10 mg triamcinolone in a single joint and 20-40 mg of methylprednisolone. Most practitioners use less than 40 mg of triamcinolone per horse, and about 50% used no more than 18 mg triamcinolone per horse.
Based on scientific evidence, however, Zanotto said, “Triamcinolone does not appear to increase the risk of laminitis in healthy horses, and a safe total body dose has not yet been established.”
Antibiotic (Ab)use
In this survey, 55.6% of veterinarians admitted to always using an antibiotic such as amikacin when injecting medication into a joint. Perhaps more disquieting was the fact that the number of veterinarians using an antibiotic when medicating a joint actually increased from a similar survey in conducted back in 2009.
“This increased use of antibiotics is an alarming finding because there is evidence that amikacin is toxic to cartilage cells, as well as increased concern regarding antibiotic resistance,” explained Zanotto.
Reasons that veterinarians cited for using antibiotics intra-articularly were poor environmental conditions and “coincident corticosteroid injections.”
Such statements should give us pause for two main reasons. First, Zanotto pointed out that no evidence actually exists supporting the notion that joints medicated with corticosteroids are at an increased risk of infection.
Second, there is no evidence that the environmental conditions in which most equine practitioners inject joints contributes to joint infections. In fact, according to Dr. Lynn Pezzanite from Colorado State University, joint infections are exceedingly rare.
During her presentation at the 2021 AAEP Annual Convention, Pezzanite relayed data she retrospectively collected from joint injections performed between 2014 and 2018. In total, 3,866 synovial injections were performed on 1112 horses over 1623 sessions. Of those, 643 sessions were performed in the field.
Pezzanite's data revealed that the risk of sepsis (infection) was similar between joints injected in the field and hospital and between joints that had or had not been treated with an antibiotic. Overall, the frequency of sepsis was 1 in 967 injections, or about 0.1%.
Biologic Therapies Gaining a Foothold
Perhaps due to equine practitioners' ever-increasing familiarity with the various commercially available biologic therapies available as well as the perceived benefits of such therapies, their use is increasing. According to the survey, IRAP is the most popular biologic therapy, followed by PRP, autologous protein solution, stem cells, then bone marrow aspirate/concentrate. Cost is a major determinant of which biologic is ultimately used.
In sum, despite how frequently joint injections are being performed there is still a profound lack of evidence-based guidance regarding frequency of injection and recommended doses, particularly for corticosteroids. One of the more alarming findings, however, is the rampant and unnecessary overuse of antibiotics in routine joint injections for prophylactic purposes.
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