退变性椎间盘应力分布变化的有限元分析

Stress distribution in the degenerative lumbar disc, a finite element analysis

目的:分析退变性腰椎间盘在不同生理载荷下应力分布的变化情况。方法:建立正常人体L3~S1三维有限元模型及L4/5椎间盘退变模型,导入Ansys软件进行分析,在L3椎体上表面施加500N压力模拟轴向压缩,施加10Nm的力矩模拟腰椎前屈、后伸、侧屈和旋转等各种生理载荷,测量不同载荷下正常与退变椎间盘不同部位的应力,分析退变椎间盘应力分布变化的情况。结果:正常椎间盘垂直载荷时椎间盘应力集中于椎弓根附近,应力最大的分区中压力为29.649N;各种屈曲位时,屈曲侧应力较高,分区中压力最高为59.514N,向对侧逐渐减少,拉力最高为32.686N。相同载荷下,退变椎间盘应力分布发生了变化,髓核压力由45.170~55.308N降至5.471~8.046N;纤维环压力增加,内层纤维环由80.379~95.923N增加至98.898~120.557N,中层纤维环由107.160~140.983N增加至118.549~156.827N,外层纤维环由160.872~204.867N增加至169.302N^216.298N。结论:椎间盘退变后其髓核和纤维环的应力分布会发生变化,在总应力变化不大的前提下,髓核所受应力明显减小,而纤维环所受应力则相应增加,尤以内层和中层纤维环为主。这可能是椎间盘突出和椎间盘源性腰痛的原因之一。

Objectives： To analyze the stress distribution in the degenerative disc under 5 different physiological loadings. Methods： A three-dimensional finite element model of the normal human lumbar spine was established. Three spinal segments（L3-S1） were used to investigate and were modified to simulate a mild to moderate degenerative disc at the L4/5 lumbar level. The 3D finite element models were imported into Ansys software and analyzed. 500N pressure was added on the upper surface of L3, a toque of 10Nm moments was loaded to simulate lumbar axial compression, flexion, extension, lateral bending and rotation. The stress distributions in degenerative and normal discs were measured and analyzed. Results： Under the axial compression, the stress in healthy disc concentrated near the pedicle, with the maximum compressive force of 29.649N. Under the lateral bending, the stress concentrated in the concave side with the maximum compressive force of 59.514N. The stress gradually transferred to the contralateral side with the tensile force of 32.686N. Under the presence of disc degeneration, the stress distribution changed. The force on the nucleus pulposus decreased from 45.170-55.308N to 5.471-8.046N, and at the same time the force on the fibrous ring increased. The force on the inner layer increased from 80.379-95.923N to 98.898-120.557N, the force in the middle layer increased from 107.160-140.983N to 118.549-156.827N, and the force in outer layer increased from 160.872-204.867N to 169.302-216.298N. Conclusions： Under the presence of degeneration, the stress distribution changes. Though the total stress is almost the same, the stress on the nucleus pulposus significantly decreases and the stress on the fibrous ring increases relatively, especially on the inner and the middle fibrous. The fibrous ring is easy to suffer injury due to uneven stress distribution in disc, which remains one of the mechanism of disc herniation and disc originated pain.