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

English Keywords:Intervertebral disc  Degeneration  Biomechanics  Finite element analysis

English Abstract:

  【Abstract】 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.