Resumen de Quantitative comparison of bone mineral density characteristics of the distal epiphysis of third metacarpal bones from Thoroughbred racehorses with or without condylar fracture

Sophie H. Bogers, Chris W. Rogers, Charlotte Bolwell, Wendi Roe, Erica Gee, C. Wayne McLlwraith

• Quantitative comparison of bone mineral density characteristics of the distal epiphysis of third metacarpal bones from Thoroughbred racehorses with or without condylar fracture Sophie H. Bogers, BVSC, MVSC; Chris W. Rogers, PhD; Charlotte Bolwell, PhD; Wendi Roe, BVSC, PhD; Erica Gee, BVSC, PhD; C. Wayne McIlwraith, BVSC, PhD, DSC Marion DuPont Scott Equine Medical Centre, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 20176. (Bogers); Massey Equine Institute of Veterinary, Animal and Biomedical Sciences, College of Sciences, Massey University, Palmerston North 4442, New Zealand. (Rogers, Bolwell, Gee); Department of Pathobiology, Institute of Veterinary, Animal and Biomedical Sciences, College of Sciences, Massey University, Palmerston North 4442, New Zealand. (Roe); Orthopedic Research Center, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523. (McIlwraith) Address correspondence to Dr. Rogers (c.w.rogers@massey.ac.nz) OBJECTIVE To compare regional proportions and spatial distributions of volumetric bone mineral density (BMDv) of the palmar aspect of the distal epiphysis of the third metacarpal bone (McIII) in limbs with or without a condylar fracture from Thoroughbred racehorses.

  SAMPLE McIIIs from cadavers of Thoroughbred racehorses with (n = 6 bones) and without (8) a condylar fracture.

  PROCEDURES BMDv and spatial distributions of BMDv in peripheral quantitative CT images of the distal epiphysis of McIIIs were quantitatively assessed with spatial analysis software. Relative proportions of voxels within 9 threshold categories of BMDv and spatial statistics for BMDv distribution were compared between fractured and nonfractured limbs.

  RESULTS No significant differences in BMDv characteristics were identified between fractured and nonfractured limbs, although fractured limbs had a lower proportion of voxels in the BMDv thresholds 700 to < 800 mg/cm3 and 800 to < 900 mg/cm3 but a higher proportion of voxels in the BMDv threshold 1,000 to < 1,100 mg/cm3 for the central condylar region of the medial condyle. Results of spatial analysis reflected the response of bone to race training rather than differences between fractured and nonfractured limbs. In both limb groups, uniform clusters of low BMDv with areas of high BMDv were identified.

  CONCLUSIONS AND CLINICAL RELEVANCE BMDv characteristics of the distal epiphysis of McIII reflected training load, and fracture characteristics were subtle. Serial imaging techniques in conjunction with detailed training data are required to elucidate the onset of the pathological response to load in horses.