Proton magnetic resonance spectroscopy of the distal metacarpus or metatarsus in thoroughbred racehorses with and without catastrophic fractures.

Introduction / Purpose: Fractures of the third metacarpal/metatarsal bone are common in racehorses. The aim of this study was to quantify the 1H spectra for the equine metacarpal/metatarsal bone and compare the fat content to bone mineral density (BMD) in racehorses with and without fractures. Methods: Cadaver limbs from Thoroughbred racehorses in training were recruited. Each limb underwent magnetic resonance imaging at 3T using a knee coil followed by single voxel magnetic resonance spectroscopy at 3 locations (lateral condyle, medial condyle, centre of the distal diaphysis of the third metacarpal/metatarsal bone). Percentage fat content (FC) was calculated at each location. Each limb underwent computed tomography using a helical 64-slice CT scanner and mean BMD was calculated at the same 3 locations. All images were subjectively graded for sclerosis on MRI and CT. Results: A statistically significant negative correlation was identified for mean BMD and percentage FC for all condyles and in the proximal bone marrow (correlation coefficient =-0.36; p=0.040). The median percentage FC in the bone marrow of the distal diaphysis was lower in horses with fractures (88%) compared to controls (91%)(p=0.02). Median BMD was significantly higher (p=0.0009 for MRI; p=0.0018 for CT) and FC was significantly lower (p=0.0003 for MRI and p=0.0012 for CT) in condyles with a higher sclerosis grade on MRI and CT. Discussion / Conclusion: Fat content decreases with an increase in BMD in trained racehorses. These findings suggest that fat and bone may be capable of mutual regulation in Thoroughbred racehorses.