Convergence analysis and validation of a discrete element model of the human lumbar spine

Degenerative diseases of the spine can lead to or hasten the onset of additional spinal problems that significantly reduce human mobility. The spine consists of vertebral bodies and intervertebral discs. The most degraded are intervertebral discs. The vertebral body consists of a shell (cortical bone tissue) and an internal content (cancellous bone tissue). The intervertebral disc is a complex structural element of the spine, consisting of the nucleus pulposus, annulus fibrosus, and cartilaginous plates. To develop numerical models for the vertebral body and intervertebral disc, first, it is necessary to verify and validate the models for the constituent elements of the lumbar spine. This paper, for the first time, presents discrete elements-based numerical models for the constituent parts of the lumbar spine, and their verification and validation. The models are validated using uniaxial compression experiments available in the literature. The model predictions are in good qualitative and quantitative agreement with the data of those experiments. The loading rate sensitivity analysis revealed that fluid-saturated porous materials are highly sensitive to loading rate: a 1000-fold increase in rate leads to the increase in effective stiffness of 130 % for the intervertebral disc, and a 250-fold increase in rate leads to the increase in effective stiffness of 50 % for the vertebral body. The developed model components can be used to create an L4-L5 segment model, which, in the future, will allow investigating the mechanical behavior of the spine under different types of loading.

Three-Dimensional Biomechanical Finite Element Analysis of Lumbar Disc Herniation in Middle Aged and Elderly

Lumbar intervertebral disc protrusion disease refers to the degeneration of intervertebral disc, rupture of fibrous ring, nucleus pulpous protrusion and stimulation or compression of nerve root. The import command in Mimics medical 3D reconstruction software was used to erase the irrelevant image data and obtain vertebral body images. The original 3D model of each vertebral body was built by 3D computing function. A three-dimensional finite element model was established to analyze the effect of different surgical methods on the mechanical distribution of the spine after disentomb. The stress distribution of the spine, intervertebral disc, and left and right articular cartilage at L4/L5 stage and the position shift of the fourth lumbar vertebra were analyzed under 7 working conditions of vertical, forward flexion, extension, left and right flexion, and left and right rotation. The results showed that the established model was effective, and the smaller the area of posterior laminar decompression was, the lesser the impact on spinal stability was. The PELD treatment of lumbar disc herniation had little impact on spinal biomechanics and could achieve good long-term biomechanical stability. Combining the clinical experiment method and finite element simulation, using the advantages of finite element software to optimize the design function can provide guidance for the design and improvement of medical devices and has important significance for the study of clinical mechanical properties and biomechanics.

Video-Assisted Thoracoscopy for Vertebral Body Tethering of Juvenile and Adolescent Idiopathic Scoliosis: Tips and Tricks of Surgical Multidisciplinary Management

VATS (video assisted thoracoscopic surgery) is routinely and successfully performed in minor and major complex thoracic procedures. This technique has been recently introduced for the treatment of severe forms of idiopathic scoliosis (IS) with the aim to repair the deformity, reduce morbidity and to prevent its progression in patients with skeletal immaturity. This study aims to present VATS in anterior vertebral body tethering (AVBT) approach to support the pediatric orthopedic surgeons during vertebral body fixation. Surgical and anesthesiologic tips and tricks are reported to assure a safe procedure. The study includes preadolescents with IS and a grade of scoliosis >40° that had a high probability of deterioration due to remaining growth (December 2018 to April 2021). Skeletal immaturity of enrolled patients was assessed by Sanders classification and Risser sign. Patients had a Risser score between 0 and 1 and a Sanders score >2 and <5. AVBT technique using VATS was performed by a senior pediatric surgeon assisting the pediatric orthopedic surgeon. Twenty-three patients have been submitted to VATS AVBT in the period of study (age range 9–14 years). The patients had a classified deformity Lenke 1A or B convex right and all types of curves were treated. In all patients, the vertebrae submitted to tethering surgery ranged from D5 to D12; mean curve correction was 43%. Three postoperative complications occurred: one late postoperative bleeding requiring a chest tube positioning on 12th postoperative day; one screw dislodged and needed to be removed; one child showed worsening of the scoliosis and needed a posterior arthrodesis. Initial results of VATS AVBT in growing patients with spinal deformities are encouraging. An appropriate selection of patients and a pediatric dedicated multidisciplinary surgical approach decrease intraoperative complications, time of operation and postoperative sequelae and guarantee an optimal outcome.

Anterior cervical corpectomy and fusion with stand-alone cages in patients with multilevel degenerative cervical spine disease is safe

Background In case of spinal cord compression behind the vertebral body, anterior cervical corpectomy and fusion (ACCF) proves to be a more feasible approach than cervical discectomy. The next step was the placement of an expandable titanium interbody in order to restore the vertebral height. The need for additional anterior plating with ACCF has been debatable and such technique has been evaluated by very few studies. The objective of the study is to evaluate radiographic and clinical outcomes in patients with multilevel degenerative cervical spine disease treated by stand-alone cages for anterior cervical corpectomy and fusion (ACCF). Methods Thirty-one patients (66.5 ± 9.75 years, range 53–85 years) were analyzed. Visual Analog Scale (VAS) and the 10-item Neck Disability Index (NDI) were assessed preoperatively and during follow-up on a regular basis after surgery and after one year at least. Assessment of radiographic fusion, subsidence, and lordosis measurement of Global cervical lordosis (GCL); fusion site lordosis (FSL); the anterior interbody space height (ant. DSH); the posterior interbody space height (post. DSH); the distance of the cage to the posterior wall of the vertebral body (CD) were done retrospectively. Mean clinical and radiographic follow-up was 20.0 ± 4.39 months. Results VAS-neck (p = 0.001) and VAS-arm (p < 0.001) improved from preoperatively to postoperatively. The NDI improved at the final follow-up (p < 0.001). Neither significant subsidence of the cages nor significant loss of lordotic correction were seen. All patients showed a radiographic union of the surgically addressed segments at the last follow up. Conclusions Application of a stand-alone expandable cage in the cervical spine after one or two-level ACCF without additional posterior fixation or anterior plating is a safe procedure that results in fusion. Neither significant subsidence of the cages nor significant loss of lordotic correction were seen. Trial registration Retrospectively registered. According to the Decision of the ethics committee, Jena on 25th of July 2018, that this study doesn’t need any registration. https://www.laek-thueringen.de/aerzte/ethikkommission/registrierung/.