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The effects of single-level instrumented lumbar laminectomy on adjacent spinal biomechanics.

ABSTRACT: Study Design Biomechanical study. Objective Posterior instrumentation is used to stabilize the spine after a lumbar laminectomy. However, the effects on the adjacent segmental stability are unknown. Therefore, we studied the range of motion (ROM) and stiffness of treated lumbar spinal segments and cranial segments after a laminectomy and after posterior instrumentation in flexion and extension (FE), lateral bending (LB), and axial rotation (AR). These outcomes might help to better understand adjacent segment disease (ASD), which is reported cranial to the level on which posterior instrumentation is applied. Methods We obtained 12 cadaveric human lumbar spines. Spines were axially loaded with 250 N for 1 hour. Thereafter, 10 consecutive load cycles (4 Nm) were applied in FE, LB, and AR. Subsequently, a laminectomy was performed either at L2 or at L4. Thereafter, load-deformation tests were repeated, after similar preloading. Finally, posterior instrumentation was added to the level treated with a laminectomy before testing was repeated. The ROM and stiffness of the treated, the cranial adjacent, and the control segments were calculated from the load-displacement data. Repeated-measures analyses of variance used the spinal level as the between-subject factor and a laminectomy or instrumentation as the within-subject factors. Results After the laminectomy, the ROM increased (+19.4%) and the stiffness decreased (-18.0%) in AR. The ROM in AR of the adjacent segments also increased (+11.0%). The ROM of treated segments after instrumentation decreased in FE (-74.3%), LB (-71.6%), and AR (-59.8%). In the adjacent segments after instrumentation, only the ROM in LB was changed (-12.9%). Conclusions The present findings do not substantiate a biomechanical pathway toward or explanation for ASD.

SUBMITTER: Bisschop A

PROVIDER: S-EPMC4303474 | biostudies-other | 2015 Feb

REPOSITORIES: biostudies-other

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Project description:BackgroundAlthough it is critical to understand the accelerated degeneration of adjacent segments after fusion, the biomechanical properties of the spine have not been thoroughly studied after various fusion techniques. This study investigates whether four Roussouly's sagittal alignment morphotypes have different biomechanical characteristics after different single- or double-level spinal fixations.MethodsThe parametric finite element (FE) models of Roussouly's type (1-4) were developed based on the radiological data of 625 Chinese community population. The four Roussouly's type models were reassembled into four fusion models: single-level L4-5 Coflex fixation model, single-level L4-5 Fusion (pedicle screw fixation) model, double-level Coflex (L4-5) + Fusion (L5-S1) model, and double-level Fusion (L4-5) + Fusion (L4-5) model. A pure moment of 7.5 Nm was applied to simulate the physiological activities of flexion, extension, lateral bending and axial rotation.ResultsBoth single-level and double-level spinal fixation had the greatest effect on lumbar range of motion, disc pressure, and annulus fibrosis stress in flexion, followed by lateral bending, extension, and axial rotation. In all models, the upper adjacent segment was the most influenced by the implantation and bore the most compensation from the fixed segment. For Type 2 lumbar, the L4-L5 Coflex effectively reduced the disc pressure and annulus fibrosis stress in adjacent segments compared to the L4-L5 Fusion. Similarly, the L4-L5 Coflex offered considerable advantages in preserving the biomechanical properties of adjacent segments for Type 1 lumbar. For Type 4 lumbar, the L4-L5 Coflex did not have superiority over the L4-L5 Fusion, resulting in a greater increase in range of motion at adjacent segments in flexion and extension. The difference between the two fixations was not apparent in Type 3 lumbar. Compared to the single-level Fusion, the changes in motion and mechanics of the lumbar increased after both the double-level Coflex + Fusion and Fusion + Fusion fixations, while the differences between two double-level fixation methods on adjacent segments of the four lumbar models were similar to that of the single-level fixation.ConclusionType 3 and Type 4 lumbar have good compensatory ability and therefore allow for a wider range of surgical options, whereas surgical options for small lordotic Type 1 and Type 2 lumbar are more limited and severe.

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The effects of single-level instrumented lumbar laminectomy on adjacent spinal biomechanics.

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