An in vitro biomechanical comparison of a 5.5 mm locking compression plate fixation with a 4.5 mm locking compression plate fixation of osteotomized equine third metacarpal bones.
Authors: Sod Gary A, Riggs Laura M, Mitchell Colin F, Martin George S, Gill Marjorie S
Journal: Veterinary surgery : VS
Summary
# Editorial Summary Selecting appropriate plate fixation for equine third metacarpal fractures requires evidence-based decision-making, yet limited biomechanical data directly compare commonly used implant systems. Sod and colleagues conducted an in vitro comparison of 5.5-mm and 4.5-mm locking compression plates (LCP) applied to osteotomized cadaveric equine MC3 bones, testing both single-cycle failure under bending and torsional loads, as well as cyclic fatigue resistance under repetitive bending forces. The 5.5-mm plate demonstrated significantly superior performance across all mechanical parameters: it withstood approximately 31% more bending cycles before failure (170,535 versus 129,629 cycles), and under torsional loading showed markedly greater yield load (151.4 versus 97.6 Nm) and composite rigidity (790.3 versus 412.3 Nm/rad). For equine practitioners managing high-demand athletic animals or cases where early return to function is prioritised, these findings support selection of the broader 5.5-mm plate construct when fracture configuration and anatomical considerations permit, as the improved fatigue resistance may reduce the risk of fixation failure during the healing period.
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Practical Takeaways
- •The 5.5 mm LCP offers superior biomechanical properties for equine third metacarpal fractures, particularly when fatigue loading is expected during rehabilitation
- •If selection between these two plate sizes is necessary, the 5.5 mm plate provides greater safety margins against both catastrophic failure and fatigue crack initiation
- •Consider using 5.5 mm LCP for high-demand horses or fractures in horses requiring early return to work; 4.5 mm may be adequate for lower-demand situations
Key Findings
- •5.5 mm LCP demonstrated significantly greater yield load, failure load, and bending moment compared to 4.5 mm LCP under 4-point bending testing
- •5.5 mm LCP showed 31% higher cycles to failure (170,535 vs 129,629 cycles) under cyclic fatigue bending
- •5.5 mm LCP had superior torsional strength with 55% higher yield load (151.4 vs 97.6 Nm) and 91% higher composite rigidity (790.3 vs 412.3 Nm/rad)
- •Broader plate design provides mechanical advantage in resisting both static overload and cyclic fatigue forces in equine MC3 fracture fixation