Biomechanical and Microstructural Properties of Subchondral Bone From Three Metacarpophalangeal Joint Sites in Thoroughbred Racehorses.
Authors: Pearce Duncan J, Hitchens Peta L, Malekipour Fatemeh, Ayodele Babatunde, Lee Peter Vee Sin, Whitton R Chris
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Subchondral bone fatigue injury remains a significant cause of career-ending lameness in racehorses, yet the mechanical behaviour of this tissue varies substantially across different weight-bearing sites within the fetlock joint. Duncan Pearce and colleagues examined cartilage-bone specimens from three distinct locations—the dorsal and palmar third metacarpal condyles and proximal sesamoid bone—comparing superficial (0–2 mm) and deeper (2–4 mm) subchondral layers using micro-computed tomography, cyclic compression testing, and quantification of accumulated microdamage. The dorsal metacarpal condyle demonstrated notably lower bone volume fraction, mineral density, and stiffness than both the palmar condyle and sesamoid bone, whilst superficial layers across all sites proved consistently more compliant than deeper bone despite variable changes in density and microdamage—a finding that challenges the assumption that mechanical properties simply reflect structural composition. During cyclic loading, superficial bone dissipated greater energy (particularly at palmar and sesamoid sites), suggesting this compliant zone functions as a shock-absorbing interface, though whether this represents an adaptive response or pathological microdamage accumulation remains uncertain. For practitioners involved in injury prevention and management, these results highlight that subchondral properties are site-specific and depth-dependent, implying that loading tolerance and injury risk likely differ across the fetlock joint, with potential implications for understanding why dorsal metacarpal disease predominates in racing Thoroughbreds and how training intensity and surface modifications might differentially affect distinct anatomical regions.
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Practical Takeaways
- •The dorsal (top) surface of the fetlock joint is biomechanically weaker and may be more vulnerable to fatigue injury in racehorses—consider this when assessing load distribution in racing athletes
- •The superficial bone layer functions as an energy-absorbing 'shock absorber' particularly at common injury sites (palmar condyle, sesamoid); protective strategies should aim to preserve this compliant layer
- •Progressive stiffening of subchondral bone during cyclic loading may indicate adaptation or early microdamage accumulation; monitoring changes in fetlock mechanics during training could help detect at-risk horses early
Key Findings
- •Dorsal metacarpal condyle subchondral bone is structurally weaker (lower bone volume fraction, mineral density, and stiffness) compared to palmar condyle and proximal sesamoid bone
- •Superficial subchondral bone is less stiff than deep bone at all sites, but this difference is smallest at the dorsal condyle
- •Superficial bone dissipates more energy (greater hysteresis) at palmar and sesamoid sites, suggesting a specialized role in shock absorption
- •Bone stiffness increased with cyclic loading while hysteresis decreased across all sites, indicating progressive mechanical adaptation or microdamage effects