Use Caution When Injecting Joints in Metabolic Horses

Veterinarians report that laminitis may develop following routine joint injection with corticosteroid drugs in some horses. Elevated circulating insulin levels after injection may explain this increased risk of laminitis as “profound” elevations in insulin levels were observed in a recent study.^*

Specifically, horses with elevated resting insulin levels prior to injection were nine times more likely to reach insulin levels over 100 μU/mL, placing them at risk of developing laminitis. Due to these increased insulin levels following joint injections, experts suggest screening horses for underlying insulin dysregulation prior to performing joint injections with corticosteroids.

Joint injections are frequently performed in horses with inflammatory joint conditions, and corticosteroids such as triamcinolone acetate (TA) are commonly administered. While widely regarded as safe, there are reports of post-injection corticosteroid-induced laminitis in certain patients after only a single injection at reportedly “safe” doses.

“Risk factors for corticosteroid-induced laminitis are largely unknown; however, previous studies suggest that corticosteroids may induce metabolic derangements such as hyperglycemia and hyperinsulinemia. In turn, mounting evidence supports hyperinsulinemia as a driving force in endocrinopathic laminitis, which is also referred to as hyperinsulinemia-associated laminitis or HAL,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

To further explore the effect of a single joint injection of TA on insulin levels, 20 healthy horses were recruited from North Carolina State University’s teaching herd. Horses were sterilely administered 9 mg TA in each radiocarpal joint (upper knee joint) or 9 mg in each sacroiliac joint. The radiocarpal joint is a synovial joint, whereas the sacroiliac joint is not encapsulated and does not contain synovial (joint) fluid. Blood samples were collected from all horses at baseline before the injections and then intermittently up to 72 hours.

TA was absorbed systemically following both intrasynovial (knee) and extrasynovial (sacroiliac) injection. Peak absorption occurred eight hours after injection in both groups, and levels were higher following intrasynovial injection.

Insulin levels increased in both groups of horses after injection, and insulin levels were similar between the two groups.

“What the researchers also found was that baseline insulin levels were only considered normal, less than 20 μU/mL, in nine of the 20 apparently healthy horses. Insulin levels were higher after TA injection in the horses that had abnormally high baseline insulin levels at most time points up to 72 hours after injection,” Whitehouse said.

Horses with an elevated baseline insulin level had a peak insulin concentration of 197.5 μU/mL after TA injection, which was significantly higher than the peak insulin concentration of only 90μU/mL in horses with a normal baseline insulin level.

“Horses with high baseline insulin levels were nine times more likely to have insulin levels over 100 μU/mL post TA injection. Certain horses in this study achieved post-injection insulin levels that have been previously reported to cause or increase the risk of laminitis,” said Whitehouse.

In summary, this study identified a high number of apparently healthy horses with elevated resting insulin levels and found a profound and significant increase in insulin following a single injection of TA in either a synovial or extrasynovial injection. Based on these findings and the known risk of laminitis associated with such high levels of insulin, the researchers suggested that screening horses and ponies for insulin dysregulation may be “an important tool in reducing the risk of corticosteroid-associated laminitis.” According to the researchers, this agrees with the recommendations made by the Equine Endocrinology Group.

Controlling insulin levels in horses with insulin dysregulation is key to minimizing bouts of life-threatening laminitis. Once diagnosed, treatment should immediately be initiated, and the cornerstone to treatment is nutrition.

“Managing horses at an ideal body weight and body condition score is an important factor for both metabolic and joint health in horses. When selecting suitable forages and feeds for metabolic horses, consider calorie content, recommended feeding rates, and the amount of carbohydrates they provide,” advised Whitehouse.

Learn more about body condition scoring.

When metabolic horses are on a restricted diet, primarily forage, they may require a low-calorie vitamin/mineral supplement or ration balancer to ensure the diet is balanced, providing all the necessary micronutrients.

^*Hallowell, K.L., K. Dembek, C.R. Horne, H.K Knych, K.M. Messenger, and L.V. Schnabel. 2024. Systemic absorption of triamcinolone acetonide is increased from intrasynovial versus extrasynovial sites and induces hyperglycemia, hyperinsulinemia, and suppression of the hypothalamic-pituitary-adrenal axis. Frontiers in Veterinary Science 11:1388470.