Abstract:

BACKGROUND: Nowadays, most of three-dimensional finite analysis concern normal lumbar vertebra models in spinal surgery. Few researches have been conducted regarding models of postoperative pathological state.
OBJECTIVE: To develop a three-dimensional finite element model of posterior fusion surgery of L _4-5 spondylolysis to evaluate the stability and the stress distributions of pedicle screw and cage in different models.
METHODS: The L _4-5 motion segment data were obtained from CT scans of the lumbar spine of an adult man with spondylolysis. The three-dimensional finite element model of L _{4 -5} spondylolysis was established by abaqus6. 51. The models were subjected to gridding and attribute assignment. The finite element models of pedicle screw and cage were also established, and various posterior fusion models of different approaches were created according to the clinical operation types. The boundary was set, and the models were subjected to different forces including axial compressive, anterior bending, posterior extension, left bending, and right rotation. The von Mises stress, displacement of the fusion segments on the pedicle screw and cages were recorded. All the measuring data were analyzed by SPSS 13.0.
RESULTS AND CONCLUSION: All the stress mostly concentrated in the joint position of the arch bar and screw fixed. The stress was minimal under axial compression and maximal under axial rotation. The stress of the Cage mainly located in the anterior part and posterior parts. The displacement of posterior fusion was less than the lateral fusion (P < 0.05). A three-dimensional finite element model of different posterior fusion methods for L₄ spondylolysis was established, and the stress distribution and displacement was clinically significant under loading. The stability of lumbar interbody fusion was better than pedicle screw fixation plus lateral fusion.