Development of Lumbar Surgery from Biomechanical Perspectives / 医用生物力学

Lumbar surgical operation is the crucial treatment against lumbar degenerative diseases (LDDs), whose development depends on persistent comprehension and innovation of vertebral biomechanics. The thorough understanding of biomechanical changes during lumbar senescence and degeneration is the important bedrock to grasp LDDs pathogenesis, renovate LDDs surgical strategy, and embrace more precise and minimally invasive treatment against LDDs. Herein, in this review, the intimate crosstalk between LDDs with degenerative biomechanics of vertebrae, intervertebral disc and paravertebral muscles was elucidated, followed by the classification of lumbar surgery history into non-vertebral implant era (before the year 1980), vertebral implant era (during the year 1980-1990), vertebral fusion era (during the year 1990-2010), precise and minimally invasive decompression era (after the year 2010) based on lumbar surgical characteristics in each era. The significance of representative biomechanical studies in each era for lumbar surgery was also concluded. From biomechanical perspectives, the history of spinal surgery is the development history of surgical strategies that has progressed as the continuously in-depth understanding of spinal biomechanics. With the deepening of spinal biomechanical researches, spinal surgeons are expected to develop treatment strategies that are more adapted to physiological and biomechanical characteristics of the spine, thereby guiding the future direction of spinal surgery advancement.

Retrospect and Prospect on Researches of Spine Biomechanics / 医用生物力学

The study of spine biomechanics is an important foundation for understanding spine function, spine pathogenesis as well as selection of spinal therapeutic approaches. This review summarizes the basic research progress and results of spine biomechanics from five aspects, including the individual components of spine (such as spinal vertebrae), intervertebral discs, ligaments and functional spinal units and the whole spine. All these studies include the in vitro and in vivo experiments on human spinal specimens and animal spinal specimens, and the results of different research methods such as the mathematical model. This review also summarizes some of the poorly understood biomechanical data, which would become an important research direction in the future.

Review on the Progress in Development of Finite Element Models for Functional Spinal Units: Focus on Lumbar and Lumbosacral Levels

@#Functional spinal unit (FSU) has been of major interest in research related to the human spine as it is the simplest entity of spine that is believed to provide vital information useful in analyzing the biomechanics of the spine. In-vitro experiments and in-vivo tests are implemented for this purpose, but due to many restraints in using them, the use of an alternate approach such as Finite Element Analysis (FEA) seems preferential. FEA offers an edge in evaluating significant parameters that may or may not be possible through experiments. The finite element analysis of FSU’s has evolved to handle complexity with the increase in computing capacity and advancement in the software packages. This paper reviews the progress in the development of finite element analysis of FSU’s and also focuses on the application of FEA to analyse the lumbar (L1-L5) and lumbosacral (L5-S1) levels of the spine where spinal disorders are more prevalent.

A biomechanical study on proximal junctional kyphosis following long-segment posterior spinal fusion

Posterior long-segment spinal fusion may lead to proximal junctional kyphosis (PJK). The present study sought to identify the appropriate fusion levels required in order to prevent PJK using finite element analysis. A finite element model was constructed based on the whole-spine computed tomography findings of a healthy adult. Nine commonly used posterior spinal fusion methods were selected. Stress on the annulus fibrosis fibers, the posterior ligamentous complex, and the vertebrae after various spinal fusions in the upright position were compared. This study was divided into two groups: non-fusion and fusion. In the former, the stress between the T10 and the upper thoracic vertebrae was higher. Comparing thoracic and lumbar segments in the fusion group, the peak stress values of the upper instrumented vertebrae (UIV) were mainly observed in T2 and L2 whilst those of the UIV+1 were observed in T10 and L2. After normalization, the peak stress values of the UIV and UIV+1 were located in T2 and L2. Similarly, the peak stress values of the annulus fibrosus at the upper adjacent level were on T10 and L2 after normalization. However, the peak stress values of the interspinal/supraspinal complex forces were concentrated on T11, T12, and L1 after normalization whilst the peak stress value of the pedicle screw was on T2. Controversy remains over the fusion of T10, and this study simulated testing conditions with gravitational loading only. However, further assessment is needed prior to reaching definitive conclusions.

Biomechanical compatibility of osteoporotic vertebral augmentation with cancellous bone granules and bone cement: a finite element evaluation / 医用生物力学

Objective The goal of this study was to investigate the biomechanical compatibility effects of cancellous bone granule(CBG) augmentation of Optimesh and polymethylmethacrylate (PMMA) augmentation of Kyphoplasty on treated andadjacent non-treated vertebral bodies. Methods Three-dimensional, anatomically detailed finite element (FE) models of the L1–L2functional spinal unit (FSU) were developed on the basis of cadaver computed tomography (CT) scans. The material properties and plug forms of the L2 centrum were adapted to simulate osteoporosis, CBG and PMMA augmentation. The models assumed a three-column loading configuration as the following types: compression, flexion and extension. Results Compared with the osteoporotic model, changes in stress and strain at adjacent levels both of CBG and PMMA augmentation models were minimal, but stresses/strains within the two reinforcement material plugs were modified distinctly and differently. In addition, osteoporosis, CBG and PMMA augmentation had little effect on either the axial compressive displacement of the three columns or the average disc internal pressure in all models. Conclusion Both morcelized cancellous bone and PMMA augmentation restore the total strength and stiffness level of treated vertebral bodies and benefit the reconstruction of vertebral function. Regarding the biomechanical compatibility and the biocompatibility of the treated vertebral body and reinforcement material, however, the morcelized cancellous bone is better than PMMA augmentation.