Subchondral focal osteopenia associated with proximal sesamoid bone fracture

If this pans out careful radiology or at the least MRI may be able to find those with the subchondral weakness and therefore susceptible to sesamoid fracture prior to the catastrophe and allow treatment and prevention.
DrO

Equine Vet J. 2020 May 31.
Subchondral focal osteopenia associated with proximal sesamoid bone fracture in Thoroughbred racehorses.
Shaffer SK1, To C2, Garcia TC2, Fyhrie D3, Uzal FA4, Stover SM2.

Author information:
1. Department of Mechanical and Aerospace Engineering, University of California-Davis, Davis, California, USA.
2. Department of Surgical and Radiological Sciences, University of California-Davis, Davis, California, USA.
3. Departments of Orthopedic Surgery and Biomedical Engineering, University of California-Davis, Davis, California, USA.
4. California Animal Health and Food Safety Laboratory System, University of California-Davis, Davis, California, USA.
Abstract

BACKGROUND:
Proximal sesamoid bone (PSB) fracture is the most common fatal injury in Thoroughbred (TB) racehorses in the United States. Epidemiological and pathological evidence indicate PSB fracture is likely the acute culmination of a chronic stress-related process. However, the etiopathogenesis of PSB fracture is poorly understood.
OBJECTIVE:

To characterize bone abnormalities that precede PSB fracture.

STUDY DESIGN:
Two retrospective case-control groups of PSBs from TB racehorses with, and without, unilateral biaxial PSB fracture.

METHODS:
Proximal sesamoid bones were harvested postmortem from TB racehorses euthanized for unilateral biaxial PSB fracture (cases) or causes unrelated to PSB fracture (controls) while racing or training. The fractured medial PSB (FX-PSB) and contralateral intact medial PSB (CLI-PSB) from racehorses that sustained PSB fracture, and an intact medial PSB (CTRL-PSB) from racehorses that did not have a PSB fracture were collected as case and control specimens. Study 1) distributions of morphologic features were compared among case and control groups using visual examination, photographs, radiographs, and histology of whole PSBs and serial sagittal sections (10 FX-PSB, 10 CLI-PSB, 10 CTRL-PSB). Study 2) local bone volume fraction and mineral densities were compared among case and control PSBs using microcomputed tomography (9 FX-PSB, 9 CLI-PSB, 9 CTRL-PSB).

RESULTS:
A focal subchondral lesion characterised by co-localised focal discoloration, radiolucency, osteopenia, low tissue mineral density, and a surrounding region of dense cancellous bone was identified in most case horses but not in controls. This subchondral lesion was found in a slightly abaxial mid-body location and was bilaterally present in most case horses.

MAIN LIMITATIONS:
The postmortem samples may not represent the spectrum of abnormalities that occur throughout the development of the subchondral lesion. Lateral PSBs were not examined, so their contribution to biaxial PSB fracture pathogenesis is unknown.

CONCLUSION:
Abaxial subchondral lesions are consistent with pre-existing injury and likely associated with PSB fracture.