An in vitro biomechanical comparison of an interlocking nail system and dynamic compression plate fixation of ostectomized equine third metacarpal bones

Objective-To compare the mechanical properties of two stabilization methods for ostectomized equine third metacarpi (MC3): (1) an interlocking nail sy stem and (2) mio dynamic compression plates. Animal or Sample Population-Ten pairs of adult equine forelimbs intact from the midradius distally. Methods-Ten pairs of equine MC3 were divided into two test groups (five pai rs each): caudocranial four-point bending and torsion. Interlocking nails ( 6 hole, 13-mm diameter, 230-mm length) were placed in one randomly selected bone from each pair. Two dynamic compression plates one dorsally (12 hole, 4.5-mm broad) and one laterally (10 hole, 4.5-mm broad) were attached to t he contralateral bone from each pair. All bones had 1 cm mid-diaphyseal ost ectomies. Five construct pairs were tested in caudocranial four-point bending to dete rmine stiffness and failure properties. The remaining five construct pairs were tested in torsion to determine torsional stiffness and yield load. Mea n values for each fixation method were compared using a paired t-test withi n each group. Significance was set at P < .05. Results-Mean (+/-SEM) values for the MC3-interlocking nail composite and th e MC3-double plate composite, respectively, in four-point bending were: com posite rigidity, 3,454 +/- 407.6 Nm/rad and 3,831 +/- 436.5 Nm/rad; yield b ending moment, 276.4 +/- 40.17 Nm and 433.75 +/- 83.99 Nm. failure bending moment, 526.3 +/- 105.9 Nm and 636.2 +/- 27.77 Nm. There was no significant difference in the biomechanical values for bending between the two fixatio n methods. in torsion, mean (+/-SEM) values for the MC3-interlocking nail c omposite and the MC3-double plate composite were: composite rigidity, 124.1 +/- 16.61 Nm/rad and 262.4 +/- 30.51 Nm/rad; gap stiffness, 222.3 +/- 47.3 2 Nm/rad and 1,557 +/- 320.9 Nm/rad; yield load, 94.77 +/- 7.822 Nm and 130 .66 +/- 20.27 Nm, respectively. Composite rigidity, Sap stiffness, and yiel d load for double plate fixation were significantly higher compared with in terlocking nail fixation in torsion. Conclusions-No significant differences in biomechanical properties were ide ntified between an interlocking nail and double plating techniques for stab lilization of ostectomized equine MC3 in caudocranial four-point bending. D ouble plating fixation was superior to interlocking nail fixation in torsio n. Clinical Relevance-Double plate fixation is biomechanically superior to int erlocking nail fixation in vitro in ostectomized equine MC3 bones. (C) Copy right 1999 by The America, College of Veterinary Surgeons.