Sod Gary A, Hubert Jeremy D, Martin George S, Gill Marjorie S
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA.
Vet Surg. 2006 Oct;35(7):634-42. doi: 10.1111/j.1532-950X.2006.00201.x.
To compare biomechanical properties of a prototype 5.5 mm tapered shaft cortical screw (TSS) and 5.5 mm AO cortical screw for an equine third metacarpal dynamic compression plate (EM-DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones.
Paired in vitro biomechanical testing of cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation.
Adult equine cadaveric MC3 bones (n=12 pairs).
Twelve pairs of equine MC3 were divided into 3 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. An EM-DCP (10-hole, 4.5 mm) was applied to the dorsal surface of each, mid-diaphyseal osteotomized, MC3 pair. For each MC3 bone pair, 1 was randomly chosen to have the EM-DCP secured with four 5.5 mm TSS (2 screws proximal and distal to the osteotomy; TSS construct), two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws in the remaining holes. The control construct (AO construct) had four 5.5 mm AO cortical screws to secure the EM-DCP in the 2 holes proximal and distal to the osteotomy in the contralateral bone from each pair. The remaining holes of the EM-DCP were filled with two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws. All plates and screws were applied using standard AO/ASIF techniques. Mean test variable values for each method were compared using a paired t-test within each group. Significance was set at P<.05.
Mean 4-point bending yield load, yield bending moment, bending composite rigidity, failure load and failure bending moment of the TSS construct were significantly greater (P<.00004 for yield and P<.00001 for failure loads) than those of the AO construct. Mean cycles to failure in 4-point bending of the TSS construct was significantly greater (P<.0002) than that of the AO construct. The mean yield load and composite rigidity in torsion of the TSS construct were significantly greater (P<.0039 and P<.00003, respectively) than that of the AO construct.
The TSS construct provides increased stability in both static overload testing and cyclic fatigue testing.
The results of this in vitro study support the conclusion that the EM-DCP fixation using the prototype 5.5 mm TSS is biomechanically superior to the EM-DCP fixation using 5.5 mm AO cortical screws for the stabilization of osteotomized equine MC3.
比较一款原型5.5毫米锥形杆皮质骨螺钉（TSS）和5.5毫米AO皮质骨螺钉用于马第三掌骨动力加压钢板（EM-DCP）固定修复马第三掌骨（MC3）截骨的生物力学性能。
对有骨干中段截骨的马尸体MC3进行配对体外生物力学测试，通过两种骨折固定方法之一进行稳定。
成年马尸体MC3骨（12对）。
将12对马MC3分为3组（每组4对），分别进行（1）4点弯曲单周期至破坏测试，（2）4点弯曲循环疲劳测试，以及（3）扭转单周期至破坏测试。将一块EM-DCP（10孔，4.5毫米）应用于每对骨干中段截骨的MC3的背侧。对于每对MC3骨，随机选择一根用四颗5.5毫米TSS（截骨近端和远端各两颗螺钉；TSS结构）固定EM-DCP，两颗5.5毫米AO皮质骨螺钉（钢板最近端和最远端的孔），其余孔用四颗4.5毫米AO皮质骨螺钉。对照结构（AO结构）用四颗5.5毫米AO皮质骨螺钉将EM-DCP固定在每对中对侧骨截骨近端和远端的两个孔中。EM-DCP的其余孔用两颗5.5毫米AO皮质骨螺钉（钢板最近端和最远端的孔）和四颗4.5毫米AO皮质骨螺钉填充。所有钢板和螺钉均采用标准AO/ASIF技术应用。每组内使用配对t检验比较每种方法的平均测试变量值。显著性设定为P<0.05。
TSS结构的平均4点弯曲屈服载荷、屈服弯矩、弯曲复合刚度、破坏载荷和破坏弯矩均显著高于AO结构（屈服时P<0.00004，破坏载荷时P<0.00001）。TSS结构4点弯曲的平均破坏循环次数显著高于AO结构（P<0.0002）。TSS结构的平均屈服载荷和扭转复合刚度显著高于AO结构（分别为P<0.0039和P<0.00003）。
TSS结构在静态过载测试和循环疲劳测试中均提供了更高的稳定性。
这项体外研究的结果支持以下结论，即使用原型5.5毫米TSS进行EM-DCP固定在生物力学上优于使用5.5毫米AO皮质骨螺钉进行EM-DCP固定来稳定马MC3截骨。
