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Objectives— To compare monotonic biomechanical properties and fatigue life of a 5.5 mm broad limited-contact dynamic compression plate (5.5-LC-DCP) fixation with a 4.5 mm broad LC-DCP (4.5-LC-DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones.

Study Design— In vitro biomechanical testing of paired cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation.

Sample Population— Adult equine cadaveric MC3 bones (n=18 pair).

Methods— MC3 were divided into 3 test groups (6 pairs each) for: (1) 4-point bending single cycle to failure testing; (2) 4-point bending cyclic fatigue testing; and (3) torsional single cycle to failure testing. The 8-hole, 5.5 mm broad LC-DCP (5.5-LC-DCP) was applied to the dorsal surface of 1 randomly selected bone from each pair. One 8-hole, 4.5 mm broad LC-DCP (4.5-LC-DCP) was applied dorsally to the contralateral bone from each pair. Plates and screws were applied using standard ASIF techniques. All MC3 bones had mid-diaphyseal osteotomies. Mean test variable values for each method were compared using a paired t–test within each group. Significance was set at P<.05.

Results— Mean yield load, yield bending moment, composite rigidity, failure load and failure bending moment under 4-point bending, single cycle to failure, of the 5.5-LC-DCP fixation were significantly greater (P<.024) than those of the 4.5-LC-DCP fixation. Mean cycles to failure for 4-point bending was significantly (P<.05) greater for the 4.5-LC-DCP fixation compared with the 5.5-LC-DCP fixation. Mean yield load, mean composite rigidity, and mean failure load in torsion for the 5.5-LC-DCP fixation was not significantly different (P>.05) than those with the 4.5-LC-DCP fixation.

Conclusion— 5.5-LC-DCP fixation was superior to 4.5-LC-DCP fixation in resisting the static overload forces under palmarodorsal 4-point bending. There was no significant difference between 5.5-LC-DCP fixation and 4.5-LC-DCP fixation in resisting static overload forces under torsion; however, the 5.5-LC-DCP offers significantly less stability (80% of that of the 4.5-LC-DCP) in cyclic fatigue testing.

Clinical Relevance— The results of this in vitro study may provide information to aid in the selection of a biological plate for long bone fracture repair in horses.