Screw fixation in lag fashion of equine cadaveric metacarpal and metatarsal condylar bone specimens: a biomechanical comparison of shaft and cortex screws.

Summary

# Editorial Summary Condylar fractures of the equine third metacarpal and metatarsal bones present a significant clinical challenge, and the biomechanical properties of fixation methods directly influence healing outcomes and load tolerance. Rahm and colleagues subjected cadaveric condylar bone specimens to lag screw fixation using different cortex screw designs (4.5 and 5.5 mm diameter, with shafts of 0, 20, or 25 mm length), then measured insertion torque, stiffness, yield strength, and displacement under shear loading. Screws incorporating a shaft demonstrated substantially superior performance: they were 30–40% stiffer, 60–70% stronger, and reduced displacement by 55–60% compared with shaftless designs, with longer shafts performing better than shorter ones; notably, screws with shafts tolerated 80–95 kg additional load before yielding, whilst insertion effort differences between designs were clinically negligible. These findings suggest that cortex screws with a long shaft (25 mm) in 4.5 or 5.5 mm diameter represent the biomechanically optimal choice for lag fixation of equine metacarpal and metatarsal condylar fractures, offering improved stability without requiring disproportionate surgical effort or insertion force.

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Key Findings

• •Cortex screws with shaft were 30-40% stiffer and 60-70% stronger than screws without shaft
• •Shafted screws tolerated 80-95 kg more force before yielding compared to non-shafted screws
• •At 3 kN load, displacement with shafted screws was 55-60% of non-shafted screws
• •Long shaft screws performed better than short shaft screws with minimal difference in insertion effort

Conditions Studied