Localisation and outcome of presumed thoracolumbar vertebral stress fracture in 35 UK Thoroughbred racehorses using nuclear scintigraphy.

BACKGROUND

Stress fracture is an important cause of mortality and morbidity in racing Thoroughbreds. Nuclear scintigraphy is the imaging modality of choice for investigating unlocalised stress-related bone remodelling in horses. Stress fractures of the caudal lumbar vertebral column have been previously described in both racing Quarter horses and racing Thoroughbreds post-mortem. There is a lack of literature describing the imaging appearance of vertebral stress fractures in racehorses ante-mortem.

OBJECTIVES

To describe: (1) ante-mortem scintigraphic appearance of presumed thoracolumbar vertebral stress fracture; (2) predilection sites of presumed thoracolumbar stress fracture and compare this to prior post-mortem descriptions; (3) if patient signalment had an association with presumed stress fracture; (4) the prognosis of return to racing post-diagnosis.

STUDY

DESIGN

Retrospective single-institutional case series.

METHODS

Thoroughbred racehorses undergoing nuclear scintigraphy during a 10-year period (2009-2019). Images reviewed by two assessors for abnormal increased radiopharmaceutical uptake in the thoracolumbar vertebral column consistent with presumed stress fracture; inclusion by consensus. Chi-square test performed to investigate outcome.

RESULTS

Thirty-five racing Thoroughbreds included and 41 presumed stress fractures identified. The caudal lumbar vertebral column was the most common site of presumed thoracolumbar vertebral stress fracture, consistent with previously reported post-mortem findings. The thoracolumbar junction was identified as the second most common site of presumed stress fracture. A positive outcome, defined as return to racing, was present in 65.9% of horses; 95% CI (51.4%, 80.4%). Patient sex was the only factor associated with outcome, with female patients having a lower likelihood of returning to racing.

MAIN LIMITATIONS: Retrospective observational nature with only a small sample size.

CONCLUSIONS

The caudal lumbar vertebral column was the most common site of presumed thoracolumbar vertebral stress fracture, followed by the thoracolumbar junction. Lamina/articular process was the most common sublocation. Most horses had a positive outcome. Female sex was the only factor significantly associated with a worse outcome.