L_5/S_1轴向联合斜向螺钉内固定术的生物力学研究

目的通过研究后方双侧斜向螺钉,轴向螺钉联合后方双侧斜向螺钉和椎弓根螺钉钉棒系统3种内固定方式的生物力学性能,探索轴向螺钉联合后方双侧斜向螺钉是否满足L5/S1内固定生物力学稳定性的要求。方法取9具成人新鲜尸体腰椎标本(生前无脊柱疾病史),进行骨密度测量,排除骨质疏松病变;并进行X线扫描,排除解剖学异常。剔除标本上的肌肉组织,保留椎间盘、韧带及骨性结构的完整性。将标本随机分为后方双侧斜向螺钉组(A组)、轴向螺钉联合后方双侧斜向螺钉组(B组)及椎弓根螺钉钉棒系统组(C组)。用牙托粉对标本L5和S1端椎体部分包埋,在生物力学机上完成前屈后伸、左右侧曲及轴向旋转实验。记录施加载荷时椎体前屈后伸、左右侧曲条件下的位移和轴向旋转的角度,完成9具标本的测试与记录。所有的测量数据应用SPSS 19.0软件进行统计学分析。结果在前屈后伸实验中,载荷范围内3组椎体的位移随载荷的增加而增加,在最大载荷下各组间差异有统计学意义(P0.05)。进行两两比较发现,A组和B组差异有统计学意义(P0.05),A组和C组差异有统计学意义(P0.05),B组和C组差异无统计学意义(P0.05)。在左右侧曲实验中,载荷范围内3组椎体的活动度随载荷的增加而增加,在最大载荷下3组间差异无统计学意义(P0.05)。在轴向旋转实验中,扭矩范围内3组旋转角度随扭矩的增加而增加,在最大扭矩下分析各组旋转角度,3组间差异无统计学意义(P0.05)。结论轴向联合后方双侧斜向螺钉内固定能够达到与椎弓根钉棒系统接近的生物力学稳定性。后方双侧斜向螺钉在左右侧曲及轴向旋转方面具有相对稳定的生物力学特性,联合应用轴向螺钉可使L5/S1获得更强的稳定性。

Biomechanical study of novel bilateral oblique screw combined axial screw in L5/S1 internal fixation

Objective To investigate the biomechanical properties of 3 different L₅/S₁ internal fixations, including bilateral oblique screw fixation, bilateral oblique screw combined axial screw fixation and pedicle screw fixation. Methods Nine fresh cadaver lumbar spine specimens with no history of spinal diseases were obtained. Bone mineral density was tested to exclude osteoporosis, and roentgenograph was examined to exclude abnormal anatomy. The muscle tissue was dissected, and the integrity of intervertebral discs, ligaments and bony structure were preserved. The specimens were randomly divided into 3 groups:bilateral oblique screw fixation group (Group A), bilateral oblique screw combined axial screw fixation group (Group B) and pedicle screw fixation group (Group C). Both L₅ and S₁ ends of the specimens were embedded with denture acrylic. Then, flexion and extension, left and right lateral bending and axial rotation tests were performed by biomechanical testing machine. The displacements and rotative angles were recorded, and the data were input into the SPSS 19.0 software for statistical analysis. Results In the flexion and extension test, the displacements among 3 groups showed statistically significant difference (P<0.05). In comparison with each other, there was statistically significant difference between Group A and Group B (P<0.05), Group A and Group C (P<0.05). However, there was no statistically significant difference between Group B and Group C (P>0.05). In the displacements of left and right lateral bending test, no statistically significant difference was observed among the 3 groups (P>0.05).In rotative angles of the left and right rotation, no statistically significant difference was observed among the 3 groups (P>0.05). Conclusion The study suggests that bilateral oblique screw combined axial screw fixation has the similar biomechanical properties to pedicle screw fixation. Bilateral oblique screw fixation has comparable biomechanical properties in lateral bending and axial rotation, but not in flexion and extension. The axial screw fixation can provide better anti-flextion and extension biomechanical properties to the bilateral oblique screw fixation in L₅/S₁ level.