Catastrophic fracture is one of the foremost concerns in the equine racing industry. The fracture of proximal sesamoid bones (PSBs) is the major cause of fatal racing injuries, accounting for 35.3% of fatalities in New York. Currently, no tests or imaging techniques are available to predict these fractures. To improve our understanding of the underlying causes of PSB fractures, our group assesses bone compositional properties in tissue retrieved at necropsy from a large population of racehorses with and without history of PSB fracture. Computed tomography (CT), dual x-ray absorptiometry (DXA) and Raman spectroscopy are being performed to investigate how the distribution of bone material properties will change as a function of various demographic parameters (e.g. age, sex, career duration). The bone mineral density (BMD) measurement will be compared to ash fraction, which is the gold standard for measuring BMD. This project is in collaboration with Prof. Reesink at the Cornell University College of Veterinary Medicine.

Key Findings The fracture group had a greater bone volume fraction compared to the non-fracture controls (Fig. XA), with regional differences in BV/TV corresponding to the most common fracture location in the basilar region (Fig. XB-C). These results suggest that altered mineral content or composition of organic matrix could be associated with catastrophic PSB fracture.

The bone volume fraction of the proximal sesamoid bone assessed by micro-CT scan was greater in the fracture group vs. non-fracture controls. (B-C) Bone volume fraction was greater in the fracture group than controls in all nine sub-regions. The most substantial increase in bone volume fraction occurred along the flexor and basilar surfaces (red regions on heat map). [Cresswell et al. 2018]

Future work: In next steps, MS student Leyi Chen is characterizing the material properties of the PSBs to understand regional differences in mineral and matrix properties. In addition, the study population will be extended from Thoroughbred racehorses to include non-racehorse controls. By combining information on exercise history, bone structure (micro-CT, DXA), and bone composition (Raman spectroscopy, ash fraction), our long-term goal is to develop a model to predict fracture risk in equine PSBs.

Heidi Reesink, Cornell University College of Veterinary Medicine