Intervertebral Rotation Research Articles

Inter-Specimen Analysis of Diverse Finite Element Models of the Lumbar Spine.

Over the past few decades, there has been a growing popularity in utilizing finite element analysis to study the spine. However, most current studies tend to use one specimen for their models. This research aimed to validate multiple finite element models by comparing them with data from in vivo experiments and other existing finite element studies. Additionally, this study sought to analyze the data based on the gender and age of the specimens. For this study, eight lumbar spine (L2-L5) finite element models were developed. These models were then subjected to finite element analysis to simulate the six fundamental motions. CT scans were obtained from a total of eight individuals, four males and four females, ranging in age from forty-four (44) to seventy-three (73) years old. The CT scans were preprocessed and used to construct finite element models that accurately emulated the motions of flexion, extension, lateral bending, and axial rotation. Preloads and moments were applied to the models to replicate physiological loading conditions. This study focused on analyzing various parameters such as vertebral rotation, facet forces, and intradiscal pressure in all loading directions. The obtained data were then compared with the results of other finite element analyses and in vivo experimental measurements found in the existing literature to ensure their validity. This study successfully validated the intervertebral rotation, intradiscal pressure, and facet force results by comparing them with previous research findings. Notably, this study concluded that gender did not have a significant impact on the results. However, the results did highlight the importance of age as a critical variable when modeling the lumbar spine.

Numerical investigation of intra-abdominal pressure and spinal load-sharing upon the application of an abdominal belt

Chronic low back pain patients may experience spinal instability. Abdominal belts (ABs) have been shown to improve spine stability, trunk stiffness, and resiliency to spinal perturbations. However, research on the contributing mechanisms is inconclusive. ABs may increase intra-abdominal pressure (IAP) and reduce paraspinal soft tissue contribution to spine stability without increasing spinal compressive loads. A finite element model (FEM) of the spine inclusive of the T1-S1 vertebrae, intervertebral discs (IVDs), ribcage, pelvis, soft tissues, and abdominal cavity, without active muscle forces was developed. An identical FEM with an AB was developed. Both FEMs underwent trunk flexion. Following validation, the models’ intervertebral rotation (IVR), IAP, IVD pressure, and tensile stress in the multifidus (MF), erector spinae (ES), and thoracolumbar fascia (TLF) were compared. The inclusion of an AB resulted in a 3.8 kPa IAP increase, but a decreased average soft tissue tensile stress of 0.28 kPa. The TLF withstood the majority of tension being transferred across the paraspinal soft tissues (>70 %). The average IVR in the AB model decreased by 10 %, with the lumbar spine experiencing the largest reduction. The lumbar IVDs of the AB model likewise showed a 31 % reduction in average IVD pressure. Using an AB improved trunk bending stiffness, primarily in the lumbar spine. Wearing an AB had minimal effect on reducing tensile stress in theES. The skewed stress distribution towards the TLF suggests its large contribution to spine stability and the potential advantage in unloading the structure when wearing an AB, measured herein at8 %.

Development and validation of lumbar spine finite element model.

The functional biomechanics of the lumbar spine have been better understood by finite element method (FEM) simulations. However, there are still areas where the behavior of soft tissues can be better modeled or described in a different way. The purpose of this research is to develop and validate a lumbar spine section intended for biomechanical research. A FE model of the 50th percentile adult male (AM) Total Human Model for Safety (THUMS) v6.1 was used to implement the modifications. The main modifications were to apply orthotropic material properties and nonlinear stress-strain behavior for ligaments, hyperelastic material properties for annulus fibrosus and nucleus pulposus, and the specific content of collagenous fibers in the annulus fibrosus ground substance. Additionally, a separation of the nucleus pulposus from surrounding bones and tissues was implemented. The FE model was subjected to different loading modes, in which intervertebral rotations and disc pressures were calculated. Loading modes contained different forces and moments acting on the lumbar section: axial forces (compression and tension), shear forces, pure moments, and combined loading modes of axial forces and pure moments. The obtained ranges of motion from the modified numerical model agreed with experimental data for all loading modes. Moreover, intradiscal pressure validation for the modified model presented a good agreement with the data available from the literature. This study demonstrated the modifications of the THUMS v6.1 model and validated the obtained numerical results with existing literature in the sub-injurious range. By applying the proposed changes, it is possible to better model the behavior of the human lumbar section under various loads and moments.

Correcting intervertebral rotation and scoliosis simultaneously by oblique lumbar interbody fusion: a 3D analysis of EOS images.

With advancements in minimally invasive techniques, oblique lumbar interbody fusion (OLIF) has gained widespread acceptance and is now commonly performed for adult degenerative scoliosis (ADS). The objective of this research paper is to evaluate three-dimensional (3D) intervertebral motions in EOS models before and after surgery and subsequently assess the efficacy of the 3D correction achieved through staged OLIF. In this retrospective study, 29 consecutive patients diagnosed with ADS were included, with a mean age of 63.6 years, who underwent staged OLIF surgery between 2018 and 2021. Spinopelvic parameters were assessed using EOS images, and 3D models were reconstructed to measure intervertebral motion angles (IMAs) in 70 surgical intervertebral segments, comprising wedge, lordosis, and axial rotation angles. Regression analysis was conducted to compare IMAs in different planes before and after the staged OLIF surgery. Significant three-dimensional correction was observed in 70 intervertebral segments following the first-stage OLIF. The wedge angles decreased from 5.2°± 4.2° to 2.7°± 2.4° (P < 0.001). The lordosis angles increased from 5.1°± 5.9° to 7.8°± 4.6° (P = 0.014), while the axial rotation angles decreased from 3.8°± 2.6° to 2.3°± 2.1° (P < 0.001). Linear regression analysis revealed a positive correlation between wedge angles and axial angles preoperatively (P < 0.001, r = 0.43), as well as between corrected wedge angles and corrected axial angles (P < 0.001, r = 0.42). This study demonstrated that intervertebral motions had a correlation between coronal and axial planes in lumbar degenerative scoliosis. First-stage OLIF was efficient at correcting segmental scoliosis by inserting cages while correcting rotation deformity simultaneously, as well as improving the sagittal spinopelvic parameters.

Idiopathic adolescent scoliosis and obesity: prevalence study.

Adolescent idiopathic scoliosis (AIS) is a three-dimensional spinal deformity that affects 5% of the population. This pathology has multiple known etiological factors such as family predisposition, female gender, low body mass index, decrease in lean and fat masses. However, recent studies suggest that ciliary dysfunction could be the origin of certain types of obesity and AIS. This study aims to verify the existence of a link between these two pathologies. A retrospective, cross-sectional, descriptive and monocentric study, based on a cohort of adolescents with obesity treated in a paediatric rehabilitation centre for specific care between 1 January 2010 and 1 January 2019. The prevalence of AIS was calculated by radiographic measurements. The diagnosis of AIS was established if the Cobb angle was ≥ 10°, associated with intervertebral rotation. 196 adolescents with obesity were included in the study (mean age 13.2years, mean BMI 36kg/cm2, gender ratio 2.1 of female to male.) The prevalence of AIS in adolescents with obesity was 12.2%, twice the prevalence of AIS in the general population. The characteristics of AIS in adolescents with obesity are predominantly female, 58.3% left thoracolumbar or lumbar principal curvatures, mean Cobb angle 26° and progressive in 29% of cases. Our study established a correlation between AIS and obesity with a higher prevalence than in the general population. The morphology of these adolescents makes screening for AIS more difficult.

Can semirigid fixation of the rostral instrumented segments prevent proximal junctional kyphosis in the case of long thoracolumbar fusions? A finite element study.

Proximal junctional kyphosis (PJK) is a relatively common complication following long instrumented posterior spinal fusion. Although several risk factors have been identified in the literature, previous biomechanical studies suggest that one of the leading causes is the sudden change in mobility between the instrumented and noninstrumented segments. The current study aims to assess the biomechanical effect of 1 rigid and 2 semirigid fixation techniques (SFTs) on developing PJK. Four T7-L5 finite element (FE) models were developed: 1) intact spine; 2) 5.5-mm titanium rod from T8 to L5 (titanium rod fixation [TRF]); 3) multiple rods from T8 to T9 connected with titanium rod from T9 to L5 (multiple-rod fixation [MRF]); and 4) polyetheretherketone rod from T8 to T9 connected with titanium rod from T9 to L5 (PEEK rod fixation [PRF]). A modified multidirectional hybrid test protocol was used. First, a pure bending moment of 5 Nm was applied to measure the intervertebral rotation angles. Second, the TRF technique's displacement from the first loading step was applied to the instrumented FE models to compare the pedicle screw stress values in the upper instrumented vertebra (UIV). In the load-controlled step, at the upper instrumented segment, the intervertebral rotation values relative to TRF increased by 46.8% and 99.2% for flexion, by 43.2% and 87.7% for extension, by 90.1% and 137% for lateral bending, and by 407.1% and 585.2% for axial rotation, in the case of MRF and PRF, respectively. In the displacement-controlled step, maximum pedicle screw stress values at the UIV level were highest in the case of TRF (37.26 MPa, 42.13 MPa, 44.4 MPa, and 44.59 MPa for flexion, extension, lateral bending, and axial rotation, respectively). Compared to TRF, in the case of MRF and PRF, the screw stress values were reduced by 17.3% and 27.7% for flexion, by 26.6% and 36.7% for extension, by 6.8% and 34.3% for lateral bending, and by 49.1% and 59.8% for axial rotation, respectively. FE analysis has shown that the SFTs increase the mobility at the upper instrumented segment and therefore provide a more gradual transition in motion between the instrumented and rostral noninstrumented segments of the spine. In addition, SFTs decrease the screw loads at the UIV level and hence could help reduce the risk for PJK. However, further investigations are recommended to evaluate the long-term clinical usefulness of these techniques.

Biomechanical Response of Four Roussouly's Sagittal Alignment Lumbar to Degeneration of Different Parts of Intervertebral Disc: Finite Element Model Analysis

BackgroundSpinal degeneration with age is commonly accompanied by excessive kyphosis and low-back pain, however, little is known about the connection between lumbar sagittal morphology and its degenerative biomechanics. This study investigates the biomechanical response of four Roussouly's sagittal alignment lumbar to degeneration of various parts of the intervertebral disc (IVD) based on threedimensional finite element (FE) models. MethodsUsing Roussouly's type parametric FE models, material properties of the degenerate nucleus populous (NP), annulus fibrosis matrix (AFM), and collagen fibers were assumed to be half of the intact IVD. A follower preload and vertical force were applied to simulate physical standing posture. Resultsthe reduced strength of the NP and AFM led to the increase of lumbar anteflexion, while the fiber mechanical properties have little effect on it. When facing IVD degeneration, Type 1 lumbar showed increased intradiscal pressures (IDPs) and fiber stress at the L1-2 and L4-S1 segments. Type 2 lumbar exhibited the highest lumbar anteflexion and pelvic rearward rotation, as well as increased IDPs among the models. Type 3 lumbar had the best biomechanical stability. Type 4 lumbar showed the higher AFM stress but the lower IDPs among the four types. ConclusionsIVD degeneration generated sagittal imbalance by increasing lumbar anteflexion movement (i.e., loss lordosis) and pelvic rearback rotation. The biomechanical response of the four Roussouly's lumbar types differed in intervertebral rotation and stress distribution.

Cervical Spine Finite Element Models for Healthy Subjects: Development and Validation

Abstract Finite element modeling is a popular method for predicting kinematics and kinetics in spine biomechanics. With the advancement of powerful computational equipment, more detailed finite element models have been developed for the various spine segments. In this study, five detailed finite element models of the cervical spine are developed and validated. The geometric boundaries of the vertebrae are determined from computed tomography (CT) scans of five female subjects. The models include the C2–C7 vertebrae, intervertebral discs, nuclei, endplates, and five major ligaments (anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), ligamentum flavum (LF), interspinous ligament (ISL), and capsular ligament (CL)). The ligaments follow nonlinear stress–strain curves whereas all other parts adopt linear material properties. All the material properties are taken from existing literature. The mesh convergence test is performed under flexion/extension. For flexion/extension motion, a pure moment is applied at the top surface of the odontoid process of the C2 vertebra while nodes at the bottom surface of the C7 vertebra are fixed in all directions. The models are extensively validated in flexion/extension, lateral bending, and axial rotation against experimental and finite element studies in the literature. Intervertebral rotation and range of motion are studied under different loading conditions found in the literature. This research also investigates intersubject variability for the cervical spine among five finite element models from five different subjects. Predicted angular displacements and ranges of motion of the current models are consistent with the literature. The validated models are expected to be applicable to simulate neck-related trauma like whiplash and high-g acceleration, among other scenarios.

P14. Analysis of physiological stress shielding within the lumbar musculoskeletal system as a consequence of mechanical adaptations associated with bilateral and unilateral low back pain: a finite element study

<h3>BACKGROUND CONTEXT</h3> Low back pain (LBP) is a public health crisis with nearly 85% of cases considered idiopathic. With the emergence of research analyzing the role of the thoracolumbar fascia (TLF) in spinal biomechanics, it is possible that the fascia may play a role in the progression of LBP. Previous studies have demonstrated changes to the TLF thickness and shear strain, as well as stiffness and morphological changes within lumbar spine-stabilizing muscles (eg, erector spinae [ES] and multifidus [MF]) in LBP patients. Such modifications to lumbar soft tissues suggest the plausibility of stress shielding, defining a load allocation bias, within the lumbar spine's soft tissues. <h3>PURPOSE</h3> The aim of this study is to develop and compare finite element models representing healthy, along with both bilateral and unilateral LBP-affected lumbar musculoskeletal systems to determine the potential for stress shielding within the lumbar spine from soft tissue property augmentation associated with LBP. <h3>METHODS</h3> Using a finite element platform, three models depicting the lumbar musculoskeletal system undergoing trunk flexion were created and compared. The first model represented the tissues of a healthy lumbar spine. The remaining models depicted lumbar soft tissues reflective of bilateral LBP (bLBP) and unilateral LBP (uLBP) patients. Each model was composed of vertebrae, intervertebral discs (IVDs) and soft tissues (including the MF, ES, TLF and tendons) from L1-S1. Material properties were selected from published literature. For the bLBP model, tissues on either side of the vertebral column were modified to reflect the changes in morphology and stiffness in the MF, and TLF as documented in literature involving bLBP patients. For the uLBP model, the MF and TLF located laterally to the right of the vertebral column ("symptomatic tissues") were augmented to reflect changes found within clinical studies involving uLBP patients. Remaining uLBP tissues were unchanged. Relevant model context of use validation preceded testing. <h3>RESULTS</h3> Validation was achieved as results demonstrated agreement in IVD pressure and intervertebral rotation with clinical data and in silico spine models. Compared to the healthy model, the cumulative average tension exhibited by soft tissues in the bLBP and uLBP model increased by 15.6 and 9.24%, respectively. The average tension exhibited by the bLBP model's MF, ES, and TLF changed by 13.0, -4.03, and 15.6%, while the uLBP model's symptomatic MF, ES, and TLF exhibited changes of 19.0%, -10.4%, and 16.1%, respectively. <h3>CONCLUSIONS</h3> The bLBP and uLBP models exhibited an increase in soft tissue tension by 18.4kPa and 10.9kPa relative to the healthy model soft tissues. In each LBP model, 99.8% of the overall stress increase, relative to the healthy model, was distributed towards the TLF. This demonstrates potential for the TLF in both the bLBP and uLBP scenarios to withstand the majority of increased tension, indicating a stress allocation bias within the lumbar soft tissues. This may initiate stress shielding whereby the TLF prevents adjacent spine-stabilizing soft tissues, such as the MF and ES, from receiving loading. Tissues may thus undergo atrophy and become less capable to withstand loading. To compensate, patients may depend on additional soft tissues, leading to irregular muscle activation and force balances, trapping the soft tissues in cyclical stress shielding. Ultimately, stress shielding within lumbar soft tissues may potentially lead to the progression of LBP. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

66. Can classification systems and baseline radiographic findings guide surgical technique selection for degenerative spondylolisthesis?

<h3>BACKGROUND CONTEXT</h3> The role of fusion in degenerative spondylolisthesis (DS) is controversial. The Clinical and Radiographic Degenerative Spondylolisthesis (CARDS) and Degenerative Spondylolisthesis Instability Classification (DSIC) systems were developed to assist surgeons in surgical technique selection based on individual patient characteristics. These systems have not been clinically validated. Additionally, it is unclear if baseline radiographic findings such as slip magnitude, angular and translational motion, and facet effusion are useful in guiding technique selection. <h3>PURPOSE</h3> The purpose of this study was to determine if outcomes vary with different surgical techniques across the CARDS and DSIC categories and with certain baseline radiographic findings. <h3>STUDY DESIGN/SETTING</h3> Prospective cohort study performed at one Swiss and one American spine center. <h3>PATIENT SAMPLE</h3> A total of 508 degenerative spondylolisthesis patients undergoing surgical treatment. <h3>OUTCOME MEASURES</h3> Core Outcomes Measure Index (COMI) at 3 months and 12 months postoperatively. <h3>METHODS</h3> DS patients undergoing surgery were enrolled at two institutions in Switzerland and the United States, and classified according to the CARDS and DSIC systems. MRIs were analyzed for Pfirrmann grade, disc height loss, presence of Schmorl's nodes, Modic changes, central and foraminal stenosis severity, magnitude of listhesis, magnitude of facet joint effusion, and facet joint angle. Dynamic radiographs were analyzed for magnitude of listhesis, disc height, bony apposition, kyphosis, translation, and intervertebral rotation. The Core Outcomes Measure Index (COMI) was completed at baseline, 3 months, and 12 months postoperatively. Due to small numbers in some subgroup analyses, patients treated with decompression alone or decompression with uninstrumented fusion were combined for analysis (uninstrumented group) as were patients treated with decompression and posterolateral instrumented fusion or decompression with posterolateral and interbody instrumented fusion (instrumented group). Unadjusted analyses and mixed effect models compared COMI scores between the two surgery technique groups (uninstrumented vs instrumented), stratified by CARDS and DSIC category and radiographic characteristics over time. Reoperation rates were also compared between the surgery technique groups stratified by CARDS and DSIC category. <h3>RESULTS</h3> A total of 508 patients were enrolled in the study, 460 had sufficient data to be classified according to CARDS, 459 could be classified according to DSIC, and 490 had radiographic images available for analysis. Seven percent were classified as CARDS A, 28% as CARDS B, 48% as CARDS C, and 17% as CARDS D (CARDS A most "stable", CARDS D least "stable"). 2% were classified as DSIC 1, 80% as DSIC 2, and 17% as DSIC 3 (DSIC 1 most "stable, DSIC 3 least "stable"). One hundred thrity-three patients (26%) underwent decompression alone, 30 (6%) underwent decompression and uninstrumented fusion, 42 (8%) underwent decompression and posterolateral instrumented fusion, and 303 (60%) underwent decompression with posterolateral and interbody instrumented fusion. Patients in the least "stable" categories tended to be less likely to be treated with an uninstrumented technique (CARDS D 19% and DSIC 3 21% vs 32% for the other categories, p=0.10 for CARDS, p=0.02 for DSIC). There were no significant differences in 3- or 12-month COMI scores between surgical technique groups stratified by CARDS or DSIC category in the unadjusted or adjusted analyses. In the unadjusted analyses, there was a trend toward less improvement in 12-month COMI change score in the CARDS D patients in the uninstrumented group compared to the instrumented group (-3.01 vs -3.88, p=0.10). Reoperation rates were not significantly different between the surgical technique groups stratified by CARDS and DSIC category. There were no significant differences between the surgical technique groups across the different radiographic characteristics. There was a nonsignificant trend toward more improvement in the instrumented group in patients with severe foraminal stenosis and larger facet joint effusions. <h3>CONCLUSIONS</h3> In general, outcomes for uninstrumented and instrumented surgical techniques were similar across the DSIC and CARDS categories. There was a trend toward less improvement in the CARDS D patients treated with uninstrumented techniques, suggesting that in patients with kyphosis (the defining feature of the CARDS D category) better outcomes may be associated with instrumentation. Baseline radiographic findings were generally not associated with different outcomes across the surgical technique groups. The major limitation of this study was the low numbers in the CARDS D (n=15) and DSIC 3 (n=17) uninstrumented groups, likely due to surgeons choosing to avoid uninstrumented techniques in these patients. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Influence of Sagittal Lumbopelvic Morphotypes on the Range of Motion of Human Lumbar Spine: An In Vitro Cadaveric Study.

Background: Although spinopelvic radiographs analysis is the standard for a pathological diagnosis, it cannot explain the activities of the spine in daily life. This study investigates the correlation between sagittal parameters and spinal range of motion (ROM) to find morphological parameters with kinetic implications. Methods: Six L1–S1 human lumbar specimens were tested with a robotic testing device. Eight sagittal parameters were measured in the three-dimensional model. Pure moments were applied to simulate the physiological activities in daily life. Results: The correlation between sagittal parameters and the ROM was moderate in flexion and extension, but weak in lateral bending and rotation. In flexion–extension, the ROM was moderately correlated with SS and LL. SS was the only parameter correlated with the ROM under all loading conditions. The intervertebral rotation distribution showed that the maximal ROM frequently occurred at the L5–S1 segment. The minimal ROM often appeared near the apex point of the lumbar. Conclusion: Sagittal alignment mainly affected the ROM of the lumbar in flexion and extension. SS and apex may have had kinetic significance. Our findings suggest that the effect of sagittal parameters on lumbar ROM is important information for assessing spinal activity.

Relationship between facet joint opening on CT and facet joint effusion on MRI in patients with lumbar spinal stenosis: analysis of a less invasive decompression procedure.

Both facet joint opening (FJO) on CT and facet joint effusion (FJE) on MRI are reportedly indicators of segmental instability in the lumbar facet joints of patients with lumbar spinal stenosis (LSS). However, no study has investigated both parameters simultaneously. Therefore, the association between these findings and which parameter is better for predicting clinical outcomes after surgical treatment remains unclear. The purpose of this study was to investigate the relationship between FJO and FJE in patients who underwent less invasive decompression procedures for LSS and to investigate the impact of these findings on clinical outcomes. This study included 1465 lumbar levels (L1-2 to L5-S1) in 293 patients who underwent less invasive surgery for LSS and had ≥ 5 years of follow-up. FJO was defined as joint space widening ≥ 2 mm on preoperative axial CT images. FJE was defined as fluid effusion in the facet joint on preoperative axial T2-weighted MR images. The characteristics and distributions of FJO and FJE were investigated with other preoperative radiological findings. The association between need for further surgery and FJO/FJE was analyzed according to intervertebral level. FJO was observed at 402 levels (27%), and FJE was found at 306 levels (21%). The correspondence rate between FJO and FJE was 70% (kappa 0.195, p < 0.01). One hundred thirty-seven levels (9%) had both FJO and FJE. Levels with both FJO and FJE more commonly had lateral olisthesis, lateral wedging, and axial intervertebral rotation than other levels (p < 0.001). Levels with both FJO and FJE were more likely than other levels to need further surgery (OR 2.42, p = 0.027). The correspondence rate between FJO and FJE was not high. However, multivariate analysis showed that levels with both FJO and FJE had a higher risk of requiring further surgery than those with other radiological findings, such as lateral olisthesis, lateral wedging, and axial intervertebral rotation. Patients with levels with both FJO and FJE need careful long-term follow-up after undergoing a less invasive decompression procedure.

P48. The use of motion metrics parameters to predict postoperative patient reported outcomes in patients with lumbar stenosis and spondylolisthesis

<h3>BACKGROUND CONTEXT</h3> Lumbar stenosis is a common spinal pathology and studies have shown that surgical treatment is often more effective than nonoperative management. Surgical options for the treatment of lumbar stenosis include decompression alone or decompression with fusion. Patients are often chosen for decompression with fusion when there is perceived instability; however, it is often unclear which radiographic parameters indicate instability requiring fusion. <h3>PURPOSE</h3> To evaluate the potential of motion metrics in predicting postop Patient Reported Outcomes (PROs) in patients with lumbar stenosis undergoing decompression with fusion or decompression alone. We hypothesize that patients with abnormal preoperative motion parameters will achieve better outcomes with decompression with fusion, and that patients with normal preop motion metrics will achieve better outcomes with decompression alone. <h3>STUDY DESIGN/SETTING</h3> Retrospective single center cohort study. <h3>PATIENT SAMPLE</h3> Patients treated for single level lumbar stenosis with spondylolisthesis by either decompression only or decompression plus fusion. <h3>OUTCOME MEASURES</h3> PROs (ODI, VAS and NRS), Angular Motion, Intervertebral Translation, Sagittal Plane Shear Index (SPSI), Spondylolisthesis Index, Anterior and Posterior Disc Integrity Index, Global ROM. <h3>METHODS</h3> This preliminary analysis includes 16/40 patients. Preop and 1-year postop flexion/extension X-ray images were analyzed with previously validated motion analysis software. Since the mechanical integrity of soft-tissues cannot be assessed unless the soft-tissues are sufficiently stressed, patients with <3 deg of preop intervertebral rotation between flexion and extension were excluded. Demographic data were obtained from medical records, including age, gender, length of stay, comorbidities and PROs. <h3>RESULTS</h3> Of the 16 patients, 12 (75%) were female and 4 (25%) were male. Ages ranged from 33 to 77 years old with an average of 64 at the time of surgery. Two patients had surgery at L3-L4 (12%) and 14 had surgery at L4-L5 (88%). All 16 patients received decompression with fusion. The 95% confidence interval of a dataset that includes 384 radiographically normal asymptomatic volunteers was used to define normal limits of motion. SPSI > 2 indicates that the translation per degree of rotation was beyond the upper limit of normal. Preop SPSI was measured at 16 treatment levels and 50 non-treatment levels. Preop SPSI at the treatment level was 1.4±2.5 [-4.1 to 6.4] with 7 patients having SPSI>2 and 9 subjects having SPSI<=2. Preop SPSI at non-treatment levels was 0.6±1.9 [-2.5 to 9.9] and the postop SPSI at non-treatment levels was 0.4±1.5 [-2 to 4.8]. <h3>CONCLUSIONS</h3> SPSI is an objective measure of sagittal plane instability that may inform physicians of the need for fusion. In this preliminary analysis, the mean preop SPSI at the treatment level approached the upper limit of normal, while the mean at non-treatment levels was near the center of normal. There were 43.8% of patients who had abnormal preop SPSI values at the treatment level. Upon review of the PROs we will determine if preop SPSI is predictive of clinical outcome success, and if other novel metrics can be used along with SPSI to inform the optimal treatment pathway. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Influence of structural and material property uncertainties on biomechanics of intervertebral discs - Implications for disc tissue engineering

This study investigated how variations of structural and material properties of human intervertebral discs (IVDs) affect the biomechanical responses of the IVDs under simulated physiological loading conditions using a stochastic finite element (SFE) model. An SFE method, which combined an anatomic FE model of human lumbar L3-4 segment and probabilistic analysis of its structural and material properties, was used to generate a dataset of 500 random disc samples with varying structural and material properties. The sensitivity of the biomechanical responses, including intervertebral displacements/rotations, intradiscal pressures (IDP), fiber stresses and matrix strains of annulus fibrosus (AF), were systematically quantified under various physiological loading conditions, including a 500N compression and 7.5Nm moments in the 3 primary rotations. Significant variations of the IDPs, IVD displacements/rotations, and stress/strain distributions were found using the dataset of 500 ramdom disc samples. Under all the loading conditions, the IDPs were positively correlated with the Poisson's ratio of the NP (r=0.46 to 0.75, p=0.004-0.001) and negatively with the Young's modulus of the annulus matrix (r=-0.48 to -0.65, p=0.003-0.001). The primary intervertebral rotations were significantly affected by the Young's modulus of the annulus matrix (r=-0.44 to -0.71, p=0.001-0.032) and the orientations of the annular fibers (r=-0.45 to -0.69, p=0.001-0.029). The heterogeneity of structures and material properties of the IVD had distinct effects on the biomechanical performances of the IVD. These data could help improve our understanding of the intrinsic biomechanics of the IVD and provide references for optimal design of tissue engineered discs by controlling structural and material properties of the disc components.

Analysis of translation and angular motion in loaded and unloaded positions in the lumbar spine

Background ContextAbnormalities in intervertebral rotation and translation are important to diagnosis and treatment planning for common spinal disorders. Tests that do not sufficiently load the spine can result in mis-diagnosed motion abnormalities. Upright flexion and extension x-rays are commonly used despite known limitations. Additional evidence is needed in support of preliminary studies suggesting that the change from standing to supine may sufficiently stress the spine to diagnose motion abnormalities. PurposeCompare intervertebral translation between flexion and extension to translation between upright and supine positions in a representative clinical population. Study Design/SettingProspective analysis of images retrospectively collected from routine clinical practices. MethodsAfter obtaining IRB approval for analysis of previously obtained images, patients were identified via chart reviews where a neutral-lateral x-ray and an MRI or CT exam were obtained for diagnosis of a spinal disorder and where flexion-extension x-rays had been obtained to help diagnose abnormal intervertebral motion. The mid-sagittal slice from the MRI or CT exam was paired with the neutral-lateral radiograph. Intervertebral translation at the L4-L5 and L5-S1 levels between supine and standing and between flexion and extension were measured from the images using previously validated methods. The translations were classified as normal or abnormal with reference to a previously obtained database of intervertebral motion in radiographically normal and asymptomatic volunteers. ResultsAt the L5-S1 level in particular, there tended to be greater translation between the supine and standing than between upright flexion and extension. On average, translations were below that found in asymptomatic volunteers. No abnormal translations were detected from flexion-extension radiographs whereas approximately 7% of levels had abnormal translations between supine and upright positions. ConclusionsIntervertebral translations between supine and standing, measured using the mid-sagittal slice from a MRI or CT exam and a lateral x-ray with the patient standing can help to identify abnormal motion. This would be particularly valuable for patients with limited flexion and extension. This study thereby adds to the evidence in support of measuring intervertebral motion between the supine and upright positions to detect abnormal intervertebral motion.

Efficacy of Integrating Cervical Posture Correction With Lumbar Stabilization Exercises for Mechanical Low Back Pain: A Randomized Blinded Clinical Trial.

Although current lumbar stabilization exercises are beneficial for chronic mechanical low back pain, further research is recommended focusing on global spinal alignment normalization. This randomized, controlled, blinded trial was conducted to determine the effects of adding cervical posture correction to lumber stabilization on chronic mechanical low back pain. Fifty adult patients (24 males) with chronic mechanical low back pain and forward head posture received 12 weeks treatment of either both programs (group A) or lumbar stabilization (group B). The primary outcome was back pain. The secondary outcomes included the craniovertebral angle, Oswestry Disability Index, C7-S1 sagittal vertical axis, and sagittal intervertebral movements. The multivariate analysis of variance indicated a significant group-by-time interaction (P = .001, partial η2 = .609). Pain, disability, C7-S1 sagittal vertical axis, and l2-l3 intervertebral rotation were reduced in group A more than B (P = .008, .001, .025, and .001). Craniovertebral angle was increased in A when compared to B (P = .001). However, there were no significant group-by-time interactions for other intervertebral movements. Within-group comparisons were significant for all outcomes except for craniovertebral angle within patients in the control group. Adding cervical posture correction with lumber stabilization for management of chronic low back pain seemed to have better effects than the application of a stabilization program only.

Combined Effects of Graded Foraminotomy and Annular Defect on Biomechanics after Percutaneous Endoscopic Lumbar Decompression: A Finite Element Study.

Percutaneous endoscopic technology has been widely used in the treatment of lumbar disc stenosis and herniation. However, the quantitative influence of percutaneous endoscopic lumbar decompression on spinal biomechanics of the L5–S1 lumbosacral segment remains poorly understood. Hence, the objective of this study is to investigate the combined effects on the biomechanics of different grades of foraminotomy and annular defect for the L5–S1 segment. A 3D, nonlinear, detailed finite element model of L4–S1 was established and validated. Changes in biomechanical responses upon stimulation to the intact spine during different degrees of resection were analyzed. Measurements included intervertebral rotation, intradiscal pressure, and the strain of disc structure under flexion, extension, left/right lateral bending, and left/right axial rotation under pure bending moments and physiological loads. Compared with the intact model, under prefollower load, annular defect slightly decreased intervertebral rotation by −5.0% in extension and 2.2% in right axial rotation and significantly increased the mean strain of the exposed disc by 237.7% in all loading cases. For right axial rotation, unilateral total foraminotomy with an annular detect increased intervertebral rotation by 29.5% and intradiscal pressure by 57.6% under pure bending moment while the maximum corresponding values were 9.8% and 6.6% when the degree of foraminotomy was below 75%, respectively. These results indicate that percutaneous endoscopic lumbar foraminotomy highly maintains spinal stability, even if the effect of annular detect is taken into account, when the unilateral facet is not totally removed. Patients should avoid excessive extension and axial rotation after surgery on L5–S1. The postoperative open annular defect may substantially increase the risk of recurrent disc herniation.

Accuracy on the preoperative assessment of patients with adolescent idiopathic scoliosis using biplanar low-dose stereoradiography: a comparison with computed tomography

BackgroundAlthough computed tomography (CT) is commonly used to diagnose the scoliotic spine in patients with adolescent idiopathic scoliosis (AIS) preoperatively, it is limited by the high radiation and prone scanning position. Recently, a new biplanar stereoradiography (EOS) was used to image the scoliotic spine in an upright posture with significantly less radiation in non-severe AIS subjects. However, its reliability to assess preoperative AIS patients remains unreported. Hence, the purpose of this study is to compare the scoliotic curvature between prone (CT) and upright positions (EOS) in preoperative AIS patients.MethodsThirty-three pre-operative AIS patients (mean age:18.4 ± 4.2) were recruited. EOS was used to scan the whole thoracic spine at upright position. Whereas on the same day, a conventional CT scan was used to evaluate the spine in prone position. The three-dimensional reconstruction of EOS and CT of the spine were then generated. Using previous validated techniques, multiple scoliotic parameters in both modalities were determined. The agreement between the two modalities was compared using the Bland-Altman test, whereas the correlation was assessed by the intraclass correlation coefficient (ICC).ResultsThe mean ICC (prone and upright) of intra-rater/inter-rater reliabilities for the measured parameters were 0.985,0.961/0.969,0.903, respectively. Thoracic Cobb angles, intervertebral wedging and lumbar lordosis correlated significantly between upright EOS imaging radiographs (62.9 ± 9.3°,6.4 ± 2.9° and 48.8 ± 12.4°) and prone CT (47.3 ± 10.0°,5.8 ± 2.7° and 27.9 ± 11.4°; P < 0.001). The apical vertebral wedging and apical intervertebral disc wedging showed a good correlation among the two modalities (upright, 6.5 ± 3.5° and 6.4 ± 2.9°; prone, 6.5 ± 3.6° and 5.8 ± 2.7°; R2 ≥ 0.94; P < 0.01). Similarly, there was significant correlation in apical intervertebral rotation (R2 = 0.834; P < 0.01) between the prone CT (3.4 ± 3.0°) and upright EOS (3.8 ± 3.2°). In addition, the Cobb angle was significantly larger in upright EOS (62.9 ± 9.3°) than in prone CT (47.3 ± 10.0°, P < 0.01) position. There was significant underestimation on scoliotic severity in the prone position when compared with upright position.ConclusionsImportantly, the image acquisition and reconstruction from EOS can better provide accurate three-dimensional spinal representations of the scoliotic curvature in preoperative AIS patients. Moreover, our findings suggested that scoliotic curvatures in preoperative AIS patients can be largely represented by both imaging modalities despite the difference in body positioning.

Alterations in the Geometry, Fiber Orientation, and Mechanical Behavior of the Lumbar Intervertebral Disc by Nucleus Swelling.

Soft tissues observed in clinical medical images are often prestrained in tension by internal pressure or tissue hydration. For a native disc, nucleus swelling occurs in equilibrium with osmotic pressure induced by the high concentration of proteoglycan in the nucleus. The objective of this computational study was to investigate the effects of nucleus swelling on disc geometry, fiber orientation, and mechanical behavior by comparing those of prestrained and zero-pressure (unswelled) discs. Thermoelastic analysis techniques were repurposed in order to determine the zero-pressure disc geometry which, when pressurized, matches the prestrained disc geometry observed in clinical images. The zero-pressure geometry was then used in simulations to approximately represent a degenerated disc, which loses the ability of nucleus swelling but has not undergone distinct soft tissue remodeling/disruption. Our simulation results demonstrated that the loss of nucleus swelling caused a slight change in the disc geometry and fiber orientation, but a distinct deterioration in the resistance to intervertebral rotations including sagittal bending, lateral bending, and axial torsion. Different from rotational loading, in compression (with a displacement of 0.45 mm applied), a much larger stiffness (3.02 KN/mm) and a greater intradiscal pressure (IDP) (0.61 MPa) were measured in the zero-pressure disc, compared to the prestrained disc (1.41 KN/mm and 0.52 MPa). This computational study could be useful to understand mechanisms of disc degeneration, and guide the future design of disc tissue engineering material and biomimic disc implants.

Axial plane characteristics of thoracic scoliosis and their usefulness for determining the fusion levels and the correction technique.

There is insufficient information regarding axial plane characteristics of scoliosis despite its 3D nature. The posterior-anterior vertebral vector (VV) has been proposed to characterize the axial plane appearances of the thoracic scoliosis. This study aimed to highlight the importance of knowledge of axial plane features when determining fusion levels and correction techniques of thoracic curves. Altogether, 233 thoracic curves were analyzed using the VV after proving its usability instead of 3D angles to determine axial plane parameters such as apical vertebral (APV) axial rotations, APV lateral displacement, and intervertebral rotations (IVR). K-means clustering and regression analysis were used to identify axial plane curve patterns and determine the relationship between the coronal angles and axial plane characteristics, respectively. A close correlation was found between 3D angles and VV projected angles. Eight axial plane clusters were distinct, exhibiting different lateral APV displacement toward the interacetabular axis with relatively small axial rotations and a simultaneous decrease in sagittal curves. The regression analysis showed that the correlation of coronal curve magnitude was significantly stronger (r = 0.78) with APV lateral translation than with APV axial rotation (r = 0.65). Based on these findings, the primary goal of scoliosis correction should focus on minimizing lateral translation rather than eliminating axial rotation. Knowing the IVR in the axial plane helps accurately determine the limits of the structural curves. VV-based axial views can facilitate the accurate determination of the end vertebrae and selection of the appropriate correction technique of the curve. These slides can be retrieved under Electronic Supplementary Material.