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Comparison of macrostructural and microstructural bone features in Thoroughbred racehorses with and without midbody fracture of the proximal sesamoid bone

Lucy A. Anthenill DVM, PhD1, Ian A. Gardner BVSc, PhD2, Roy R. Pool DVM, PhD3, Tanya C. Garcia MS4, and Susan M. Stover DVM, PhD5
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  • 1 J.D. Wheat Veterinary Orthopedic Research Laboratory, Departments of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616
  • | 2 Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616
  • | 3 Department of Veterinary Pathology, College of Veterinary Medicine and Biological Sciences, Texas A&M University, College Station, TX 77843.
  • | 4 J.D. Wheat Veterinary Orthopedic Research Laboratory, Departments of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616
  • | 5 J.D. Wheat Veterinary Orthopedic Research Laboratory, Departments of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616

Abstract

Objective—To compare macrostructural and microstructural features of proximal sesamoid bones (PSBs) from horses with and without PSB midbody fracture to gain insight into the pathogenesis of PSB fracture.

Sample Population—PSBs from 16 Thoroughbred racehorses (8 with and 8 without a PSB midbody fracture).

Procedures—Parasagittal sections of fractured and contralateral intact PSBs from horses with a PSB fracture and an intact PSB from age- and sex-matched control horses without a PSB fracture were evaluated for visual, radiographic, microradiographic, histologic, and his-tomorphometric differences in bone porosity, vascular channels, heme pigment, trabecular anisotropy, and pathological findings.

Results—Fractured PSBs and their contralateral intact PSBs had more compacted trabecular bone than did control PSBs. Focal repair or remodeling was evident in the palmar aspect of many fractured and contralateral intact PSBs. Fracture coincided with microstructural features and propagated from the flexor to the articular surface.

Conclusions and Clinical Relevance—Fractured PSBs had adapted to high loading but had focal evidence of excessive remodeling and porosity that likely predisposed the horses to complete fracture and catastrophic injury. Detection of focal injury before complete fracture provides an opportunity for prevention of catastrophic injury. Development of diagnostic imaging methods to assess porosity of PSBs may help to identify at-risk horses and allow for modifications of training and racing schedules to reduce the incidence of PSB fracture in Thoroughbred racehorses.

Contributor Notes

Supported by the Grayson Jockey Club Research Foundation Incorporated and the Center for Equine Health, with funds provided by the State of California parIMutuel fund and contributions by private donors.

Address correspondence to Dr. Stover (smstover@ucdavis.edu).