McBride A D, Mukherjee D P, Kruse R N, Albright J A
Department of Orthopaedic Surgery, Louisiana State University Medical Center, Shreveport, USA.
Spine (Phila Pa 1976). 1995 Sep 1;20(17):1855-9; discussion 1859-60. doi: 10.1097/00007632-199509000-00001.
This study examined the torsional and shear stiffness of Type II odontoid fractures that were stabilized with two 3.5-mm cannulated AO screws or a single 4.5-mm cannulated Herbert screw.
To determine the stability of a commonly used two-screw method versus a single-screw fixation method. Insertion of a single screw could make the procedure technically easier.
Biomechanical studies have shown the 4.5-mm Herbert screw to generate greater compressive forces than 3.5-mm cannulated screws, which are commonly used to anteriorly stabilize Type II odontoid fractures. No previous biomechanical studies have compared the shear or torsional stiffness of Type II odontoid fractures stabilized with these screws.
Twelve cadaver C2 vertebrae were harvested and an osteotomy was performed to simulate a Type II fracture pattern. Six were stabilized with two 3.5-mm cannulated screws, and the remaining were stabilized with a single 4.5-mm cannulated Herbert screw. Each specimen then was tested in torsion through +/- 0.75 degrees, +/- 1.25 degrees, and +/- 1.75 degrees for 10 cycles each. Shear forces then were applied from an anterior to posterior direction to a maximum load of 44.48 N.
The mean torsional stiffness for the Herbert screw was 1196 N.m/deg, which was significantly greater than the mean stiffness of the 3.5-mm screw fixation, which measured 434 N.m/deg. The mean shear stiffness for the Herbert screw fixation was 106.9 kN/m, compared to 86.1 kN/m for the 3.5-mm cannulated screw. This was not statistically significant.
The biomechanical properties of the 4.5-mm cannulated Herbert screw suggest it may lend itself for use in fixation of Type II odontoid fractures. With only a single screw to insert, this technically demanding procedure may be less daunting.
本研究检测了用两枚3.5毫米空心AO螺钉或一枚4.5毫米空心Herbert螺钉固定的II型齿状突骨折的扭转刚度和剪切刚度。
确定常用的双螺钉固定法与单螺钉固定法的稳定性。插入单枚螺钉可使手术在技术上更简便。
生物力学研究表明，4.5毫米Herbert螺钉比常用于前路固定II型齿状突骨折的3.5毫米空心螺钉能产生更大的压缩力。此前尚无生物力学研究比较过用这些螺钉固定的II型齿状突骨折的剪切刚度或扭转刚度。
采集12具尸体的C2椎体，进行截骨以模拟II型骨折模式。6例用两枚3.5毫米空心螺钉固定，其余用一枚4.5毫米空心Herbert螺钉固定。然后对每个标本进行扭转测试，分别以±0.75度、±1.25度和±1.75度扭转10个周期。然后从前向后施加剪切力，最大载荷为44.48牛。
Herbert螺钉的平均扭转刚度为1196牛·米/度，显著大于3.5毫米螺钉固定的平均刚度，后者为434牛·米/度。Herbert螺钉固定的平均剪切刚度为106.9千牛/米，而3.5毫米空心螺钉为86.1千牛/米。这一差异无统计学意义。
4.5毫米空心Herbert螺钉的生物力学特性表明，它可能适用于II型齿状突骨折的固定。由于只需插入一枚螺钉，这个技术要求较高的手术可能就不那么令人望而却步了。
