ABSTRACT
BACKGROUND: Standard fatigue testing of bone uses a single load and frequency applied until failure. However, in situ, the subchondral bone of Thoroughbred racehorses is subjected to a combination (or a spectrum) of loads and frequencies during training and racing. OBJECTIVE: To investigate the use of a fatigue testing method for equine third metacarpal (McIII) subchondral bone under a spectrum of loading conditions which a racehorse is likely to experience during a fast workout. STUDY DESIGN: In vitro biomechanical experimental study. METHODS: McIII subchondral bone specimens (n = 12) of racehorses were harvested from left and right medial condyles. A novel fatigue loading protocol was developed based upon a standard sequence of gaits during a typical fast workout protocol. This loading pattern, or loading loop, was repeated until the failure of the specimen. RESULTS: The mean ± standard deviation for all specimens for total time-to-failure was 76,393 ± 64,243 s (equivalent to 18.3 ± 15.7 fast workouts). Ten of twelve specimens withstood at least one complete loop equivalent to a fast workout. All specimens failed during simulated gallop loading. MAIN LIMITATIONS: The resting time between loops was much shorter than in vivo resting time and specimens were unconfined during compressive testing. CONCLUSIONS: This novel fatigue loading protocol more closely mimics in vivo fatigue loading of McIII subchondral bone and demonstrates the importance of the highest speeds in the development of subchondral bone injury.
