小型猪脊柱短节段经椎弓根内固定后椎间盘压强变化研究

Biomechanical study of intensity of pressure of intervertebral disc after short segment unilateral pedicle screw fixation in Chinese mini-pigs

目的通过对椎弓根钉棒系统固定的小型猪特征脊柱节段的椎间盘进行生物力学研究,探究其对于椎间盘压力分布的影响和规律。方法截取6具6周龄小型猪特征性脊柱节段:T3~4、T11~12、T15~L1、L3~4、L4~5节段及其相邻上下椎体,制作各节段实验模型,连接至生物力学实验机,加载载荷200 N,分别在垂直、5°前屈、5°后伸和5°侧弯运动等状态下进行加压,并获取相应压敏片图像作为未固定组;然后在上述节段行单侧椎弓根内固定,重复生物力学测试获得固定组数据。应用光密度计读取并分析每个压敏片的压强。结果在垂直加压、5°前屈、5°后伸3个载荷条件下,固定组T3~4、T11~12、T15~L1、L3~4、L4~5的后侧椎间盘压强与未固定组相应节段、相应载荷条件相比均明显减小,差异均有统计学意义;固定组T3~4、T11~12、T15~L1、L3~4、L4~5固定侧压强与未固定组相应节段、相应载荷条件相比均明显减小,差异均有统计学意义;侧弯时固定组T3~4、T11~12、T15~L1、L3~4、L4~5凹侧椎间盘压强分别为(0.83±0.12)、(0.93±0.12)、(0.50±0.05)、(0.60±0.10)、(0.55±0.08)MPa,均小于未固定组的(1.70±0.18)、(1.79±0.14)、(1.84±0.22)、(1.74±0.28)、(1.60±0.23)MPa,差异均有统计学意义。固定组在垂直加压、5°前屈、5°后伸的整体椎间盘压强均较未固定组明显减小,差异均有统计学意义。结论在各载荷条件下,短节段经椎弓根内固定均可有效减小固定侧椎间盘的压强,改变椎间盘整体的受力分布,减小后侧椎间盘压强。

Objective To explore the mechanical changes and distributions of pressure in each characteristic intervertebral disc after short segment unilateral pedicle screw fixation in Chinese mini-pigs. Methods Six characteristic spine segments of 6-week-old Chinese mini-pigs (T3-4、T11-12、T15-L1、L3-4、L4-5 segments with adjacent upper and lower vertebrae) were chosen as experimental models. A biomechanical machine and pressure sensitive film were used to measure the pressure on the vertebral columns when they were subjected to pressures of 200 N as unfixed group. Compression was carried out under vertical, 5 °flexion, 5 °extension and 5 °lateral bending, respectively. Then the PCF (posterior cervical fixation) system were fixed on all segments (left side) as fixed group , and biomechanical tests were repeated to obtain data. A Fujitsu densitometer (Japan) was used to measure the pressure on each direction of the pressure sensitive film. Results In vertical pressures, 5° flexion and 5°extension conditions,the posterior pressure of T3-4、T11-12、T15-L1、L3-4 and L4-5 intervertebral discs were decreased after fixation,the differences were statistically significant;The fixed side pressures of T3-4、T11-12、T15-L1、L3-4 and L4-5 in the fixed group were significantly lower than those in the unfixed group in the corresponding segments and load conditions, and the differences were statistically significant. The concave disc pressures of T3-4、T11-12、T15-L1、L3-4 and L4-5 in the fixed group were 0.83±0.12, 0.93±0.12, 0.50±0.05, 0.60±0.10 and 0.55±0.08 MPa respectively, which were lower than those of the unfixed group 1.70±0.18, 1.79±0.14, 1.84±0.22, 1.74±0.28, 1.60±0.23 MPa, and the differences were statistically significant. The total disc pressure of the fixed group was significantly lower than that of the non-fixed group in vertical compression, 5 degree flexion and 5 degree extension, and the differences were statistically significant. Conclusion Unilateral pedicle screw fixation can decrease the pressure on fixed side of fixed group in all conditions and change the distribution of pressure. The posterior pressure decreased particularly. Short-segment unilateral pedicle screw fixation can decrease the average pressure of intervertebral disc, which is an excellent surgery in curing scoliosis in young children.