The lumbar supraspinous ligament demonstrates increased material stiffness and strength on its ventral aspect

The Posterior Ligamentous Complex: Anatomic and Biomechanical Considerations in Injury Classification and Management

The posterior ligamentous complex (PLC) provides critical structural support in the thoracolumbar spine. Its role in resisting progressive flexion is particularly important at the thoracolumbar junction due to the transition from the rigid thoracic spine to the more mobile lumbar region. Each component of the PLC contains anatomic features that contribute to both the structure and function of the PLC as a whole. Understanding the nuances of each structure is important in determining injury severity and may serve as a foundation for future directions of research. Violation of the PLC results in an unstable spine, thus requiring surgical management. It is associated with greater injury severity and neurologic deficit in patients who sustain thoracolumbar fractures, which adds complexity to the postoperative course and patient outcomes. Although plain radiographs and CT scans provide reliable indirect measures of PLC disruption, these modalities may be subject to diminished sensitivity based on patient positioning and do not directly measure soft-tissue injury. Modern classification systems include the integrity of the PLC in surgical decision making, and care must be taken to scrutinize the possibility of ligamentous disruption before proceeding with nonsurgical management to avoid adverse patient outcomes.

A new classification of lumbar Basstrup's disease based on radiographic and clinical symptoms

OBJECTIVE

To propose a new classification method for lumbar Basstrup's disease based on radiographic and clinical symptoms, and to test its credibility and reproducibility.

METHODS

A retrospective analysis of 116 patients with complete data of lumbar Basstrup's disease in our hospital from January 2019 to January 2022, radiological imaging including X-ray, CT and MRI, were divided into two main types according to the number of segments: type I (single segment) and type II (multiple segments), each type was divided into a total of eight subtypes according to the degree of degeneration: Ia, Ib, Ic, Id, IIa, IIb, IIc, IId; it was further divided into 16 subtypes according to the presence or absence of clinical symptoms (i.e. low back pain or/and lower limb neurological symptoms: no 0, yes 1): Ia0, Ia1, Ib0, Ib1, Ic0, Ic1, Id0, Id1; IIa0, IIa1, IIb0, IIb1, IIc0, IIc1, IId0, IId1.The 116 patients with Basstrup's disease were successively typed twice (1 month interval) by five physicians according to the new classification method, and the reliability and reproducibility of the new classification were assessed using the Kappa consistency test.

RESULTS

Among 116 patients with lumbar Basstrup's disease: there were 60 cases of type I (single segment), accounting for 51.72%, including Ia 19 cases, Ib 16 cases, Ic 10 cases, and Id 15 cases; there were 56 cases of type II (multiple segments), accounting for 48.28%, including IIa 10 cases, IIb 20 cases, IIc 14 cases, and IId 12 cases. Of the 116 patients, 47 cases had no clinical symptoms (Ia0 16 cases, Ib0 3 cases, Ic0 6 cases, Id0 1 case, IIa0 8 cases, IIb0 2 cases, IIc0 10 cases, IId0 1 case), accounting for 40.52%; 69 cases were accompanied by low back pain or/and lower extremity nerve symptoms (Ia1 3 cases, Ib1 13 cases, Ic1 4 cases, Id1 14 cases, IIa1 2 cases, IIb1 18 cases, IIc1 4 cases, IId1 11 cases), accounting for 59.48%.Five physicians completed two rounds of a total of 1160 typings, with inter-assessor typing agreement of 82.47% (80.17-85.34%) and a mean Kappa value of 0.723 (0.771-0.831); intra-assessor typing agreement of 82.76% (77.59-86.21%) and a mean Kappa value of 0.801 (0.742-0.841).

CONCLUSION

The new classification method for lumbar Basstrup's disease based on radiographic and clinical symptoms is simple, practical, with good credibility and reproducibility, and provides some guidance for clinical treatment.

Assessment of a fully-parametric thoraco-lumbar spine model generator with articulated ribcage

The present paper describes a novel user-friendly fully-parametric thoraco-lumbar spine CAD model generator including the ribcage, based on 22 independent parameters (1 posterior vertebral body height per vertebra + 4 sagittal alignment parameters, namely pelvic incidence, sacral slope, L1-L5 lumbar lordosis, and T1-T12 thoracic kyphosis). Reliable third-order polynomial regression equations were implemented in Solidworks to analytically calculate 56 morphological dependent parameters and to automatically generate the spine CAD model based on primitive geometrical features. A standard spine CAD model, representing the case-study of an average healthy adult, was then created and positively assessed in terms of spinal anatomy, ribcage morphology, and sagittal profile. The immediate translation from CAD to FEM for relevant biomechanical analyses was successfully demonstrated, first, importing the CAD model into Abaqus, and then, iteratively calibrating the constitutive parameters of one lumbar and three thoracic FSUs, with particular interest on the hyperelastic material properties of the IVD, and the spinal and costo-vertebral ligaments. The credibility of the resulting lumbo-sacral and thoracic spine FEM with/without ribcage were assessed and validated throughout comparison with extensive in vitro and in vivo data both in terms of kinematics (range of motion) and dynamics (intradiscal pressure) either collected under pure bending moments and complex loading conditions (bending moments + axial compressive force).

Intervertebral disc degeneration relates to biomechanical changes of spinal ligaments

BACKGROUND CONTEXT

The ligamentum flavum (LF), the inter- and supraspinous ligament (ISL&SSL) and the intertransverse ligament (ITL) are relevant spinal structures for segmental stability. The biomechanical effect of degeneration and aging on their biomechanical properties remains largely unknown.

PURPOSE

The aim of this study was to assess the material properties of the ITL, ISL&SSL and LF and to correlate parameters of biomechanical function with LF-thickness, intervertebral disc (IVD) degeneration and age.

STUDY DESIGN

Biomechanical cadaveric study.

METHODS

MRI- and CT-scans of 50 human lumbar segments (Th12-L5) were used to assess the ISL (acc. to Keorochana), the grade of IVD degeneration (acc. to Pfirrmann) and to quantify LF-thickness. The ITL, ISL&SSL and LF were resected in the neutral position of the spinal segment with a specifically developed method to conserve initial strain. Ramp to failure testing was performed (0.5 mm/s) to record initial tension, slack length, stiffness and ultimate strength. The relationship between the biomechanical characteristics and age and radiological parameters were analyzed. There are no study-specific conflicts of interest and no external funding was received for this study.

RESULTS

With aging, a significant reduction in initial tension (r=-0.5, p<.01) and ultimate strength (r=-0.41, p<.01) of the LF was observed, while the effect on LF-stiffness and the characteristics of the other ligaments was non-significant. IVD-degeneration was correlated with a significant reduction in stiffness (r=-0.47, p=.001; r=-0.36, p=.01) and ultimate strength (r=-0.3, p=.04; r=-0.36, p=.01) of the LF and ISL&SSL respectively and a significant reduction in initial tension (r=-0.4, p<.01) of the LF. For the ITL, no significant correlation was observed. Comparing Pfirrman 2 to 5, this reduction was 40% to 80% for stiffness 60% to 70% for ultimate strength and 88% for initial tension of the LF. ISL&SSL-stiffness between Kerorochana grade A and D differed significantly (p=.03), while all other comparisons were non-significant (p>.05). LF-thickness did not correlate with the biomechanical properties of the LF (p>.05).

CONCLUSIONS

Aging is primarily related to biomechanical changes to the LF. IVD-degeneration is related to a relevant reduction in stiffness and ultimate strength of the LF and ISL&SSL, with a similar trend for the ITL. The ISL-specific Keorochana grading system provides only minimal biomechanical information and LF-thickness does not provide biomechanical information.

CLINICAL SIGNIFICANCE

Patient age and the degenerative state of the IVD can be used to evaluate the biomechanical characteristics of the dorsal spinal ligaments, which can be helpful in selecting the optimal surgical procedure (e.g. in decompression surgery) for a specific situation.

A Comparison of Clinical Spinal Mobility Measures to Experimentally Derived Lumbar Spine Passive Stiffness

Spinal stiffness and mobility assessments vary between clinical and research settings, potentially hindering the understanding and treatment of low back pain. A total of 71 healthy participants were evaluated using 2 clinical assessments (posteroanterior spring and passive intervertebral motion) and 2 quantitative measures: lumped mechanical stiffness of the lumbar spine and local tissue stiffness (lumbar erector spinae and supraspinous ligament) measured via myotonometry. The authors hypothesized that clinical, mechanical, and local tissue measures would be correlated, that clinical tests would not alter mechanical stiffness, and that males would demonstrate greater lumbar stiffness than females. Clinical, lumped mechanical, and tissue stiffness were not correlated; however, gradings from the posteroanterior spring and passive intervertebral motion tests were positively correlated with each other. Clinical assessments had no effect on lumped mechanical stiffness. The males had greater lumped mechanical and lumbar erector spinae stiffness compared with the females. The lack of correlation between clinical, tissue, and lumped mechanical measures of spinal stiffness indicates that the use of the term "stiffness" by clinicians may require reevaluation; clinicians should be confident that they are not altering mechanical stiffness of the spine through segmental mobility assessments; and greater resting lumbar erector stiffness in males suggests that sex should be considered in the assessment and treatment of the low back.

Lumbar interspinous pressure pain threshold values for healthy young men and women and the effect of prolonged fully flexed lumbar sitting posture: An observational study

BACKGROUND

Low back pain (LBP) is a common condition with large burden worldwide. Exposure to prolonged sitting with a flexed lumbar posture has been suggested in the literature to be a potential risk factor for self-reported LBP. No study has previously investigated whether exposure to prolonged flexed sitting posture provokes discomfort/pain and decreased interspinous pressure pain thresholds for healthy young men and women without back pain, despite this being a suggested risk factor for LBP.

AIM

To investigate whether sitting in a prolonged flexed lumbar posture provokes discomfort and lowers interspinous pressure pain thresholds in the lumbar spine for healthy young men and women without previous LBP.

METHODS

This is a an observational before and after study of 26 participants (13 men, 13 women) between 20-35 years old. Algometry was used to examine the pain threshold for pressure applied between spinous processes of the lumbar spine L1-L5. Pressure algometer measures were performed in prone before and after participants were instructed to sit in a fully flexed posture for a maximum of 15 min or until discomfort was experienced in the low back (Borg CR10 = 7/10). Wilcoxon signed-rank test was used for analyze values from the before and after test conditions. Mann-Whitney U test was used to investigate potential gender difference.

RESULTS

Fully flexed lumbar spine sitting posture up to 15 min provoked temporary discomfort but the proportion of participants experiencing discomfort 7/10 in the low back was 62%. For all pain pressure threshold locations tested, there was a significant difference for the study population with moderate-large decreased (r = -0.56) pressure pain threshold after exposure to prolonged flexed sitting posture (P < 0.01). Comparisons between gender did not show any significant difference.

CONCLUSION

The result showed that exposure to fully flexed lumbar sitting posture for up to 15 min produced temporary discomfort in the low back in young healthy adults with no previous history of LBP and significantly reduced lumbar interspinous pressure pain thresholds. No gender-based differences were observed.

Finite element analysis of the influence of three-joint spinal complex on the change of the intervertebral disc bulge and height

This study evaluated the changes of height and bulging occurring in individual layers of the annulus fibrosus of the intervertebral disc for 3 load scenarios (axial compression, flexion, and extension). The numerical model of a single motion segment of the thoracic spine was analysed for 2 different configurations, ie, for the model of a physiological segment and a segment with the posterior column removed. In the physiological segment, all annulus fibrosus layers decrease in height regardless of the applied load, bulging outside the intervertebral disc. Removal of the posterior column increases mobility and disrupts the load transfer system, with the lamellae bulging into the intervertebral disc.

Adjacent Disc Stress Following Floating Lumbar Spine Fusion: A Finite Element Study

STUDY DESIGN

Experimental study.

PURPOSE

The study aimed to develop a finite element (FE) model to determine the stress on the discs adjacent to the fused segment following different types of floating lumbar spinal fusions.

OVERVIEW OF LITERATURE

The quantification of the adjacent disc stress following different types of floating lumbar fusions has not been reported. The magnitude of the stress on the discs above and below the floating fusion remains unknown.

METHODS

A computer-aided engineering-based approach using implicit FE analysis was employed to assess the stress on the lumbar discs above and below the floating fusion segment (L4-L5) following anterior and posterior lumbar spine fusions at one, two, and three levels (with and without instrumentation).

RESULTS

Both discs suprajacent and infrajacent to the floating fusion experienced increased stress, but the suprajacent disc experienced relatively high stress level. Instrumentation increased the stress on the discs suprajacent and infrajacent to the floating fusion, but the magnitude of stress on the suprajacent disc remained relatively high.

CONCLUSIONS

The FE model was employed under similar loading and boundary conditions to provide quantitative data, which will be useful for clinicians to understand the probable long-term effects of floating fusions.

Baastrup's Disease, Interspinal Bursitis, and Dorsal Epidural Cysts: Radiologic Evaluation and Impact on Treatment Options

Baastrup’s disease or "kissing spines syndrome" was first described as a cause of lumbar pain before computerized tomography (CT) and magnetic resonance imaging (MRI) scanning existed. The diagnosis was based on x-ray studies, which showed that the spinous processes, especially in the lower lumbar spine, became approximated to each other and this was a generator of positional back pain. Biomechanically, the interspinous and supraspinous ligaments that are degenerated in Baastrup's disease normally contribute significantly to sagittal alignment. Ligamentous stenosis and anterolisthesis would be the expected pathology with deterioration of these ligaments and were initially described on CT and MRI in patients with symptoms similar to Baastrup's disease as isolated individual case reports. This review will highlight the relationship between the various clinical presentations, biomechanics, and overlap of Baastrup's disease with interspinous bursitis, segmental stenosis, and instability, presenting them as a disease continuum rather than as separate disease processes.

Characterizing white matter tissue in large strain via asymmetric indentation and inverse finite element modeling

Characterizing the mechanical properties of white matter is important to understand and model brain development and injury. With embedded aligned axonal fibers, white matter is typically modeled as a transversely isotropic material. However, most studies characterize the white matter tissue using models with a single anisotropic invariant or in a small-strain regime. In this study, we combined a single experimental procedure - asymmetric indentation - with inverse finite element (FE) modeling to estimate the nearly incompressible transversely isotropic material parameters of white matter. A minimal form comprising three parameters was employed to simulate indentation responses in the large-strain regime. The parameters were estimated using a global optimization procedure based on a genetic algorithm (GA). Experimental data from two indentation configurations of porcine white matter, parallel and perpendicular to the axonal fiber direction, were utilized to estimate model parameters. Results in this study confirmed a strong mechanical anisotropy of white matter in large strain. Further, our results suggested that both indentation configurations are needed to estimate the parameters with sufficient accuracy, and that the indenter-sample friction is important. Finally, we also showed that the estimated parameters were consistent with those previously obtained via a trial-and-error forward FE method in the small-strain regime. These findings are useful in modeling and parameterization of white matter, especially under large deformation, and demonstrate the potential of the proposed asymmetric indentation technique to characterize other soft biological tissues with transversely isotropic properties.

Long-Term Effects of Segmental Lumbar Spinal Fusion on Adjacent Healthy Discs: A Finite Element Study

Study Design

Experimental study.

Purpose

The aim of the study was to develop a finite element (FE) model to study the long-term effects of various types of lumbar spinal interventions on the discs adjacent to the fused segment.

Overview of Literature

Earlier FE studies have been limited to one particular type of fusion and comparative quantification of the adjacent disc stresses for different types of surgical interventions has not been reported.

Methods

A computer aided engineering (CAE) based approach using implicit FE analysis assessed the stresses in the lumbar discs adjacent to the fused segment following anterior and posterior lumbar spine fusions at one, two and three levels (with and without instrumentation).

Results

It was found that instrumentation and length of fusion were the most significant factors in increasing adjacent level stresses in the lumbar discs.

Conclusions

In the present study, a calibrated FE model that examined spinal interventions under similar loading and boundary conditions was used to provide quantitative data which would be useful for clinicians to understand the probable long-term effect of their choice of surgical intervention.

Quantitative comparison of ligament formulation and pre-strain in finite element analysis of the human lumbar spine

Data has been published that quantifies the nonlinear, anisotropic material behaviour and pre-strain behaviour of the anterior longitudinal, supraspinous (SSL), and interspinous ligaments of the human lumbar spine. Additionally, data has been published on localized material properties of the SSL. These results have been incrementally incorporated into a previously validated finite element model of the human lumbar spine. Results suggest that the effects of increased ligament model fidelity on bone strain energy were moderate and the effects on disc pressure were slight, and do not justify a change in modelling strategy for most clinical applications. There were significant effects on the ligament stresses of the ligaments that were directly modified, suggesting that these phenomena should be included in FE models where ligament stresses are the desired metric.

A numerical study to determine the effect of ligament stiffness on kinematics of the lumbar spine during flexion

Background

There is a wide range of mechanical properties of spinal ligaments documented in literature. Due to the fact that ligaments contribute in stabilizing the spine by limiting excessive intersegmental motion, those properties are of particular interest for the implementation in musculoskeletal models. The aim of this study was to investigate the effect of varying ligament stiffness on the kinematic behaviour of the lumbar spine.

Methods

A musculoskeletal model with a detailed lumbar spine was modified according to fluoroscopic recordings and corresponding data files of three different subjects. For flexion, inverse dynamics analysis with a variation of the ligament stiffness matrix were conducted. The influence of several degrees of ligament stiffness on the lumbar spine model were investigated by tracking ligament forces, disc forces and resulting moments generated by the ligaments. Additionally, the kinematics of the motion segments were evaluated.

Results

An increase of ligament stiffness resulted in an increase of ligament and disc forces, whereas the relative change of disc force increased at a higher rate at the L4/L5 level (19 %) than at the L3/L4 (10 %) level in a fully flexed posture. The same behaviour applied to measured moments with 67 % and 45 %. As a consequence, the motion deflected to the lower levels of the lumbar spine and the lower discs had to resist an increase in loading.

Conclusions

Higher values of ligament stiffness over all lumbar levels could lead to a shift of the loading and the motion between segments to the lower lumbar levels. This could lead to an increased risk for the lower lumbar parts.

Transversely isotropic material characterization of the human anterior longitudinal ligament

The present work represents the first study to report transversely isotropic material parameters for the human anterior longitudinal ligament (ALL) in the thoraco-lumbar spine. Force-deformation data from multi-axial testing was collected from 30 cadaveric spine test specimens using an anisotropic quarter punch test technique. The experimental data was fit to a commonly used anisotropic soft tissue material model using an FEA system identification technique. The material model correlated well with the experimental response (R(2)≥0.98). The constitutive parameter values, as well as the nonlinear anisotropic stress-strain response of the ALL specimens are reported to facilitate application to biomechanical models (including finite element models) of the spine.