An in vitro biomechanical comparison of hydroxyapatite coated and uncoated ao cortical bone screws for a limited contact: dynamic compression plate fixation of osteotomized equine 3rd metacarpal bones

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OBJECTIVES: To compare the monotonic biomechanical properties of a broad 4.5 mm limited contact-dynamic compression plate (LC-DCP) fixation secured with hydroxyapatite (HA) coated cortical bone screws (HA-LC-DCP) versus uncoated cortical bone screws (AO-LC-DCP) to repair osteotomized equine 3rd metacarpal (MC3) bones. STUDY DESIGN: Experimental. SAMPLE POPULATION: Adult equine cadaveric MC3 bones (n = 12 pair). METHODS: Twelve pairs of equine MC3 were divided into 3 test groups (4 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. For the HA-LC-DCP-MC3 construct, an 8-hole broad LC-DCP (Synthes Ltd, Paoli, PA) was secured on the dorsal surface of each randomly selected MC3 bone with a combination of four 5.5 mm and four 4.5 mm HA-coated cortical screws. For the AO-LC-DCP-MC3 construct, an 8-hole 4.5 mm broad LC-DCP was secured on the dorsal surface of the contralateral MC3 bone with a combination of four 5.5 mm and four 4.5 mm uncoated cortical screws. 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 HA-LC-DCP fixation were significantly greater than those of the AO-LC-DCP fixation. Mean ± SD values for the HA-LC-DCP and the AO-LC-DCP fixation techniques, respectively, in single cycle to failure under 4 point bending were: yield load, 26.7 ± 2.15 and 16.3 ± 1.38 kN; yield bending moment, 527.4 ± 42.4 and 322.9 ± 27.2 N-m; composite rigidity, 5306 ± 399 and 3003 ± 300 N-m/rad; failure load, 40.6 ± 3.94 and 26.5 ± 2.52 kN; and failure bending moment, 801.9 ± 77.9 and 522.9 ± 52.2 N-m. Mean cycles to failure in 4 point bending of the HA-LC-DCP fixation (116,274 ± 13,211) was significantly greater than that of the AO-LC-DCP fixation 47,619 ± 6580. Mean yield load, mean composite rigidity, and mean failure load under torsional testing, single cycle to failure was significantly greater for the broad HA-LC-DCP fixation compared with the AO-LC-DCP fixation. In single cycle to failure under torsion, mean ± SD values for the HA-LC-DCP and the AO-LC-DCP fixation techniques, respectively, were: yield load, 101.3 ± 14.68 and 70.54 ± 10.20 N-m; composite rigidity, 437.9 ± 32.9 and 220.7 ± 17.6 N-m/rad; and failure load: 105.7 ± 15.5 and 75.28 ± 10.1 N-m. CONCLUSION: HA-LC-DCP was superior to AO-LC-DCP in resisting the static overload forces (palmarodorsal 4 point bending and torsional) and in resisting cyclic fatigue under palmarodorsal 4 point bending.

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Veterinary surgery : VS

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