Comparison of planar digital radiography and helical standing computed tomography for assessment of condylar stress fracture risk in Thoroughbred racehorses

Background: Catastrophic injury has a low incidence but leads to the death
of many Thoroughbred racehorses. Objectives: To determine sensitivity,
specificity, and reliability for condylar stress fracture risk assessment
from fetlock digital radiographs (DR) and standing computed tomography
(sCT). Study design: Controlled ex vivo experiment. Methods: A blinded set
of thoracic limb fetlock DR and sCT images were prepared from 31
Thoroughbreds. Four observers evaluated the condyles and parasagittal
grooves (PSG) of the third metacarpal bone for the extent of dense bone
and lucency/fissure and assigned a risk assessment grade for condylar
stress fracture. Sensitivity and specificity for detection of subchondral
structural changes in the condyles and PSG and for risk assessment for
condylar stress fracture were determined by comparison with a reference.
Agreement between observers and the reference assessment and reliability
between observers were determined. Intra-observer repeatability was also
assessed. Results: Sensitivity for detection of structural change was
lower than specificity for both imaging methods and all observers. For
horses with normal risk, observer assessment often agreed with the
reference. Sensitivity for risk assessment was lower than specificity for
all observers. For horses with a high risk of injury, observers generally
underestimated risk. Diagnostic sensitivity of risk assessment was
improved with sCT imaging, particularly for horses with elevated risk of
injury. Assessment repeatability and reliability was better with sCT than
DR. Main limitations: The ex vivo study design influenced DR image sets.
Conclusions: Risk assessment through screening with diagnostic imaging is
a promising approach to improve injury prevention in racing Thoroughbreds.
Knowledge of sensitivity and specificity of fetlock lesion detection
provides the critical guidance needed to improve screening programs for
racehorses. We found improved detection of MC3 subchondral structural
change and risk assessment for condylar stress fracture with sCT ex vivo.