In vitro biomechanical comparison of a modified 5.5 mm locking compression plate fixation with a 5.5 mm locking compression plate fixation of osteotomized equine third metacarpal bones

OBJECTIVES: To compare number of cycles to failure for palmarodorsal 4-point bending of a modified 5.5 mm broad locking compression plate (M5.5-LCP) fixation with a 5.5 mm broad LCP (5.5-LCP) fixation used to repair osteotomized equine third metacarpal (MC3) bones. STUDY DESIGN: In vitro biomechanical testing. ANIMAL POPULATION: Adult equine cadaveric MC3 bones (n=6 pairs). METHODS: An 8-hole, M5.5-LCP, obtained by having a 1.0 mm thickness removed from the bone contact portion of the 5.5-LCP, was applied to the dorsal surface of 1 randomly selected MC3 from each pair, and an 8-hole, 5.5-LCP was applied dorsally to the contralateral bone from each pair using a combination of cortical and locking screws. Plates and screws were applied using standard ASIF techniques to MC3 bones with a mid-diaphyseal osteotomy. MC3 constructs had palmarodorsal 4-point bending cyclic fatigue testing. Mean cycles to failure for each method were compared using a paired t-test within each group. Significance was set at P\u3c.05. RESULTS: Mean±SD cycles to failure of the M5.5-LCP fixation (188,641±17,971) was significantly greater than that of the 5.5-LCP fixation (166,497±15,539). CONCLUSION: M5.5-LCP fixation was superior to 5.5-LCP fixation of osteotomized equine MC3 bones in resisting cyclic fatigue under palmarodorsal 4-point bending. CLINICAL RELEVANCE: This suggests that biological plate fixation is not the ideal choice for osteotomized equine MC3 bones