Spine Model Research Articles

Intubation biomechanics: Computational modeling to identify methods to minimize cervical spine motion and spinal cord strain during laryngoscopy and tracheal intubation in an intact cervical spine

Study objectiveTo minimize the risk of cervical spinal cord injury in patients who have cervical spine pathology, minimizing cervical spine motion during laryngoscopy and tracheal intubation is commonly recommended. However, clinicians may better aim to reduce cervical spinal cord strain during airway management of their patients. The aim of this study was to predict laryngoscope force characteristics (location, magnitude, and direction) that would minimize cervical spine motions and cord strains. DesignWe utilized a computational model of the adult human cervical spine and spinal cord to predict intervertebral motions (rotation [flexion/extension] and translation [subluxation]) and cord strains (stretch and compression) during laryngoscopy. InterventionsRoutine direct (Macintosh) laryngoscopy conditions were defined by a specific force application location (mid-C3 vertebral body), magnitude (48.8 N), and direction (70 degrees). Sixty laryngoscope force conditions were simulated using 4 force locations (cephalad and caudad of routine), 5 magnitudes (25–200% of routine), and 3 directions (50, 70, 90 degrees). Main resultsUnder all conditions, extension at Oc-C1 and C1-C2 were greater than in all other cervical segments. Decreasing force magnitude to values reported for indirect laryngoscopes (8–17 N) decreased cervical extension to ~50% of routine values. The cervical cord was most likely to experience potentially injurious compressive strain at C3, but force magnitudes ≤50% of routine (≤24.4 N) decreased strain in C3 and all other cord regions to non-injurious values. Changing laryngoscope force locations and directions had minor effects on motion and strain. ConclusionsThe model predicts clinicians can most effectively minimize cervical spine motion and cord strain during laryngoscopy by decreasing laryngoscope force magnitude. Very low force magnitudes (<5 N, ~10% of routine) are necessary to decrease overall cervical extension to <50% of routine values. Force magnitudes ≤24.4 N (≤50% of routine) are predicted to help prevent potentially injurious compressive cord strain.

Region-Based Convolutional Neural Network-Based Spine Model Positioning of X-Ray Images.

Background Idiopathic scoliosis accounts for over 80% of all cases of scoliosis but has an unclear pathogenic mechanism. Many studies have introduced conventional image processing methods, but the results often fail to meet expectations. With the improvement and evolution of research in neural networks in the field of deep learning, many research efforts related to spinal reconstruction using the convolutional neural network (CNN) architecture of deep learning have shown promise. Purpose To investigate the use of CNN for spine modeling. Methods The primary technique used in this study involves Mask Region-based CNN (R-CNN) image segmentation and object detection methods as applied to spine model positioning of radiographs. The methods were evaluated based on common evaluation criteria for vertebral segmentation and object detection. Evaluations were performed using the loss function, mask loss function, classification loss function, target box loss function, average accuracy, and average recall. Results Many bony structures were directly identified in one step, including the lumbar spine (L1-L5) and thoracic spine (T1-T12) in frontal and lateral radiographs, thereby achieving initial positioning of the statistical spine model to provide spine model positioning for future reconstruction and classification prediction. An average detection box accuracy of 97.4% and an average segmentation accuracy of 96.8% were achieved for the prediction efficacy of frontal images, with good image visualization. Moreover, the results for lateral images were satisfactory considering the evaluation parameters and image visualization. Conclusion Mask R-CNN can be used for effective positioning in spine model studies for future reconstruction and classification prediction.

Biomechanical comparison of different interspinous process devices in the treatment of lumbar spinal stenosis: a finite element analysis

BackgroundLumbar spinal stenosis (LSS) is a common disease among elderly individuals, and surgery is an effective treatment. The development of minimally invasive surgical techniques, such as the lumbar interspinous process device (IPD), has provided patients with more surgical options.ObjectiveTo investigate the biomechanical properties of different IPDs, including BacFuse, X-Stop and Coflex, in the treatment of LSS.MethodsBased on the computed tomography images of a patient with LSS, four finite element (FE) models of L3-S5 were created in this study. The FE models included a surgical model of the intact lumbar spine and surgical models of the lumbar IPDs BacFuse, X-Stop, and Coflex. After validating the models, they were simulated for four physiological motions: flexion, extension, lateral bending and axial rotation, and range of motion (ROM). Stress distribution of discs and facet joints in each segment, stress distribution of the spinous process in the operated section, and stress distribution of the internal fixation were compared and analysed.ResultsCompared to the model of the intact lumbar spine, the other three models showed a decrease in ROM and disc and facet joint stresses in the surgical segment during movement and an increase in ROM and disc and facet joint stresses in the adjacent segments. These effects were greater for the proximal adjacent segment with BacFuse and more pronounced for the distal adjacent segment with Coflex, while X-Stop had the greatest stress effect on the spinous process in the surgical segment.ConclusionBacFuse, Coflex and X-Stop could all be implemented to effectively reduce extension and disc and facet joint stresses, but they also increase the ROM and disc and facet joint stresses in adjacent segments, which may cause degeneration.

Comanipulation Robotic Platform for Spine Surgery With Exteroceptive Visual Coupling: Development and Experimentation

Abstract In this paper, a novel surgical robotic platform intended to assist surgeons in cervical spine surgery is presented. The purpose of this surgery is to treat the cervical spine instabilities. The surgical procedure requires drilling into specific region of the vertebrae in order to attach spinal implants and thus ensure a normal spacing between each vertebra concerned. In this context, the proposed robotic platform allows to control and restrict the surgeon's movements to a specific drilling direction set by the surgeon. The current platform is composed of a collaborative robot with seven degrees-of-freedom (DoF) equipped with a drilling tool and directly comanipulated by the surgeon. A motion capture system, as an exteroceptive sensor device, provides the robot controller with the movement data of the vertebra to be drilled. Robot Operating System (ROS) framework is used to enable real-time communication between the collaborative robot and the visual exteroceptive device. In addition, an implemented compliance control program allows to enhance the safety aspect of the robotic platform. Indeed, the collaborative robot follows the patient's movements while constraining the tool movements to an optimal trajectory as well as a limited drilling depth selected by the surgeon. The collaborative robot's elbow movements are also restricted by exploiting the null-space in order to avoid collisions with other equipment or the medical team members. Experimental drilling trials have been performed by an orthopedic surgeon to validate the usefulness and different functionalities of the developed robotic platform, and provide that a collaborative robot can comply with a spine surgery procedure. These preliminary tests were performed in a lumbar spine model for which the use of a robotic device is most frequent due to a lower complexity compared to the cervical spine.

Biomechanical effect of posterior ligament repair in lamina repair surgery

Cervical laminectomy has usually been applied in treating cervical spinal cord tumour. However, spinal instability after laminectomy was observed with high occurrence rate, due to excising of posterior structures. This study was to investigate the biomechanical performances of ligament repair on the cervical stability in lamina repair surgery. A finite element of cervical spine model (C2-C7) was developed, and lamina repair surgery with and without ligament repair was simulated at C3-C6 segments. All models were loaded with pure moment of 1.5 Nm to produce flexion, extension, lateral blending and axial torsion. Compared to intact model, the range of motion (ROM) at C2-C3, C6-C7 increased by 12.8%-113.6% in lamina repair model (LRM), while the change of ROM in other segments was less than 9.2%. The change of ROM in all segments in the lamina and ligament repair model (LLRM) was less than 7.2%. The maximal intradiscal pressure (IDP) in adjacent segment (C2-C3 and C6-C7) increased by 73.7%, and the maximal stresses in capsular ligament increased by 168.6% in LRM model. By the other hand, the change of facet joint contact stress, IDP and stresses in capsular ligament in LLRM model were less than 11.5%. The differences of stresses on bone-screw interface and screw-plate system in C4,C5 between LRM and LLRM were less than 5.9 MPa (2.7%), but this value in C3 and C6 were up to 105.7 MPa (41.8%). Laminectomy without reconstruction of posterior ligament resulted larger mobility in the adjacent segments, which might induce spinal instability as postoperative complications. Repairing or preserving the posterior ligament in the lamina repair is benefit to spinal integrity and stability.

Novel force–displacement control passive finite element models of the spine to simulate intact and pathological conditions; comparisons with traditional passive and detailed musculoskeletal models

Passive finite element (FE) models of the spine are commonly used to simulate intact and various pre- and postoperative pathological conditions. Being devoid of muscles, these traditional models are driven by simplistic loading scenarios, e.g., a constant moment and compressive follower load (FL) that do not properly mimic the complex in vivo loading condition under muscle exertions. We aim to develop novel passive FE models that are driven by more realistic yet simple loading scenarios, i.e., in vivo vertebral rotations and pathological-condition dependent FLs (estimated based on detailed musculoskeletal finite element (MS-FE) models). In these novel force–displacement control FE models, unlike the traditional passive FE models, FLs vary not only at different spine segments (T12-S1) but between intact, pre- and postoperative conditions. Intact, preoperative degenerated, and postoperative fused conditions at the L4-L5 segment for five static in vivo activities in upright and flexed postures were simulated by the traditional passive FE, novel force–displacement control FE, and gold-standard detailed MS-FE spine models. Our findings indicate that, when compared to the MS-FE models, the force–displacement control passive FE models could accurately predict the magnitude of disc compression force, intradiscal pressure, annulus maximal von Mises stress, and vector sum of all ligament forces at adjacent segments (L3-L4 and L5-S1) but failed to predict disc shear and facet joint forces. In this regard, the force–displacement control passive FE models were much more accurate than the traditional passive FE models. Clinical recommendations made based on traditional passive FE models should, therefore, be interpreted with caution.

Biomechanical analysis of the impact of increasing levels of body mass index on the ability of a bracing orthosis to alter the asymmetric compressive growth plate loading in a scoliotic spine

BackgroundThe impact of increasing body mass index (BMI) on the magnitude of alterations in the asymmetric compressive vertebral growth plate loading of a scoliotic spine following 50% in-brace correction is studied using the finite element method, and subsequent alteration of the longitudinal bone growth rate is quantified. MethodsUpper body weight loading corresponding to a single patient spine geometry representing 4 BMI classifications – overweight (BMI = 25 kg/m2), and class-1, -2, and -3 obesity (BMI – 30 kg/m2, 35 kg/m2, and 40 kg/m2, respectively) – is applied to a three-dimensional finite element model (FEM) of the human thoracolumbosacral spine. The FEM represents a Lenke 1AN scoliotic curve type with 30-degree Cobb angle and 10-degree apical vertebral rotation. Bracing simulation is performed until 50% in-brace correction is achieved. Changes in bending moment at each motion segment and on each growth plate after bracing is simulated and compared between each BMI level. FindingsAs BMI increases, the average magnitude of change in bending moment on each growth plate following bracing decreases. For BMIs 30 kg/m2, 35 kg/m2, and 40 kg/m2, the average change in bending moment on each vertebral growth plate following 50% in-brace correction is 31% smaller (P = .00006), 60% smaller (P = .00007), and 96% smaller (P = .00006), respectively, than for BMI 25 kg/m2. InterpretationsResults indicate that BMI significantly impacts the ability of a bracing orthosis to alter the asymmetric compressive growth plate loading in a scoliotic spine, which is the design function of bracing. This suggests that increasing BMI may significantly impact the ability of a bracing orthosis to halt curve progression in a scoliotic patient.

Development and evaluation of a numerical spine model comprising intra-abdominal pressure for use in assessing physiological changes on abdominal compliance and spinal stability

BackgroundAbdominal compliance is the “measure of ease of abdominal expansion” and determines whether a patient can withstand high intra-abdominal pressures. Thus, high compliance indicates that the abdomen can expand relatively freely, while low compliance restricts abdominal expansion. The global objective of the present work is to evaluate the effect of physiological changes on abdominal compliance using a comprehensive spine finite element model inclusive of intra-abdominal pressure. MethodsThe effect of changing Young's modulus, abdominal wall thickness, and abdominal radii on abdominal compliance were evaluated. Intra-abdominal pressure and thoracolumbar fascia forces were also evaluated to assess abdominal physiological changes effects on overall static spinal stability. FindingsResults showed that as wall thickness increased, compliance decreased. Similar findings were made with an increase in abdominal radius and Young's modulus. Furthermore, the active reduction in compliance, caused by increased elasticity and abdominal radius, resulted in an increase in spinal supportive forces originating from the thoracolumbar fascia and intra-abdominal pressurization, along with an increase in spine displacement from its original stable position. There was no clear stability trend for the case of changing abdominal wall thickness as fluctuations were present. InterpretationInvestigated mechanics and data trends suggested that dangerously low compliance levels might result from poor abdominal elasticity and thickening fat layers. This led to a direct discussion and recommendations for obesity conditions and laparoscopy applications. Lastly, static spinal stability showed to improve through increasing active abdominal compliance by means of actively engaging abdominal pressure, hence augmenting abdominal active elasticity.

Biomechanical Evaluation of Osteoporotic Spine Models Treated with Balloon Kyphoplasty (BKP) Procedure

Biomechanical Evaluation of Osteoporotic Spine Models Treated with Balloon Kyphoplasty (BKP) Procedure

Biomechanical Properties of Paraspinal Muscles Influence Spinal Loading-A Musculoskeletal Simulation Study.

Paraspinal muscles are vital to the functioning of the spine. Changes in muscle physiological cross-sectional area significantly affect spinal loading, but the importance of other muscle biomechanical properties remains unclear. This study explored the changes in spinal loading due to variation in five muscle biomechanical properties: passive stiffness, slack sarcomere length (SSL), in situ sarcomere length, specific tension, and pennation angle. An enhanced version of a musculoskeletal simulation model of the thoracolumbar spine with 210 muscle fascicles was used for this study and its predictions were validated for several tasks and multiple postures. Ranges of physiologically realistic values were selected for all five muscle parameters and their influence on L4-L5 intradiscal pressure (IDP) was investigated in standing and 36° flexion. We observed large changes in IDP due to changes in passive stiffness, SSL, in situ sarcomere length, and specific tension, often with interesting interplays between the parameters. For example, for upright standing, a change in stiffness value from one tenth to 10 times the baseline value increased the IDP only by 91% for the baseline model but by 945% when SSL was 0.4 μm shorter. Shorter SSL values and higher stiffnesses led to the largest increases in IDP. More changes were evident in flexion, as sarcomere lengths were longer in that posture and thus the passive curve is more influential. Our results highlight the importance of the muscle force-length curve and the parameters associated with it and motivate further experimental studies on in vivo measurement of those properties.

Porous interbody fusion cage design via topology optimization and biomechanical performance analysis

The porous interbody fusion cage could provide space and stable mechanical conditions for postoperative intervertebral bone ingrowth. It is considered to be an important implant in anterior cervical discectomy and internal fixation. In this study, two types of unit cells were designed using topology optimization method and introduced to the interbody fusion cage to improve the biomechanical performances of the cage. Topology optimization under two typically loading conditions was first conducted to obtain two unit cells (O-unit cell and D-unit cell) with the same volume fraction. Porous structures were developed by stacking the obtained unit cells in space, respectively. Then, porous interbody fusion cages were obtained by the Boolean intersection between the global structural layout and the porous structures. Finite element models of cervical spine were created that C5-C6 segment was fused by the designed porous cages. The range of motion (ROM) of the cervical spine, the maximum stress on the cage and the bone graft, and the stress and displacement distributions of the cage were analyzed. The results showed the ROMs of C5-C6 segment in D-unit cell and O-unit cell models were range from 0.14° to 0.25° under different loading conditions; the cage composed of the D-unit cells had a more uniform stress distribution, smaller displacement on cage, a more reasonable internal stress transfer mode (transmission along struts of the unit cell), and higher stress on the internal bone graft (0.617 MPa). In conclusion, the optimized porous cage is a promising candidate for fusion surgery, which would avoid the cage subsidence, and promote the fusion of adjacent endplates.

Biomechanical analysis of stand-alone lumbar interbody cages versus 360° constructs: an in vitro and finite element investigation.

Low fusion rates and cage subsidence are limitations of lumbar fixation with stand-alone interbody cages. Various approaches to interbody cage placement exist, yet the need for supplemental posterior fixation is not clear from clinical studies. Therefore, as prospective clinical studies are lacking, a comparison of segmental kinematics, cage properties, and load sharing on vertebral endplates is needed. This laboratory investigation evaluates the mechanical stability and biomechanical properties of various interbody fixation techniques by performing cadaveric and finite element (FE) modeling studies. An in vitro experiment using 7 fresh-frozen human cadavers was designed to test intact spines with 1) stand-alone lateral interbody cage constructs (lateral interbody fusion, LIF) and 2) LIF supplemented with posterior pedicle screw-rod fixation (360° constructs). FE and kinematic data were used to validate a ligamentous FE model of the lumbopelvic spine. The validated model was then used to evaluate the stability of stand-alone LIF, transforaminal lumbar interbody fusion (TLIF), and anterior lumbar interbody fusion (ALIF) cages with and without supplemental posterior fixation at the L4-5 level. The FE models of intact and instrumented cases were subjected to a 400-N compressive preload followed by an 8-Nm bending moment to simulate physiological flexion, extension, bending, and axial rotation. Segmental kinematics and load sharing at the inferior endplate were compared. The FE kinematic predictions were consistent with cadaveric data. The range of motion (ROM) in LIF was significantly lower than intact spines for both stand-alone and 360° constructs. The calculated reduction in motion with respect to intact spines for stand-alone constructs ranged from 43% to 66% for TLIF, 67%-82% for LIF, and 69%-86% for ALIF in flexion, extension, lateral bending, and axial rotation. In flexion and extension, the maximum reduction in motion was 70% for ALIF versus 81% in LIF for stand-alone cases. When supplemented with posterior fixation, the corresponding reduction in ROM was 76%-87% for TLIF, 86%-91% for LIF, and 90%-92% for ALIF. The addition of posterior instrumentation resulted in a significant reduction in peak stress at the superior endplate of the inferior segment in all scenarios. Stand-alone ALIF and LIF cages are most effective in providing stability in lateral bending and axial rotation and less so in flexion and extension. Supplemental posterior instrumentation improves stability for all interbody techniques. Comparative clinical data are needed to further define the indications for stand-alone cages in lumbar fusion surgery.

Adjacent segments biomechanics following lumbar fusion surgery: a musculoskeletal finite element model study.

This study exploits a novel musculoskeletal finite element (MS-FE) spine model to evaluate the post-fusion (L4-L5) alterations in adjacent segment kinetics. Unlike the existing MS models with idealized representation of spinal joints, this model predicts stress/strain distributions in all passive tissues while organically coupled to a MS model. This generic (in terms of musculature and material properties) model uses population-based in vivo vertebral sagittal rotations, gravity loads, and an optimization algorithm to calculate muscle forces. Simulations represent individuals with an intact L4-L5, a preoperative severely degenerated L4-L5 (by reducing the disc height by ~ 60% and removing the nucleus incompressibility), and a postoperative fused L4-L5 segment with either a fixed or an altered lumbopelvic rhythm with respect to the intact condition (based on clinical observations). Changes in spine kinematics and back muscle cross-sectional areas (due to intraoperative injuries) are considered based on in vivo data while simulating three activities in upright/flexed postures. Postoperative changes in some adjacent segment kinetics were found considerable (i.e., larger than 25%) that depended on the postoperative lumbopelvic kinematics and preoperative L4-L5 disc condition. Postoperative alterations in adjacent disc shear, facet/ligament forces, and annulus stresses/strains were greater (> 25%) than those found in intradiscal pressure and compression (< 25%). Kinetics of the lower (L5-S1) and upper (L3-L4) adjacent segments were altered to different degrees. Alterations in segmental rotations mainly affected adjacent disc shear forces, facet/ligament forces, and annulus/collagen fibers stresses/strains. An altered lumbopelvic rhythm (increased pelvis rotation) tends to mitigate some of these surgically induced changes.

Bone Remodeling Around Solid and Porous Interbody Cages in the Lumbar Spine.

Spinal fusion is an effective surgical treatment for intervertebral disk degeneration. However, the consequences of implantation with interbody cages on load transfer and bone remodeling in the vertebral bodies have scarcely been investigated. Using detailed three-dimensional models of an intact and implanted lumbar spine and the strain energy density based bone remodeling algorithm, this study aimed to investigate the evolutionary changes in distribution of bone density (ρ) around porous and solid interbody cages. Follower load technique and submodeling approach were employed to simulate applied loading conditions on the lumbar spine models. The study determined the relationship between mechanical properties and parametrical characteristics of porous body-centered-cubic (BCC) models, which corroborated well with Gibson-Ashby and exponential regression models. Variations in porosity affected the peri-prosthetic stress distributions and bone remodeling around the cages. In comparison to the solid cage, stresses and strains in the cancellous bone decreased with an increase in cage porosity; whereas the range of motion increased. For the solid cage, increase in bone density of 20-28% was predicted in the L4 inferior and L5 superior regions; whereas the model with 78% porosity exhibited a small 3-5% change in bone density. An overall increase of 9-14% bone density was predicted in the L4 and L5 vertebrae after remodeling for solid interbody cages, which may influence disk degeneration in the adjacent segment. In comparison to the solid cage, an interbody cage with 65-78% porosity could be a viable and promising alternative, provided sufficient mechanical strength is offered.

Formulation and exploration of novel, intramuscular pressure based, muscle activation strategies in a spine model

Optimization models are often devised to assess spinal stability via estimating individual muscle forces. However, neglecting muscles' fluidic behavior remains an approximation due to the role of muscle pressure in force transmission. The purpose of this study was to leverage a validated Finite Element (FE) model of the spine, inclusive of Intra-Muscular Pressure (IMP), to explore muscle activation strategies towards maintaining equilibrium spinal stability. Three conventional strategies governing minimizing muscle effort, minimizing IVD compressive forces, and maintaining stability at all costs were first investigated to explore model's validity. Thereafter, two novel IMP-based strategies were devised and explored, specifically minimizing and maximizing IMP. The model was previously shown valid in light of in vivo and in silico observations with an average discrepancy of 6%. This being the case, the conventional strategies dictated efficacy in muscular activations whilst maintaining an equilibrium stable position, as quantified in the present paper, with a difference of 9.8% from documented data. In addition, the explored novel IMP-based strategies suggested the presence of a threshold individual muscles IMP, approximately 272 mmHg for the longissimus muscle for example, beyond which muscles potentially start to share radial loads with surrounding tissues, whilst limiting the contraction of the underlying muscles. In conclusion, this study theoretically supports the possibility of activation strategies based on muscular pressure, which the developed, verified, and validated FE spine model was leveraged to investigate. The explored novel IMP-based strategies may have significance in informing clinical applications such as motion analysis and functional electrical stimulation of muscles.

Finite element study of the impact of pedicle screw density on the biomechanical response of a Lenke 1AN scoliotic curve

IntroductionBenefits of increasing screw density in posterior instrumentation used to treat a scoliotic deformity are demonstrated using a three-dimensional finite element model (FEM) of the thoracolumbosacral spine. MethodsThe FEM represents a Lenke 1AN scoliotic deformity with a 50° Cobb angle and 20° apical vertebral rotation. The curve is corrected with bilateral pedicle screw fixation and 75 separate randomized screw distributions. ResultsTotal construct screw density, concave rod screw locations at T6, T10, T11 and T12, and convex rod screw locations at T7 and T12 each correlate strongly with reductions in postoperative Cobb angle (P < 0.05). Apical vertebral rotation is greatly impacted (reduced) by screws placed at the apical vertebra on both concave and convex rods (P < 0.05). Under pure moment loading, intersegmental micromotion is generally reduced when motion segment screw density is increased, with the exception being the upper instrumented joint. ConclusionsThese results suggest that increasing the screw density of posterior constructs used to treat a Lenke 1AN scoliotic deformity may improve the de-rotation correction with better postural restoration, reducing the risk of future complications including pseudarthrosis.

Patient‐Specific Self‐Powered Metamaterial Implants for Detecting Bone Healing Progress

AbstractThere is an unmet need for developing a new class of smart medical implants with novel properties and advanced functionalities. Here, the concept of “self‐aware implants” is proposed to enable the creation of a new generation of multifunctional metamaterial implantable devices capable of responding to their environment, empowering themselves, and self‐monitoring their condition. These functionalities are achieved via integrating nano energy harvesting and mechanical metamaterial design paradigms. Various aspects of the proposed concept are highlighted by developing proof‐of‐concept interbody spinal fusion cage implants with self‐sensing, self‐powering, and mechanical tunability features. Bench‐top testing is performed using synthetic biomimetic and human cadaver spine models to evaluate the electrical and mechanical performance of the developed patient‐specific metamaterial implants. The results show that the self‐aware cage implants can diagnose bone healing process using the voltage signals generated internally through their built‐in contact‐electrification mechanisms. The voltage and current generated by the implants under the axial compression forces of the spine models reach 9.2 V and 4.9 nA, respectively. The metamaterial implants can serve as triboelectric nanogenerators to empower low‐power electronics. The capacity of the proposed technology to revolutionize the landscape of implantable devices and to achieve better surgical outcomes is further discussed.

Biomechanical study of oblique lumbar interbody fusion (OLIF) augmented with different types of instrumentation: a finite element analysis

BackgroundTo explore the biomechanical differences in oblique lumbar interbody fusion (OLIF) augmented by different types of instrumentation.MethodsA three-dimensional nonlinear finite element (FE) model of an intact L3-S1 lumbar spine was built and validated. The intact model was modified to develop five OLIF surgery models (Stand-alone OLIF; OLIF with lateral plate fixation [OLIF + LPF]; OLIF with unilateral pedicle screws fixation [OLIF + UPSF]; OLIF with bilateral pedicle screws fixation [OLIF + BPSF]; OLIF with translaminar facet joint fixation + unilateral pedicle screws fixation [OLIF + TFJF + UPSF]) in which the surgical segment was L4–L5. Under a follower load of 500 N, a 7.5-Nm moment was applied to all lumbar spine models to calculate the range of motion (ROM), equivalent stress peak of fixation instruments (ESPFI), equivalent stress peak of cage (ESPC), equivalent stress peak of cortical endplate (ESPCE), and equivalent stress average value of cancellous bone (ESAVCB).ResultsCompared with the intact model, the ROM of the L4–L5 segment in each OLIF surgery model decreased by > 80%. The ROM values of adjacent segments were not significantly different. The ESPFI, ESPC, and ESPCE values of the OLIF + BPSF model were smaller than those of the other OLIF surgery models. The ESAVCB value of the normal lumbar model was less than the ESAVCB values of all OLIF surgical models. In most postures, the ESPFI, ESPCE, and ESAVCB values of the OLIF + LPF model were the largest. The ESPC was higher in the Stand-alone OLIF model than in the other OLIF models. The stresses of several important components of the OLIF + UPSF and OLIF + TFJF + UPSF models were between those of the OLIF + LPF and OLIF + BPSF models.ConclusionsOur biomechanical FE analysis indicated the greater ability of OLIF + BPSF to retain lumbar stability, resist cage subsidence, and maintain disc height. Therefore, in the augmentation of OLIF, bilateral pedicle screws fixation may be the best approach.

Numerical investigation on the stability of human upper cervical spine (C1–C3)

The finite element method (FEM) is an efficient and powerful tool for studying human spine biomechanics. In this study, a detailed asymmetric three-dimensional (3D) finite element (FE) model of the upper cervical spine was developed from the computed tomography (CT) scan data to analyze the effect of ligaments and facet joints on the stability of the upper cervical spine. A 3D FE model was validated against data obtained from previously published works, which were performed in vitro and FE analysis of vertebrae under three types of loads, i.e. flexion/extension, axial rotation, and lateral bending. The results show that the range of motion of segment C1-C2 is more flexible than that of segment C2-C3. Moreover, the results from the FE model were used to compute stresses on the ligaments and facet joints of the upper cervical spine during physiological moments. The anterior longitudinal ligaments (ALL) and interspinous ligaments (ISL) are found to be the most active ligaments, and the maximum stress distribution is appear on the vertebra C3 superior facet surface under both extension and flexion moments.

Soft Tissue Injury in Cervical Spine Is a Risk Factor for Intersegmental Instability: A Finite Element Analysis

Soft tissue cervical spine injury (CSI) has the possibility of causing cervical segmental instability, which can lead to spinal cord injury. There is a lack of certainty in assessing whether soft tissue CSI is unstable or not. This biomechanical study aimed to investigate the risk factors of soft tissue CSI. A 3-dimensional finite element model of the ligamentous cervical spine (C2-C7) was created from medical images. Three soft tissue injury models were simulated at C4-C5: 1) posterior ligament complex (PLC) injury, 2) intervertebral disk (ID) with anterior longitudinal ligament injury (IDI), and 3) anterior longitudinal ligament, PLC, and ID injury (API) model. Pure moment with compressive follower load was applied, and the range of motion, annular stress, nucleus stress, and facet forces were analyzed. For the IDI and API models, the range of motion increased at the injury level in extension (by 101%) and left/right axial rotations (>30%) compared with the intact model. The IDI and API models showed an increase of >50% in annular and nucleus stresses at the injury level in extension and left/right rotations compared with the intact model. The PLC injury showed similar stresses as the intact model except for flexion. The facet contact forces of IDI and API models increased more than 100% compared with other models in all motions. In CSI, all soft tissues have a key role in stabilizing cervical spine, but ID is the most important component of all.