Role of subchondral bone remodelling in collapse of the articular surface of Thoroughbred racehorses with palmar osteochondral disease.
Authors: Bani Hassan E, Mirams M, Ghasem-Zadeh A, Mackie E J, Whitton R C
Journal: Equine veterinary journal
Summary
# Palmar Osteochondral Disease: How Subchondral Bone Remodelling Drives Articular Surface Collapse Articular surface collapse represents a serious complication of palmar osteochondral disease in racing Thoroughbreds, yet the underlying mechanisms have remained poorly understood. Hassan and colleagues examined metacarpal bones from 36 racing Thoroughbreds using high-resolution computed tomography and electron microscopy to investigate whether altered bone remodelling—particularly in response to changes in training intensity—contributes to this collapse. Inward collapse of the calcified cartilage layer occurred in 21 horses and was strongly correlated with increased microfracture density in the calcified cartilage and superficial subchondral bone (rs = 0.62), whilst paradoxically, greater collapse was associated with lower porosity in deeper bone (6–10 mm). Critically, resting horses exhibited significantly higher porosity (median 14% versus 3.8%) and bone resorption activity in the superficial subchondral bone compared with those in active training, with some resting horses developing highly concentrated voids that appeared to undermine mechanical support for the overlying cartilage. These findings suggest that periods of reduced training intensity may accelerate focal subchondral resorption, ultimately leading to fatigue failure and cartilage collapse—a pattern that should prompt careful reconsideration of rehabilitation protocols and return-to-training timelines in horses recovering from palmar osteochondral lesions.
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Practical Takeaways
- •Maintenance of appropriate training intensity may help prevent subchondral bone resorption and subsequent articular collapse in racehorses—rest alone is counterproductive for bone support
- •Palmar osteochondral disease involves progressive fatigue failure initiated by microfractures in superficial bone layers; early detection of these changes via imaging may identify at-risk horses before collapse occurs
- •Management strategies should focus on optimizing training load and exercise intensity to maintain subchondral bone density and structure, rather than assuming rest is protective
Key Findings
- •Inward collapse of calcified cartilage was observed in 21 of 36 cases (58%) and was strongly associated with greater numbers of microfractures in calcified cartilage and superficial subchondral bone (rs = 0.62, P<0.001)
- •Deeper bone (6-10 mm) showed lower porosity with greater articular surface collapse (rs = -0.38, P = 0.023), suggesting differential remodelling patterns at depth
- •Resting horses had significantly higher porosity and eroded surface in superficial subchondral bone compared to training horses (median 14% vs 3.8%, P = 0.008), with some resting horses showing concentrated voids that compromised cartilage support
- •Articular surface collapse appears to be a sequel to fatigue injury of subchondral bone, potentiated by reduced-intensity exercise regimens