Catastrophic failure of the proximal sesamoid bones (PSBs) in elite racehorses results in dramatic, often fatal, fractures that occur during high speed races. PSB fractures often occur without prior symptoms in otherwise healthy, athletic animals. Fracture pathology is poorly understood, and it is therefore unclear what aspects of bone structure and material properties contribute to fracture risk. Understanding changes in bone morphometry (i.e., shape, density, volume) that increase fracture risk could lead to screening techniques to identify horses at increased risk of fracture. The aims of the proposed research are to identify quantitative computed tomographic (CT) imaging parameters associated with catastrophic PSB fracture in Thoroughbred racehorses and to directly compare the ability of quantitative microCT and quantitative standard CT to detect differences in PSBs from horses with and without fracture. PSB fractures account for the majority of fatal musculoskeletal injuries on U.S. racetracks. Although other researchers have identified changes such as increased overall bone mineral density in horses with catastrophic PSB fracture, there are currently no clinically relevant screening modalities to detect these changes before they occur. As such, there is a critical unmet need to translate research findings into a clinically applicable method to identify subtle changes in PSBs that may be indicative of bone pathology and fracture risk in order to enhance racehorse welfare and to salvage public perception of the integrity of racing. By combining epidemiologic factors such as age, sex, and exercise history with quantitative CT (QCT) imaging parameters, our goal is to generate fracture risk prediction tools that will be able to help racehorse veterinarians, owners and trainers make informed decisions about the suitability of horses to race. Our long-term goals are to improve equine welfare, to mitigate negative publicity associated with horseracing, and to enhance our understanding of how equine bone adapts to exercise. We hypothesize that equine PSBs undergo prodromal changes in shape, density and material properties prior to catastrophic fracture in Thoroughbred racehorses, and that quantitative CT is an efficient and effective method for evaluating fracture risk in racehorses.