Biomechanical evaluation of predictive parameters of progression in adolescent isthmic spondylolisthesis: a computer modeling and simulation study

Biomechanical significance of intervertebral discs on growthplate stresses in scoliotic trunks following unilateral muscle weakening: A hybrid approach of finite element and musculoskeletal modeling

This study aimed to ascertain the relevance of intervertebral discs (IVD) in the stress distribution on growthplates (GPs) of a trunk model with adolescent idiopathic scoliosis (AIS) following a unilateral weakening of muscles. A thoracolumbar spine finite element (FE) model of a young female healthy and an AIS spine comprising GPs linked to the T12 through sacrum vertebrae. Two scenarios of including (FEI) and excluding (FEE) IVDs were considered. Then, using optimization-driven musculoskeletal models of the AIS and healthy trunks, the FE models were examined under subject-specific muscle forces and gravity loads. Results of this study demonstrate that when IVDs included in the FE model, an increase, ranging from 0.2 to 1.7 MPa, with the highest value occurring at the apex of the AIS model, in the von Mises stresses in the GPs. The ratio of 1.5 was found for the maximum von-Mises stress value on the most tilted GP in the FEI over the FEE model. Unilateral paralysis of muscles caused a reduction of 50% and 63% in the von Mises stress ratio of the concave-over-convex side of the most tilted GP in the FEI and FEE models of the AIS spine with healthy muscles, respectively. The intradiscal pressures, found for FEE and FEI models, assented to recent in-vivo investigations. Nonetheless, employing IVDs in the simulations provides an indispensable tool to anticipate the effects of neuromuscular disorders on GP stresses in an AIS spine and predict deformity progression during growth.

Biomechanical assessment of anterior plate system, bilateral pedicle screw and transdiscal screw system for high-grade spondylolisthesis: a finite element study

Introduction

Limited information regarding the biomechanical evaluation of various internal fixation techniques for high-grade L5-S1 spondylolisthesis is available. The stiffness of the operated segment and stress on the hardware can profoundly influence clinical outcomes and patient satisfaction. The objective of this study was to quantitatively investigate biomechanical profiles of various fusion methods used for high-grade spondylolisthesis by using finite element (FE) analysis.

Methods

An FE lumbar spine model of healthy spine was developed based on a patient's CT scan. High-grade (III-IV) spondylolisthesis (SP model) was created by sliding L5 anteriorly and modifying L5-S1 facet joints. Three treatment scenarios were created by adding various implants to the model. These scenarios included L5-S1 interbody cage in combination with three different fixation methods-the anterior plate system (APS), bilateral pedicle screw system (BPSS), and transdiscal screw system (TSS). Range of motion (ROM), von Mises stress on cage, internal fixation as well as on the adjacent annuli were obtained and compared. The resistance to slippage was investigated by applying shear force on L5 vertebra and measuring its displacement regarding to S1.

Results

Under different loading conditions all treatment scenarios showed substantial reduction of ROM in comparison with SP model. No notable differences in ROM were observed between treatment models. There was no notable difference in cage stress among models. The von Mises stress on the internal fixation in the TSS model was less than in APS and BPSS. The TSS model demonstrated superior resistance to shear load compared to APS and BPSS. No discernible difference was observed between the SP, APS, BPSS, and TSS models when compared the ROM for adjacent level L4-L5. TSS's von Mises stress of the adjacent annulus was higher than in APS and BPSS.

Conclusions

The TSS model exhibited biomechanical superiority over the APS and BPSS models.

A radiological parametric comparison of low-grade lytic spondylolisthesis to degenerative spondylolisthesis - A retrospective approach to establish its dysplastic origin

Objectives

This study aims to compare low-grade lytic spondylolisthesis (LS) and degenerative spondylolisthesis (DS) radiologically. In addition, it seeks to identify underlying similarities between LS and DS.

Methods

This study included patients with low-grade single-level spondylolisthesis at L4-L5 or L5-S1. They were categorized into LS and DS. Radiological features, including pedicle height, width, transverse, and sagittal angle, as well as anterior vertebral heights (AVH) and posterior vertebral heights (PVH), were measured using T1-weighted magnetic resonance imaging.

Results

The study involved 88 patients: 46 in the DS group and 42 in the LS group. In the LS group, the AVH was significantly higher than the posterior height at L4 and L5 (L4 PVH/AVH ratio 0.93 in LS vs. 0.96 in DS; L5 PVH/AVH ratio 0.84 in LS vs. 0.92 in DS), and pedicles were more medially oriented (L4: 19.62° in LS vs. 17.7° in DS; L5: 28.92° in LS vs. 26.47° in DS). In addition, at L5, the pedicle height (10.67 mm in LS vs. 11.48 mm in DS) and width (13.56 mm in LS vs. 14.37 mm in DS) were smaller compared to the DS group.

Conclusions

Low-grade LS shows distinct radiological vertebral and pedicle anatomy compared to DS. Short and thin pedicles and wedge-shaped vertebrae in LS resemble DS, indicating its dysplastic origin.

Management of low back pain accompanying sagittal plane pathologies in children: Spondylolysis/spondylolisthesis and Scheuermann's disease

Background

Low back pain in childhood was underappreciated for a long time, but recent studies report higher prevalences, up to 70%. Two of the common causes are spondylolyis/spondylolisthesis and Scheuermann's disease. These disorders are relevant in a way they both cause significant back pain, and may disrupt the sagittal spinal balance.

Purpose

To present the current evidence on the diagnosis, natural history and treatment of these disorders with a special focus on sagittal spinal alignment.

Methods

This study is conducted as a literature review.

Results and Conclusions

Spondylolysis and low-grade spondylolisthesis have a benign course and are typically treated conservatively. When pars repair is indicated, pedicle screw-based techniques achieve more than 90% fusion with acceptable complication rates. High-grade spondylolisthesis, however, is frequently progressive. Surgical treatment involves fusion, which can be done in situ or after reduction. Reduction is useful for "unbalanced" patients to acquire sagittal spinopelvic balance, and it is important to distinguish these patients. Despite lowering the risk for pseudoarthrosis, reduction brings a risk for neurologic complications. With re-operation rates as high as 40%, these patients definitely require careful preoperative planning. Scheuermann's disease generally causes back pain in addition to cosmetic discomfort during adolescence. If the kyphosis is lower than 60°, symptoms typically resolve into adulthood with conservative measures only. However, it must be kept in mind that these patients may experience problems with physical performance and have a lower quality of life even when the problem seems to have "resolved". Severe kyphosis and intractable back pain are the most frequently referred surgical indications, and surgery typically involves fusion. Proper utilization of osteotomies and proper selection of the upper and lower fusion levels are of utmost importance to prevent complications in these patients.

Analysis of the Spinopelvic Parameters in Patients with Fragility Fractures of the Pelvis

BACKGROUND

We investigated the spinopelvic parameters of lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT) and sacral slope (SS) in patients with fragility fractures of the pelvis (FFPs). We hypothesized that these parameters differ from asymptomatic patients.

METHODS

All patients treated for FFPs in a center of maximal care of the German Spine Society (DWG) between 2017 and 2021 were included. The inclusion criteria were age ≥ 60 years and the availability of a standing lateral radiograph of the spine and pelvis in which the spine from T12 to S1 and both femoral heads were visible. The baseline characteristics and study parameters were calculated and compared with databases of asymptomatic patients. The two-sample t-Test was performed with p < 0.05.

RESULTS

The study population (n = 57) consisted of 49 female patients. The mean age was 81.0 years. The mean LL was 47.9°, the mean PT was 29.4°, the mean SS was 34.2° and the mean PI was 64.4°. The mean value of LLI was 0.7. LL, LLI and SS were significantly reduced, and PI and PT were significantly increased compared to asymptomatic patients.

CONCLUSIONS

The spinopelvic parameters in patients with FFPs differ significantly from asymptomatic patients. In patients with FFPs, LL, LLI and SS are significantly reduced, and PI and PT are significantly increased. The sagittal spinopelvic balance is abnormal in patients with FFPs.

Is Sacral Dysmorphism Protective Against Spinopelvic Dissociation? Multicenter Case Series

OBJECTIVES

Investigate the incidence of sacral dysmorphism (SD) in patients with spinopelvic dissociation (SPD).

DESIGN

Retrospective case series.

SETTING

Two academic level 1 trauma centers.

PATIENTS/PARTICIPANTS

One thousand eight hundred fifty adult patients with sacral and pelvic fractures (OTA/AO 61-A, B, C).

INTERVENTION

Plain pelvic radiographs and CT scans.

MAIN OUTCOME MEASUREMENTS

Incidence of SD in patients with SPD. Secondary radiographic evaluation of fracture classification and deformity on sagittal imaging.

RESULTS

Eighty-two patients with SPD were identified, and 12.2% displayed features of SD, significantly less than reported in the literature. The S2 sacral body was the most common horizontal fracture location in patients with SD and nondysmorphic sacra (ND). Roy-Camille type I patterns were more common in ND (35%), versus type II in SD patients (40%). SD patients had lower body mass indexes (19.7 vs. 25.2, P = 0.001). Segmental kyphosis (22.5 degrees ND vs. 23.8 degrees SD, P = 0.838) and sacral kyphosis (26 degrees ND vs. 31 degrees SD, P = 0.605) were similar between groups. Percutaneous fixation was the most common surgical technique.

CONCLUSIONS

We report a significantly lower prevalence of SD in patients with SPD than previously reported in the literature. This suggests that variations in sacral osseous anatomy alter force transmission across the sacrum during traumatic loading, which may be protective against certain high-energy fracture patterns. Preoperative evaluation of sacral anatomy is critical, not only in determining the size and orientation of sacral segment safe zones for screw placement, but also to better understand the pathomechanics involved in sacral trauma.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Straighter low lumbar curvature in isthmic spondylolisthesis at L4

BACKGROUND

This study was conducted to compare differences in imaging features and clinical symptoms between patients with single-level isthmic spondylolisthesis (IS) at L4 and at L5 and to investigate the correlation between imaging and clinical parameters.

METHODS

This cross-sectional study evaluated patients with single-level IS who were enrolled between June 2011 and June 2018. A total of 139 patients, 44 in the L4 IS group and 95 in the L5 IS group, met the study criteria and were included. Imaging and clinical parameters obtained from the two groups were compared and analyzed.

RESULTS

Patients in the L4 IS group had smaller lower lumbar lordosis (LLL) (27.1 ± 8.2 vs. 30.9 ± 9.3, P = 0.021) and were of older age (58.5 ± 8.7 vs. 52.8 ± 10.1, P < 0.01) than those in the L5 IS group. As per the Roussouly classification system, most patients with L4 IS were classified as Type 2 (43.2%), whereas most patients with L5 IS fell under Type 3 (44.2%). In the L5 IS group, pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), and L5 incidence (L5I) were positively associated with slippage rate (SR), but the lumbosacral angle (LSA) was negatively associated with SR (P < 0.01). In the L4 IS group, only L5I showed a positive association with SR (P < 0.01). More significant associations were found among sagittal lumbo-pelvic parameters in the L5 IS group, but none were found between SR and Oswestry Disability Index (ODI) in either group.

CONCLUSIONS

When compared with patients with L5 IS, patients with L4 IS were of older age and had straighter low lumbar curvature when they were obviously symptomatic. PI was an important parameter for patients with L5 IS while for those with L4 IS, L5I deserved more attention for its significantly positive correlation with the degree of slippage.

The Joe-Lin Operative Classification System for Pediatric Lumbosacral Spondylolysis and Spondylolisthesis

OBJECTIVE

To propose and validate a novel and comprehensive classification of lumbosacral spondylolysis and spondylolisthesis in the pediatric population according to surgical managements.

METHODS

Cases of pediatric lumbosacral (L5/S1 level) spondylolysis and spondylolisthesis were reviewed. Lumbar Japanese Orthopedics Association score, health-related quality of life, spondylolisthesis, lumbosacral disc degeneration, and dysplastic features were included for evaluation of outcomes after surgery. We also conducted a reliability study to assess the classification.

RESULTS

A classification containing 4 types and a tentative treatment algorithm were proposed: type 1, direct pars repair without segmented fusion, for which the pedicle screw-U rod system is suitable; type 2, simple L5-S1 fusion; type 3, simple L4-S1 fusion; and type 4, simple L5-S2 fusion. All types of spondylolisthesis were suggested to achieve complete reduction and decompression. A total of 162 patients were included and we also reviewed the outcomes of patients in each type. All patients achieved satisfied outcomes. The reliability study showed that the average interobserver agreement was 89.5% (range, 85.2%-92.6%), with κ value of 0.862 (range, 0.802-0.901). Intraobserver agreement ranged from 88.9% to 92.6%, with an average κ value of 0.868 (range, 0.835-0.901).

CONCLUSIONS

In our study, we proposed and validated a novel comprehensive classification of pediatric lumbosacral spondylolysis and spondylolisthesis. The pedicle screw-U rod system provided more benefits in the treatment of simple lumbosacral spondylolysis, and fusion from L5 to S2 combined with S2 screw would also benefit patients with high-degree spondylolisthesis.

A mechanical analog thoracolumbar spine model for the evaluation of scoliosis bracing technology

Introduction

Thoracolumbar braces are used to treat Adolescent Idiopathic Scoliosis. The objective of this study was to design and validate a mechanical analog model of the spine to simulate a thoracolumbar, single-curve, scoliotic deformity in order to quantify brace structural properties and corrective force response on the spine.

Methods

The Scoliosis Analog Model used a linkage-based system to replicate 3D kinematics of spinal correction observed in the clinic. The Scoliosis Analog Model is used with a robotic testing platform and programmed to simulate Cobb angle and axial rotation correction while equipped with a brace. The 3D force and moment responses generated by the brace in reaction to the simulated deformity were measured by six-axis load cells.

Results

Validation of the model’s force transmission showed less than 6% loss in the force analysis due to assembly friction. During simulation of 10° Cobb angle and 5° axial rotation correction, the brace applied 101 N upwards and 67 N inwards to the apical connector of the model. Brace stiffness properties were 0.5–0.6 N/° (anteroposterior), 0.5–2.3 N/° (mediolateral), 23.3–26.5 N/° (superoinferior), and 0.6 Nm/° (axial rotational).

Conclusions

The Scoliosis Analog Model was developed to provide first time measures of the multidirectional forces applied to the spine by a thoracolumbar brace. This test assembly could be used as a future design and testing tool for scoliosis brace technology.

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 analysis of spino-pelvic postural configurations in spondylolysis subjected to various sport-related dynamic loading conditions

PURPOSE

To study the risks of spondylolysis due to extrinsic loading conditions related to sports activities and intrinsic spino-pelvic postural parameters [pelvic incidence (PI) and sacral slope (SS)].

METHODS

A comprehensive osseo-disco-ligamentous L4-S1 finite element model was built for three cases with spondylolysis representing three different spino-pelvic angular configurations (SS = 32°, 47°, 59° and PI = 49°, 58°, 72°, respectively). After simulating the standing posture, 16 dynamic loading conditions were computationally tested for each configuration by combining four sport-related loads (compression, sagittal and lateral bending and axial torque). For each simulation, the Von Mises stress, L5-S1 facet contact force and resultant internal loads at the sacral endplate were computed. Significant effects were determined with an ANOVA.

RESULTS

The maximal stress and volume of cancellous bone in the pars with stress higher than 75% of the ultimate stress were higher with 900 N simulated compression (2.2 MPa and 145 mm³) compared to only the body weight (1.36 MPa and 20.9 mm³) (p < 0.001). Combined compression with 10 Nm of flexion and an axial torque of 6 Nm generated the highest stress conditions (up to 2.7 MPa), and L5-S1 facet contact force (up to 430 N). The maximal stress was on average 17% higher for the case with the highest SS compared to the one with lowest SS for the 16 tested conditions (p = 0.0028).

CONCLUSIONS

Combined flexion and axial rotation with compression generated the highest stress conditions related to risks of spondylolysis. The stress conditions intensify in patients with higher PI and SS. These slides can be retrieved under Electronic Supplementary Material.

A Novel Nonlinear Parameter Estimation Method of Soft Tissues

The elastic parameters of soft tissues are important for medical diagnosis and virtual surgery simulation. In this study, we propose a novel nonlinear parameter estimation method for soft tissues. Firstly, an in-house data acquisition platform was used to obtain external forces and their corresponding deformation values. To provide highly precise data for estimating nonlinear parameters, the measured forces were corrected using the constructed weighted combination forecasting model based on a support vector machine (WCFM_SVM). Secondly, a tetrahedral finite element parameter estimation model was established to describe the physical characteristics of soft tissues, using the substitution parameters of Young's modulus and Poisson's ratio to avoid solving complicated nonlinear problems. To improve the robustness of our model and avoid poor local minima, the initial parameters solved by a linear finite element model were introduced into the parameter estimation model. Finally, a self-adapting Levenberg-Marquardt (LM) algorithm was presented, which is capable of adaptively adjusting iterative parameters to solve the established parameter estimation model. The maximum absolute error of our WCFM_SVM model was less than 0.03 Newton, resulting in more accurate forces in comparison with other correction models tested. The maximum absolute error between the calculated and measured nodal displacements was less than 1.5 mm, demonstrating that our nonlinear parameters are precise.

The Relationship Between Sacral Slope and Symptomatic Isthmic Spondylolysis in a Cohort of High School Athletes: A Retrospective Analysis

BACKGROUND

Spondylolysis with and without anterolisthesis is the most common cause of structural back pain in children and adolescents, but few predictive factors have been confirmed. An association between abnormal sacropelvic orientation and both spondylolysis and spondylolisthesis has been supported in the literature. Sacral slope and other sacropelvic measurements are easily accessible variables that could aid clinicians in assessing active adolescents with low back pain, particularly when the diagnosis of spondylolysis is suspected.

OBJECTIVE

To examine the relationship between sacral slope and symptomatic spondylolysis in a cohort of active adolescents.

DESIGN

Case-control retrospective study.

SETTING

Academic outpatient physiatry practice.

PATIENTS

Seventy-four patients of primarily adolescent age (between 12 and 22 years old) with a chief complaint of low back pain and presence of lateral radiographs of the lumbar spine were enrolled. Cases (n = 37) were defined as subjects with evidence of spondylolysis on both radiograph and magnetic resonance imaging of the lumbar spine. Controls (n = 37) were defined as subjects without spondylolysis.

METHODS

Using a single sagittal radiograph, taken with the patient standing, a fellowship-trained interventional spine physiatrist measured the sacral slope of each subject (angle between the superior plate of S1 and a horizontal reference on sagittal imaging of the lumbosacral spine). Ages and genders were collected from medical records.

MAIN OUTCOME MEASUREMENTS

The primary outcome was mean sacral slope. Mean sacral slope of cases was compared with mean sacral slope of controls with the Student t-test.

RESULTS

Ages ranged from 12 to 22 for both groups, with no significant differences in age between the groups (cases: 16.8 ± 2.3 years; controls: 17.7 ± 2.7 years). The patients with spondylolysis (cases) consisted of 29 male and 8 female patients, whereas those without spondylolysis (controls) consisted of 15 male and 21 female patients (gender details for 1 patient were not available). The mean sacral slope among cases was 42.4°, whereas the mean sacral slope among controls was 37.4°. The difference achieved significance (P = .014).

CONCLUSIONS

The interdependence of positional parameters, such as sacral slope, with anatomic parameters, such as pelvic incidence, can affect lumbar lordosis and therefore upright positioning and loading of the spine. Sacral slope may be an important variable for clinicians to consider when caring for young athletes with low back pain, particularly when the index of suspicion for spondylolysis is high.

LEVEL OF EVIDENCE

IV.

Multilevel Thoracolumbar Spondylolysis with Spondylolisthesis at L4 on L5

A 24-year-old male patient was initially evaluated for persistent back pain. The visual analogue scale (VAS) score was 7 points. Physical examination revealed a decreased range of lumbar spinal motion, which caused pain. Simple X-ray revealed Meyerding grade 1 spondylolisthesis at L4 on L5, with mild dome-shaped superior endplate and consecutive multilevel spondylolysis at T12-L5. Standing anteroposterior and lateral views of the entire spine revealed normal balance of sagittal and coronal alignment. A computed tomography scan revealed bilateral spondylolysis at T12-L4, left unilateral spondylolysis at L5, and spina bifida at L5 to sacral region. Magnetic resonance imaging revealed mild dural ectasia at the lumbar region. Due to the absence of any neurological symptoms, the patient was managed conservatively. He was rested a few weeks with corset brace and physiotherapy. After treatment, his back pain improved, VAS score changed from 7 to 2, and he was able to return to normal activity.

Biomechanics of high-grade spondylolisthesis with and without reduction

The clinical advantages of reducing spondylolisthesis over fusion in situ have several intuitive reasons such as restore the spinal column into a more anatomic relationship and alignment. However, there is only little evidence in the literature supporting the theoretical advantages of reduction, and its effect on spinopelvic alignment remains poorly defined. In this study, a comprehensive finite element model was developed to analyze the biomechanics of the spine after spinal fusion at L5-S1 in both types of high-grade spondylolisthesis (balanced and unbalanced pelvis). The relevant clinical indices (i.e. spondylolisthesis grade and Dubousset lumbosacral angle), the displacement of L4-L5, pressure within the annulus and nucleus, and stress at L4-L5 were evaluated and compared. The model can well predict the changes of the important clinical indices during the surgery. For a balanced pelvis, the reduction has a minimal effect on the biomechanical conditions at the adjacent level during postsurgical activities. In the unbalanced case, reduction induced larger deformation in the lumbosacral region and a higher stress concentration at adjacent level. Whether such a stress concentration can lead to long-term disc degeneration is not known. The results provide additional information for the clinician considering reduction of high-grade spondylolisthesis.

Evidence-based support for S1 transpedicular screw entry point modification

BACKGROUND

In the literature, 'below and lateral to the superior S1 facet' is defined as the basic technique for screw introduction. Until a recently published modification, no analysis for alternative starting point has been proposed nor evaluated, although some surgeons claim to use some modifications. In this study, we analyse the data from anatomical and radiological studies for optimal starting point in transpedicular S1 screw placement.

METHODS

A Medline search for key word combination: sacrum, anatomy, pedicle, screws and bone density resulted in 26 publications relevant to the topic. After a review of literature, two articles were chosen, as those including the appropriate set of data. The data retrieved from the articles is used for the analysis. The spatial relation of S1 facet, pedicles and vertebral body with cortical thickness and bone density in normal, osteopenic and osteoporotic sacrum is analysed.

RESULTS

Presented data advocates for more medial placement of the screws due to higher bone density and lower bone loss in osteoporosis. Medial shift of the starting point does not increase the risk of spinal canal perforation. Osteoarthritic changes within the facet can augment the posterior supporting point for screw. The facet angular orientation is similar to convergent screw trajectory.

CONCLUSIONS

Modified technique for S1 screw placement takes advantage of latest anatomical and clinical data. In our opinion, technique modification improves the reproducibility and may increase stability and the screws within the posterior cortex of the S1 vertebra. Further biomechanical and clinical study should be performed to prove its superiority to classical technique.

Biomechanical loading of the sacrum in adolescent idiopathic scoliosis

BACKGROUND

The pelvis maintains an important role in transferring loads from the upper body to the lower extremities and hence contributes to the standing postural balance. Even though changes in spino-pelvic relative alignment are involved in the pathophysiology of scoliosis, the mechanism through which the transferred load between the spine and pelvis is related to the spinal deformity is not well understood.

METHODS

A personalized finite element model of the spine and pelvis was constructed for 11 right main thoracic and 23 left thoracolumbar/lumbar adolescent idiopathic scoliosis and 12 asymptomatic controls. The compressive stress distribution on the sacrum endplate was computed. The position of the stress distribution barycenter on the sacrum superior endplate in reference to the central hip vertical axis was projected on the transverse plane and compared between scoliotic subgroups and controls.

FINDINGS

The medio-lateral position of the stress distribution barycenter on the sacrum superior endplate was significantly different between the scoliotic subgroups and controls (p<0.05). The stress distribution barycenter on the sacrum superior endplate was located at the right side of the central hip vertical axis in 82% of the right main thoracic patients and to the left side of the central hip vertical axis in 91% of the left thoracolumbar/lumbar patients.

INTERPRETATION

Analysis of the transferred load to the sacrum provided insight into the biomechanical spino-pelvic interaction in 3D, showing that a thoracolumbar/lumbar scoliotic curve has an increased influence on sacral loads when compared to a main thoracic scoliotic curve.

The Use of Finite Element Models to Assist Understanding and Treatment For Scoliosis: A Review Paper

INTRODUCTION

Scoliosis is a complex spinal deformity whose etiology is still unknown, and its treatment presents many challenges. Finite element modeling (FEM) is one of the analytical techniques that has been used to elucidate the mechanism of scoliosis and the effects of various treatments.

METHODS

A literature review on the application of FEM in scoliosis evaluation and treatment has been undertaken. A literature search was performed in each of three major electronic databases (Google Scholar, Web of Science, and Ovid) using the key words "scoliosis" and "finite element methods/model". Articles using FEM and having a potential impact on clinical practice were included.

RESULTS

A total of 132 abstracts were retrieved. The query returned 105 articles in which the abstracts appeared to correspond to this review's focus, and 85 papers were retained. The current state of the art of FEM related to the biomechanical analysis of scoliosis is discussed in 4 sections: the etiology of adolescent idiopathic scoliosis, brace treatment, instrumentation treatment, and sensitivity studies of FEM. The limitations of FEM and suggested future work are also discussed.

Development of a detailed volumetric finite element model of the spine to simulate surgical correction of spinal deformities

A large spectrum of medical devices exists; it aims to correct deformities associated with spinal disorders. The development of a detailed volumetric finite element model of the osteoligamentous spine would serve as a valuable tool to assess, compare, and optimize spinal devices. Thus the purpose of the study was to develop and initiate validation of a detailed osteoligamentous finite element model of the spine with simulated correction from spinal instrumentation. A finite element of the spine from T1 to L5 was developed using properties and geometry from the published literature and patient data. Spinal instrumentation, consisting of segmental translation of a scoliotic spine, was emulated. Postoperative patient and relevant published data of intervertebral disc stress, screw/vertebra pullout forces, and spinal profiles was used to evaluate the models validity. Intervertebral disc and vertebral reaction stresses respected published in vivo, ex vivo, and in silico values. Screw/vertebra reaction forces agreed with accepted pullout threshold values. Cobb angle measurements of spinal deformity following simulated surgical instrumentation corroborated with patient data. This computational biomechanical analysis validated a detailed volumetric spine model. Future studies seek to exploit the model to explore the performance of corrective spinal devices.

Pelvic incidence and lumbar spine instability correlations in patients with chronic low back pain

Purpose

Many factors such as lumbar instability and spinopelvic alignment are associated with low back pain. Our purpose was to analyze the pelvic incidence - one of spinopelvic alignment parameters- and spine instability correlations in patients with chronic low back pain.

Methods

Fifty-two patients suffering from chronic low back pain entered this case control study. Lateral spine radiography was taken from patients. pelvic incidence and L3, L4 and L5‘s vertebral body width were measured for all patients, and lumbar instability was evaluated in 3 different levels: L5-S1, L4-L5 and L3-L4.

Results

Thirty-two patients having lumbar instability formed group A and 20 patients without lumbar spine instability allocated to group B. Average age, mean weight, height, body mass index and mean vertebral width of both groups did not differ meaningfully. Pelvic incidence‘s mean amounts set to 53.9 in group B and 57.7 in group A without any significant difference; but pelvic incidence was significantly lower in patients with lumbar instability of L5-S1 origin (P=0.01).

Conclusions

Overall, pelvic incidence did not differ between two groups. However, separate evaluation of each level revealed lumbar instability of L5-S1 segment to be associated with lower pelvic incidence.