Finite element analysis of the stress distribution in small joint after the implantation of artificial lumbar intervertebral disk

Yichun XU; Shangli LIU; Meichao ZHANG; Daozhang CAI

ABSTRACT

BACKGROUND:

Presently-used artificial intervertebral disk is different greatly from the normal physiological intervertebral disk in structure, material and biological properties and so on. Therefore, stress conduction at corresponding spinal section will have a certain change after the implantation of artificial intervertebral disk.

OBJECTIVE:

To investigate the stress distribution in small joints of normal intervertebral disk group, vertebral extirpation group and artificial lumbar intervertebral disk group with three-dimensional element method in order to discuss exploratorily the influence of the implantation of artificial lumbar intervertebral disk on the stress distribution in small joints.

DESIGN:

Observative and comparison experiment.

SETTING:

Orthopedic Department, Third Affiliated Hospital and Second Affiliated Hospital, Sun Yat-sen University; Biomechanical Laboratory in Southern Medical University.

PARTICIPANTS:

Spinal specimen collected from the healthy people who died in accidenct without any spinal illness (donated by their family member) was used to establish three kinds of three-dimensional element models of normal intervertebral disk, artificial intervertebral disk and vertebral extirpation as experimental subjects.

METHODS:

Finite element MSC.MARK software was used to establish normal intervertebral disk model with height of 10.00 mm, cross sectional area of 1300.00 mm2, and vertebral pulp cross sectional area of 495.8 mm2;in the model of vertebral pulp extirpation,the intrinsic pressure of vertebral pulp was zero; and in the three dimensional models of artificial lumbar intervertebral disk and L4-5 movement segment , the small joints were about 10.53 mm high with width of 13.37 mm and auricular area of 135 mm2.Then lumbar movement was simulated for the study of the stress distribution in small joint.MAIN OUTCOME

MEASURES:

Comparison of the stress in small joints under 6 kinds of states in the above three kinds of intervertebral disk movement model.

RESULTS:

In vertebral pulp extirpation group, the stress was proved to be the highest at superior edge, posterior middle part, lower edge and anterior middle part of small joints under anteflexion, backward extension, compression, lateroflexion and revolving states, moreover, small joint stress in artificial lumbar intervertebral disk was higher than that in normal intervertebral disk, but obviously lower than that in vertebral pulp extirpation group;however, the small joint of the middle part of artificial lumbar intervertebral disk bore the highest stress under revolving states.

CONCLUSION:

In contrast with vertebral pulp extirpation group, the small joint stress could be reduced after the implantant of artificial lumbar intervertebral disk, but was still higher than that of normal lumbar intervertebral disk group and the anti-verticity in artificial lumbar intervertebral disk group was markedly lower than that of normal lumbar intervertebral disk group and vertebral pulp ablation group, thus indicating that although presently-used artificial lumbar intervertebral disk possesses most of mechanical functions of normal lumbar intervertebral disk, but is still different from true lumbar intervertebral disk.