Artikel
Flexibility, cage loading and sagittal alignment in a defect model of the cervicothoracic junction
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Veröffentlicht: | 4. Juni 2012 |
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Objective: Surgical treatment of defects within the cervicothoracic junction (CTJ) is often complicated by implant failure. The objective of the study was to analyse, how different implants influence flexibility, cage loading, and sagittal alignment within CTJ. This was done within an isolated anterior defect model of the CTJ.
Methods: 5 human cervical specimens C5-T2 were used with the following surgical modifications: Intact. Following application of an isolated anterior wedge-shape defect within C7 that was forced into failure by flexion-compression loading (Defect). Following vertebral body replacement and anterior plate fixation (Rigid Option of Quintex, Aesculap AG, Tuttlingen, Germany), ACDF. Following ACDF with dynamic loading (ACDF dyn). Following ACDF with pedicle-screw-rod fixation (S4, Aesculap AG, Tuttlingen, Germany), ACDF+Ped. We analysed in each surgical modification: 1. Three-dimensional (flexion-extension, left-right-lateral bending, axial left-right-rotation) flexibility C6–T1; 2. Cage loading during flexibilty test; 3. Lateral x-ray flexibility tests were performed using ±2.5 Nm pure moments in a custom spine tester. Cutting a standardised wedge shaped defect into the vertebral body C7 generated a defect. Failure was induced using a material test machine that applied loading in flexion-compression. Load to displacement graphs were recorded.
Results: Flexibility C6-T1, shown as an example in flexion-extension: Intact: 11.1°±3.5°, ACDF: 8.6°±3.5°, ACDF dyn: 9.4°±4.6°, ACDF+Ped: 5.8°±3.75°. (significant reduction only for ACDF+Ped versus intact, p=0.0497) Cage loading: ACDF and ACDF dyn allows peaks between loading and unloading. However, additional pedicle-screw- fixation (ACDF+Ped) reduces peaks significantly (p=0.003). Sagittal alignment C6-T1: Intact: Lordosis 2.1±5.3°, defect: Kyphosis 6.1±6.5°, ACDF dyn: Kyphosis 2.0±5.3°, ACDF+Ped: Lordosis 1.8±3.2°. Significant changes are noted for intact vs defect, ACDF Ped versus defect, ACDF+Ped vs. ACDF dyn, p=0.043, Wilcoxon Test.
Conclusions: Within this model, an anterior rigid plate does not reduce motility significantly versus the intact spine. Additional pedicle-screw rod fixation, however, does. Moreover, posterior fixation reduces peaks of loading and unloading and restores initial lordoctic alignment. Thus, an additional posterior fixation is useful to avoid implant failure, even if posterior elements are preserved.