Resident - Equine Surgery The Ohio State University Columbus, Ohio
The pathophysiological mechanisms responsible for superficial digital flexor tendon (SDFT) injuries in Thoroughbred racehorses are poorly understood. This research aims to determine if Thoroughbred SDFT fascicles and interfasicular matrix (IFM) characteristics undergo structure-function adaptations reflective of the horse’s age and race training. Mid-metacarpal SDFT (n=42 total) from 2-, 3-, 4- and 5-yo Thoroughbred racehorses necropsied through CAHFS were preserved within 48 hours of death/euthanasia. Longitudinal and transverse histological sections were imaged via Picro-Sirius Red (fascicle CSA) and confocal microscopy (concurrent elastin immunofluorescence and SHG-based collagen I structure) for quantifying fascicle CSA, IFM thickness and IFM elastin area fraction %. Biochemical total tendon elastin (FASTINTM) was quantified. Cyclical and load-to-failure tensile testing of whole tendons and fascicle/IFM units were conducted. Data were analyzed with one-way ANOVA and p<u><0.05. Fascicle CSA increased (p<0.01), whereas IFM elastin area fraction % and total elastin content decreased (p=0.041) with Thoroughbred racehorse age. Whole tendon biomechanical indices (yield stress-strain and elastic modulus) were not significantly different among age groups. Fascicle/IFM unit biomechanical analyses are ongoing. Accepting the study limitation of tendon degradation following death/euthanasia, total tendon and IFM elastin decreased with age, and reflects the low turnover of elastin relative to collagen; and serves as a plausible mechanism for SDFT cumulative biomechanical deficits and subsequent injury. These results emphasize the need to include fascicle/IFM architecture, and IFM elastin when delineating tendon adaptation and repair responses, and serve as a foundation for future research focusing on the impact of training schedules on racehorses’ susceptibility for SDFT injuries.
