Computed tomographic imaging of subchondral fatigue cracks in the distal end of the third metacarpal bone in the thoroughbred racehorse can predict crack micromotion in an ex-vivo model.
Authors: Dubois Marie-Soleil, Morello Samantha, Rayment Kelsey, Markel Mark D, Vanderby Ray, Kalscheur Vicki L, Hao Zhengling, McCabe Ronald P, Marquis Patricia, Muir Peter
Journal: PloS one
Summary
# Editorial Summary: CT-based prediction of subchondral fatigue crack progression in Thoroughbred MC3 bones Distal metacarpal condylar fractures remain a career-ending catastrophe in racing Thoroughbreds, yet no clinical tool currently exists to identify horses at greatest risk before catastrophic failure occurs. Dubois and colleagues developed an ex-vivo biomechanical model using cadaveric thoracic limbs from 40 racehorses with naturally occurring subchondral fatigue cracks, measuring crack dimensions on CT imaging before subjecting the metacarpal bones to compressive loading cycles that simulate high-speed galloping forces (–7,500N). The critical finding was a significant positive correlation between parasagittal crack area measured on CT reconstructions and the amount of micromotion that occurred within the crack during loading (Spearman's r = 0.32, p<0.05), with bones displaying crack areas exceeding 30 mm² showing substantially greater motion and therefore higher fracture propagation risk. Notably, crack dimensions in other planes (transverse and frontal) did not correlate with micromotion, suggesting that parasagittal crack geometry—the most common orientation in racing injuries—is specifically predictive of biomechanical instability. For clinical practice, this work provides a quantifiable CT threshold that could enable vets to identify high-risk horses during training or competition screening and make evidence-based decisions regarding racing soundness or targeted rehabilitation interventions, potentially preventing catastrophic injury.
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Practical Takeaways
- •CT imaging can now identify high-risk subchondral cracks in racing Thoroughbreds; cracks larger than 30 mm² in parasagittal area warrant serious consideration for retirement or reduced racing to prevent catastrophic fracture
- •This tool provides veterinarians with objective, quantifiable data to counsel owners on fracture risk and make evidence-based decisions about race fitness
- •Sagittal plane crack measurements on CT are the most clinically useful parameter; focus imaging and measurement in this plane for predicting fracture risk
Key Findings
- •Significant positive correlation found between CT-measured parasagittal crack area and crack micromotion under compressive loading (SR = 0.32, p < 0.05)
- •Subchondral cracks exceeding 30 mm² parasagittal crack area showed high risk of crack propagation and condylar fracture in the biomechanical model
- •CT imaging of crack dimensions in sagittal plane was predictive of micromotion, whereas transverse and frontal plane measurements were not significantly correlated
- •Histologic fatigue damage was not significantly correlated with CT-measured crack dimensions or extensometer micromotion