Characterizing Compositional and Mechanical Changes of Equine Proximal Sesamoid Bone Associated with Catastrophic Race Failure

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Catastrophic breakdown injuries are a major and serious problem in Thoroughbred racing. The published overall Thoroughbred breakdown injury rate from the Equine Injury Database for the 2016 racing season is 1.54 per 1,000 starts (, down from a range of 1.88 �] 2.00 in the years 2009 �] 2014. Continuing the encouraging progress from the last two years will be facilitated by further investigations of the nature and development of skeletal lesions that predispose to catastrophic injury . new knowledge that will be important both for Thoroughbreds and other racing breeds as well. Proximal sesamoid fractures are one of the most commonly reported fatal catastrophic injuries in North American Thoroughbred racing. The medial and lateral proximal sesamoid bones (PSB) are a component of the suspensory apparatus and located on the palmar/plantar surface of the metacarpophalangeal (fetlock) joint. The suspensory apparatus functions as an energy absorbing and storing structure that limits hyperextension of the fetlock joint during high�]speed locomotion. The PSBs act as a critical lever for this mechanism. Investigation of fracture mechanics (in human and animal models) have led to parameters such as bone mineral density changes as risk factors, however no single bone parameter has been demonstrated to be a pathognomonic �gsilver bullet�h in predicting bone fatigue and fracture potential. Therefore, an approach of looking at overall bone quality, which encompasses both structural and material properties, provides a more complete assessment of the tissue. A critical knowledge gap in understanding catastrophic injuries relates to the interaction of bone matrix components and mechanical robustness in response to high�]speed exercise and bone fatigue. Previous work has determined catastrophic injuries are often the result of cumulative fatigue of the skeletal tissues and ultimate structural failure rather than a single supraphysiological stress event (i.e., �gbad step�h). Changes to bone over time related to cyclic loading of the limb can lead to impaired biomechanical properties. While much work has focused on other types of catastrophic injures (i.e. lateral condylar fractures), the literature is more limited for PSB fractures despite their epidemiological significance. The current project will address this knowledge gap through a multidimensional approach to assess overall bone quality of the PSB in the context of identifying factors that may predispose to failure. We propose to compare bone quality parameters of the PSBs in 1) horses that have not entered work, 2) horses in training/racing euthanized for non�]skeletal issues and 3) horses in training/racing that have sustained a proximal sesamoid bone fracture. For microstructural analysis, Fourier Transform InfraRed (FTIR) analysis and histomorphometry will provide a new and potentially important platform to assess mineralized and non�]mineralized components of PSBs. The molecular structure of these mineralized and non�]mineralized components and their response to exercise may be critical factors in the ability of PSBs to withstand fatigue injury. To characterize the mechanical properties of bone from these study groups, macro (three point bending and Brazilian compressive analyses) and micro level (Reference Point Indentation) mechanical experiments will be performed to evaluate bone stiffness, strength and toughness. The proposed methods will be performed on the same set of bones thereby allowing a comprehensive bone quality assessment and comparison between experimental groups. The integration of the proposed bone quality methods provides an exciting opportunity to evaluate compositional and biomechanical properties of the proximal sesamoid bones and their role in suspensory apparatus failure. These proposed experiments will provide insight on the genesis of these fractures and baseline data for additional research, which is critical to the health and welfare of both horses and jockeys in the racing industry.
Effective start/end date3/1/192/28/20


  • KY Horse Racing Commission: $50,000.00


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