ABSTRACT
Objective To study biomechanical properties such as range of motion (ROM), intervertebral disc stress, ligament tension of inferior cervical spinal segment after the treatment of Discover, Prodisc-C artificial intervertebral disc replacement, and anterior cervical discectomy and fusion (ACDF), as well as mechanical property changes of the prosthesis after implantation. Methods Three kinds of operation plan on C5-6 cervical disc degeneration were established: Discover model, Prodisc-C model and ACDF model, as well as C4-7 segment original model of cervical vertebra. Biomechanical property changes after operation in cervical spine C4-7 segment in sagittal, coronal and transverse section were analyzed. Results ROM changes of cervical segment C5-C6 were as following: in Discover model it increased by 12.7%-73.1%, Prodisc-C model increased by 74%-98%, ACDF decreased by 55.8%-71.8%. The stress of C4-5 intervertebral disc after Discover artificial disc replacement showed no obvious increase, while the stress of C6-7 intervertebral disc decreased by 33.2%-54.2% under flexion, extension and axial rotation conditions. The amplification of ligament tension in Discover model decreased by 30%-40% as compared to that in Prodisc-C model. The maximum stress of Discover model (36.72 MPa) appeared under flexion condition, which was smaller than that in Prodisc-C model. Conclusions Artificial disc replacement can help to keep movement performance for segment after surgery. As a newly developed artificial intervertebral disc prosthesis, Discover makes some progress in the aspect of decreasing ligament stress and maintaining spinal stability. The research findings will provide theoretical basis for the clinical study on ACDF and artificial cervical intervertebral disc replacement surgeries.
ABSTRACT
Objective To establish 3D finite element of human cervicothoracic spine C5-T2 based on CT images, and explore effects on stability of the cervicothoracic spine after total spondylectomy (TS) by using various combinations of internal fixation devices (pedicle screw, titanium mesh, steel plate), including the stress distributions on these internal fixation devices. Methods The intact finite element model of cervicothoracic spine C5-T2 was established and validated by comparing the model’s range of motion (ROM) with that of other in vitro experiments. Then four reconstruction models after TS of cervical spine segment C7 were established: TM+AP+DPS model (titanium mesh + anterior plate + posterior double-segmental pedicle screw), TM+AP+SPS model (titanium mesh + anterior plate + posterior single-segmental pedicle screw), TM+DPS model (titanium mesh + posterior double-segmental pedicle screw), AP+DPS model (anterior plate + posterior double-segmental pedicle screw). ROM of each reconstruction model under flexion, extension, lateral bending and rotation and stress distributions on these internal fixation devices were then analyzed. Results ROM of the reconstruction segments was greatly reduced by over 93% as compare to that of the intact model. Stress concentration phenomenon appeared on the titanium mesh in the TM+AP+SPS model. Conclusions The fixation effects of four reconstruction models are similar. Stresses on 3 DPS fixed-models are more evenly distributed, indicating that the overall stability of DPS fixed-model is superior to that of SPS fixed-model.
ABSTRACT
Objective To establish a 3D finite element model of cervicothoracic spinal segments C5-T2 based on CT images and test its validity and effectiveness. Methods By using the Mimics, Geomagic and Hypermesh software, the 3D model of cervicothoracic spinal segments C5-T2 was reconstructed, repaired and pre-processed. Moment of ±0.5, 1, 1.5, 2 N•m were applied on top of the model to simulate loads produced during the flexion and extension movement of human body. The range of motion (ROM) of the segments C5-T2 during flexion and extension was calculated by ANSYS, and the reliability of the model was verified by comparing the experimental results in the previous literature with the finite element analysis results obtained in this study. Results Under the moment of 1 N•m, the ROMs of C5-6, C6-7, C7-T1 and T1-2 during flexion were 4.30°,3.21°,1.66° and 1.41°, and those during extension were 3.47°, 2.86°, 0.96° and 0.92°, respectively. The maximum stress during flexion appeared on the front of the vertebral body, while that during extension appeared on the back of the vertebral body. The trends of ROM and stress distributions were consistent with results reported in the previous literature. Conclusions The 3D model established in this study is accurate and realistic, and conforms to biomechanical properties of the cervicothoracic spine. The simulation results can be further used to explore clinical pathology of the spine and provide theoretical references for evaluation on cervicothoracic spine surgery.