Effects of intra-articular corticosteroid administration on synovial biomarkers of inflammation, pain, and cartilage metabolism in young horses undergoing exercise

Abstract

Intra-articular corticosteroids (IAC) are administered to resolve joint inflammation; however, knowledge of the biological impacts of IAC in young, healthy horses is limited, and there are concerns that IAC are masking the root cause of pain and inflammation. Therefore, the objective was to determine the impacts of IAC administration on synovial fluid biomarkers of inflammation, pain, and cartilage metabolism. It was hypothesized that synovial inflammation, pain, and cartilage metabolism would decrease in response to IAC administration in young horses over a 56-d trial. Twenty-four Quarter Horses were stratified by age (825 ± 21 d), BW (409 ± 6 kg), and sex (12 mares, 12 geldings) and underwent a progressive workload (5 d/wk, 45 min/d) using a freestall exerciser. One radiocarpal joint was randomly assigned to one of 3 intra-articular treatments consisting of control (CON; n = 8), 6 mg (CORT6; n = 8), or 12 mg (CORT12; n = 8) of triamcinolone acetonide (TA). Synovial fluid was collected via arthrocentesis before IAC administration (d 0) and again on d 7, 14, 28, and 56 post-injection. Samples were analyzed for prostaglandin E₂ (PGE₂), substance P (SP), procollagen II c-propeptide (CPII), and collagen type II cleavage (C2C) by commercial ELISA. Data were analyzed using PROC MIXED of SAS, where non-normal data were log-transformed. The fixed effects were treatment, time, sex, and their interaction; however, sex was removed when nonsignificant. Significance was considered where P ≤ 0.05 and a trend where 0.05 < P ≤ 0.10. Mean synovial PGE₂ was 26% and 29% lower in CORT6 and CORT12 than in CON horses (P = 0.01), but did not differ between CORT6 and CORT12 (P = 0.75). There was a treatment × time interaction (P < 0.01) where CORT12 horses had 56% higher SP at d 7, and 52% higher SP at d 28 compared with CON (P = 0.02). Concentration of SP was 39% higher in CON horses compared with CORT6 on d 28 (P = 0.03), but TA dose did not differ (P = 0.12). On d 28, concentrations of SP were 54% higher in mares than geldings (P < 0.01). Both logCPII and logC2C peaked in CORT6 and CORT12 horses on d 7 (P < 0.01), but logCPII tended to remain higher until d 14 (P = 0.08). Similarly, net cartilage synthesis (logCPII:logC2C) was higher in CORT6 and CORT12 than CON on d 7 (P < 0.05) but returned to baseline by d 56. Therefore, intra-articular administration of TA reduced PGE₂, but net cartilage synthesis and SP increased regardless of TA dose. No differences between 6 or 12 mg of TA were observed, and further research is needed to establish a minimally effective dose.