Investigation of Stresses Developed in Natural and Implanted Human Cervical Spine by Finite Element Method

Background: For design of suitable spinal implants, computational investigation of stresses developed within spine as a result of implantation is very important. Hence, the present study has been carried out for computation of stresses developed within Cervical Spine area during various neck motions using Finite Element method, for natural spine as well as for spines with implantation of both types viz Fusion Surgery and Total Disc Replacement. Methods: Computerized Tomography (CT) scan data of Indian people have been collected from hospitals. Important properties viz Elastic Modulus (E) and Density (ρ) of bones have been extracted from CT scan data for development of models for stress analysis. Bones with varying ‘E’ and ‘ρ’ values have been classified in five different categories. Under applied moments of 0.6 N-m, 1.2 N-m, 1.8 N-m and 2.4 N-m stress patterns have been computed for all six possible motions in (a) Natural Cervical Spine (b) Cervical Spine with Fusion Surgery (FS) and (c) Cervical Spine with Total Disc Replacement (TDR). Results: Stresses in all regions for natural spine have been found to be lowest compared to spines with FS and TDR. Stresses generated within spines with TDR are in between of those with FS and natural spine for some regions whereas for other adjacent regions stresses generated for spines with TDR are highest. Stress values declined steadily with respect to increase in bone strength for cervical spines with FS. Conclusion: Stresses developed are lower with TDR than with FS in all regions except in close vicinity of implanted artificial disc.