经口咽前路寰枢椎复位钢板内固定的生物力学研究

Biomechanical experiment on transoral atlantoaxial reduction plate

目的研究经口咽前路寰枢椎复位钢板（TARP）的三维运动范围和螺钉拔出力的生物力学。方法12例C0～C3新鲜标本，6例用于三维运动测试，分七组：①完整标本（对照）组，②损伤组（去除C1前弓、C2齿突，破坏关节囊和横韧带等），③TARP组，④后路Brooks钢丝组，⑤Magerl经关节螺钉组，⑥Magerl＋Brooks组，⑦前路经枢椎体寰椎侧块螺钉组，分别测量其三维运动范围（ROM）。另6例（双侧，n=12）分解为单个椎体后用于螺钉拔出力测试，分三组：①寰椎组，②枢椎组，③C3（对照）组，测定最大拔出力、钉道长度和屈服长度。结果TARP组和Magerl＋Brooks组在各个方向上差异均无统计学意义（P〉0．05），前者的ROM值略大于后者，二者抗屈伸、侧屈和旋转均强于其他三种内固定方法（P〈0．05）。寰椎与枢椎、寰椎与C3，的最大拔出力之间差异均有统计学意义（P〈0．05），枢椎和C3，椎体最大拔出力之间差异无统计学意义（P〉0．05）[最大拔出力分别为C1=（491．58±67．92）N，C2=（396．73±60．99）N，C3=（385．53±96．77）N]。寰椎与枢椎、寰椎与C3椎体的钉道长度之间差异均有统计学意义（均为P〈0．05），枢椎和C3椎体钉道长度之间差异无统计学意义（P〉0．05）。三组的屈服长度之间差异无统计学意义（P〉0．05）。C1～C3的螺钉最大拔出力与钉道长度和屈服长度均呈显著正相关（P〈0．05，r分别为0．810和0．652），但与钉道长度的相关性更高（P〈0．05）。结论TARP与目前临床应用的后路Magerl＋Brooks术式等效，较其他三种固定方式（前路经枢椎体寰椎侧块螺钉、后路Magerl经关节螺钉和后路Brooks钢丝固定）具有更坚强的固定作用。TARP的寰椎和枢椎固定螺钉固定牢靠，钉道长度即进钉深度是影响螺钉抗拔出力的主要因素，屈服长度是影响螺钉拔出力的次要因素。

Objective To study biomechanical stability, including rang of motion （ROM） and pull-out strength of screws, of transoral atlantoaxial reduction plating （TARP） . Methods Twelve fresh C0-C3 spine specimens were harvested. Six specimens were designed to compare ROM of TARP in 4 clinical anterior-posterior atlantoaxial arthrodeses in 7 groups： intact （control）, injured, TARP, Brooks, Magerl, Magerl ＋ Brooks, and anterior transarticular screw fixation through C2 vertebral body. The other 6 specimens （totally 12 sides） were designed to compare pull-out strength of screws, screw path length and failure length of C1, C2 and C3 in 3 groups： atlas, axis, and C3 （control）. Results No statistically significant difference in ROM was observed between TARP and Maged ＋ Brooks （P〉0.05）, with the ROM of TARP slightly wider than that of the latter. The ROM of flexion-extension, lateral bending and axial rotation of the above 2 were smaller than those of the other 3 fixators （P〈0.05） . There were statistically significant differences in screw pull-out strength and screw path length between C1 and C2 and C3 （Pull-out strength： C1=491.58±67.92 N, C2=396.73±60.99N, C3 =385.53±96.77 N） （P〈0.05）. No statistically significant differences were observed in screw pull-out strength and path length between C2 and C3 （P〉0.05）. There was no significant difference in screw failure length between C1-C3 （P〉0.05）. The screw pull-out strength was positively correlative to the path length and failure length （correlation coefficients： r=0.810 and r=0.652 respectively） （both P〈0.05）.The screw pull-out strength was more correlative to the path length than to the failure length （P〈0.05）. Conclusions Experimentally, TARP has the same effect with Magerl＋ Brooks and they provide more stability than the other 3 widely used atlantoaxial fixators： Magerl, Brooks and anterior transarticular screw fixation through C2 vertebral body. The TARP screws of C1 and C2 are strong enough for atlanto-axial arthrodesis. Screw path length and failure length are important factors influencing screw pull-out strength.