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Posterior decompressive techniques including one- and two-level laminotomies and laminectomies are often used in treating cervical stenosis. Previously, several in vitro studies were conducted to help us understand the biomechanical changes occurring in the cervical spine after these surgical techniques. However, changes in the intersegmental flexibility under combined flexion-extension remain unclear. In this study, a 3-D nonlinear intact model of the C2–C7 was developed to evaluate the influence of one- and two-level laminotomies and laminectomies on the intersegmental moment rotational responses and internal stresses. The intact model was validated by comparing the predicted responses against experimental data. The validated model was then modified to simulate various surgical techniques for finite element analysis. Results showed that one- and two-level laminectomies increase the C2–C7 rotation motions by about 15% and 20%, respectively. The predicted increase in rotational motions also correlated well with the published data. Furthermore, results indicated that laminectomies would influence the biomechanical responses on both the affected and adjacent motion segments. In contrast, laminotomies have no significant effects on cervical biomechanics. To conduct a one-level laminectomy study, current findings indicate that it takes at least five motion segments to capture the immediate postsurgical biomechanical changes accurately and realistically. Minimally invasive cervical spine surgeries with one- or two-level laminotomies are preferred over one- and two-level laminectomies. Also, there is no consideration as to the efficacy of the two techniques in decompressing the spinal cord or nerve roots, which is the goal of the surgery, but is not examined in this study.
The authors are with the School of Mechanical and Production Engineering, Nanyang Technological University, Nanyang Ave., Singapore 639798.