Anterior Cervical Decompression and Fusion: Influence of the Instrumented Segment’s Mobility on Adjacent Segmental Biomechanics
Date Issued
2015
Date
2015
Author(s)
Hsieh, Chia-Hao
Abstract
Objective: To investigate the influence of the cervical total range of motion and instrumented segment’s mobility for cervical spine after simulated Anterior Cervical Decompression and Fusion (ACDF) surgery. Introduction: The ACDF surgery is a commonly employed surgical technique to treat Cervical Spondylotic Myelopathy (CSM). Despite the reported high clinical success rates of ACDF, an increased incidence of adjacent segment disease (ASD) post ACDF surgery has raised significant concerns in the literature. Instrumentation fusion after ACDF was regarded as the main reason to accelerate ASD, range of motion compensation will occur in adjacent segment after instrumentation fusion, so the increasing range of motion will couple with intradiscal pressure and stress increase, and leads to ASD. However, instrumentation fusion effectiveness after ACDF is quite different in patients, whether fusion effectiveness after surgery affect cervical column or adjacent segment is not clearly understood. Therefore, this study aims to understand the difference in fusion effectiveness and its subsequent biomechanical influence on the instrumented and adjacent segments. Statistically, paired t-test was used to determine the difference between groups. Material and method: Cervical total range of motion and instrumented segment’s mobility are the two controlled factors in present study. Range of motion (ROM), neutral zone (NZ), disc height (DH), foramen area (FA) and center of rotation (COR) were included as the dependent parameters. This in-vitro study was constructed from 6 porcine cervical (C2-C7). The C4-C5 is designed as the instrumented-level. Cervical total ROM included three groups, standard group (46⁰), low-ROM group (35⁰) and high-ROM group (42⁰), all groups were based on previous in-vivo flexion-extension data. In order to simulate ACDF, lab-design cage and lateral-constraint plates were used to control the mobility of instrumented level. Instrumented segment’s mobility included two groups, one is low-constraint (ROM contribution as 15%) and another is high-constraint (ROM contribution as 5%) For the measurements of parameters, radiographs of the cervical spine were obtained before and after ACDF-simulation. Range of motion and center of rotation calculated from motion trajectory, disc height and foramen were obtained from radiographs, with the neutral zone calculated from the load-displacement curve. Result: Range of motion contribution to instrumented-level significantly decreased and adjacent-levels significantly increased after ACDF-simulation. Neutral zone was different between high-constraint and low-constraint scenarios with 0.5N-m disturbance. Under same constraint, disc height significantly increased in instrumented-level while adjacent-level decreased in anterior and increased in posterior during flexion. Furthermore, for the same range of motion, disc height of adjacent-level decreased in high-constraint group. Foramen area decreased in instrumented-level when instrumented-level was highly-constrained in high-ROM group. After lab-design cage was implanted, the center of rotation in the instrumented-level tended to move anteriorly in comparison with that in adjacent-level. Conclusion: Range of motion compensation was confirmed in every group after ACDF-simulation, 0.5N-m neutral zone demonstrated higher mobility of the cervical spine in high-constraint group. With disc heights of adjacent-levels affected by instrumented-level in higher range of motion or high-constrained scenarios, upper level changed more readily in this study. For clinical application, high-constrain of the cervical spine will improve cervical stability but often coupled with range of motion compensation as well as adjacent disc height.
Subjects
Cervical Spondylotic Myelopathy
in-vitro study
instrumentation
range of motion
biomechanics
Type
thesis
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