Development and validation of lumbar spine finite element model

Development of a spinopelvic complex finite element model for quantitative analysis of the biomechanical response of patients with degenerative spondylolisthesis

Research on degenerative spondylolisthesis (DS) has focused primarily on the biomechanical responses of pathological segments, with few studies involving muscle modelling in simulated analysis, leading to an emphasis on the back muscles in physical therapy, neglecting the ventral muscles. The purpose of this study was to quantitatively analyse the biomechanical response of the spinopelvic complex and surrounding muscle groups in DS patients using integrative modelling. The findings may aid in the development of more comprehensive rehabilitation strategies for DS patients. Two new finite element spinopelvic complex models with detailed muscles for normal spine and DS spine (L4 forwards slippage) modelling were established and validated at multiple levels. Then, the spinopelvic position parameters including peak stress of the lumbar isthmic-cortical bone, intervertebral discs, and facet joints; peak strain of the ligaments; peak force of the muscles; and percentage difference in the range of motion were analysed and compared under flexion-extension (F-E), lateral bending (LB), and axial rotation (AR) loading conditions between the two models. Compared with the normal spine model, the DS spine model exhibited greater stress and strain in adjacent biological tissues. Stress at the L4/5 disc and facet joints under AR and LB conditions was approximately 6.6 times greater in the DS spine model than in the normal model, the posterior longitudinal ligament peak strain in the normal model was 1/10 of that in the DS model, and more high-stress areas were found in the DS model, with stress notably transferring forwards. Additionally, compared with the normal spine model, the DS model exhibited greater muscle tensile forces in the lumbosacral muscle groups during F-E and LB motions. The psoas muscle in the DS model was subjected to 23.2% greater tensile force than that in the normal model. These findings indicated that L4 anterior slippage and changes in lumbosacral-pelvic alignment affect the biomechanical response of muscles. In summary, the present work demonstrated a certain level of accuracy and validity of our models as well as the differences between the models. Alterations in spondylolisthesis and the accompanying overall imbalance in the spinopelvic complex result in increased loading response levels of the functional spinal units in DS patients, creating a vicious cycle that exacerbates the imbalance in the lumbosacral region. Therefore, clinicians are encouraged to propose specific exercises for the ventral muscles, such as the psoas group, to address spinopelvic imbalance and halt the progression of DS.

Biomechanical Characteristics of First Coronal Reverse Vertebrae in Lenke Type V Adolescent Idiopathic Scoliosis: A Study Using Finite Element Analysis

OBJECTIVE

Whether first coronal reverse vertebrae (FCRV) can directly cause biomechanical changes in adjacent segments remains unclear. The objective of this study was to explore the biomechanical changes in adjacent discs of the FCRV to better understand the stress distribution of adolescent idiopathic scoliosis (AIS).

METHODS

According to the plain CT scan data of T8-T10 segment of an AIS patient, T9 was the FCRV, and a three-dimensional FE model was established accurately. The T8-T9 segment disc was defined as the adjacent upper disc (UD), axial section as half of the upper disc (HUD). Similarly, T9-T10 segment disc was the adjacent lower disc (LD), axial section as half of the lower disc (HLD). The biomechanical changes in adjacent discs of the FCRV under different loads were assessed.

RESULTS

The maximum Von-Mises stress values of the LD were greater under various loads than those of the HLD, UD, and HUD. The average stress on the LD was greater than that of the other discs under the left lateral bending (LLB) or right lateral bending (RLB) load. It was noted that the concave side of the LD was subjected to greater stress under the neutral standing or LLB load compared with convex side. Additionally, the concave side of the LD was subjected to greater stress under the LLB or RLB load compared with that of other discs. Interestingly, the same trends were observed for the convex side of the LD.

CONCLUSIONS

FCRV caused LD to take on greater stress magnitudes. The stress showed a trend of local concentration, which was in the concave side of the scoliosis. These findings could contribute to further treatment planning for the patient and aid physicians' management decision-making.

Quantitative Analysis of Stress-Stretch Curves in Canine Lumbar Vertebrae Using Modified Logistic Functions

BACKGROUND

The mechanical characteristics of bone are crucial for comprehending its functionality and response to different load conditions, which are essential for advancing medical treatments, implants, and prosthetics. By employing mathematical modeling to analyze the mechanical properties of bone, we can assess stress and deformation under both normal and abnormal conditions. This analysis offers valuable perspectives on potential fracture risks, the effects of diseases, and the effectiveness of various treatments. Therefore, researchers are attempting to find an adequate mathematical description of the mechanical properties of bone.

METHODS

Experimental stress-stretch external loading curves were obtained through investigations of canine vertebrae. The obtained experimental curves were fitted using the SciPy Python library with a slightly modified logistic function (logistic function plus additional const).

RESULTS

The resulting coefficient of determination R2 (R squared) for most curves was near 0.999, indicating that an appropriate fitting function was selected for the description of the experimental stress-stretch curves.

CONCLUSIONS

The stress-stretch behavior of canine vertebrae can be described using a logistic function modified by adding additional parameters for the most accurate fitting results.

Mechanical response of human thoracic spine ligaments under quasi-static loading: An experimental study

PURPOSE

This study aimed to investigate the geometrical and mechanical properties of human thoracic spine ligaments subjected to uniaxial quasi-static tensile test.

METHODS

Four human thoracic spines, obtained through a body donation program, were utilized for the study. The anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), capsular ligament (CL), ligamenta flava (LF), and the interspinous ligament and supraspinous ligament complex (ISL + SSL), were investigated. The samples underwent specimen preparation, including dissection, cleaning, and reinforcement, before being immersed in epoxy resin. Uniaxial tensile tests were performed using a custom-designed mechanical testing machine equipped with an environmental chamber (T = 36.6 °C; humidity 95%). Then, the obtained tensile curves were averaged preserving the characteristic regions of typical ligaments response.

RESULTS

Geometrical and mechanical properties, such as initial length and width, failure load, and failure elongation, were measured. Analysis of variance (ANOVA) revealed significant differences among the ligaments for all investigated parameters. Pairwise comparisons using Tukey's post-hoc test indicated differences in initial length and width. ALL and PLL exhibited higher failure forces compared to CL and LF. ALL and ISL + SSL demonstrated biggest failure elongation. Comparisons with other studies showed variations in initial length, failure force, and failure elongation across different ligaments. The subsystem (Th1 - Th6 and Th7 - Th12) analysis revealed increases in initial length, width, failure force, and elongation for certain ligaments.

CONCLUSIONS

Variations of both the geometric and mechanical properties of the ligaments were noticed, highlighting their unique characteristics and response to tensile force. Presented results extend very limited experimental data base of thoracic spine ligaments existing in the literature. The obtained geometrical and mechanical properties can help in the development of more precise human body models (HBMs).

The effect of stretching exercises on the mobility of the spine in the sagittal plane in people using digital devices – preliminary observations

Introduction. Digital devices and a sedentary lifestyle pose significant health risks in today’s society, further exacerbated by the regular adoption of incorrect posture. Prolonged adoption of an incorrect posture can result in pain and impaired spinal mobility. Aim of the study. The study aims to evaluate the impact of stretching exercises on improving cervical, thoracic and lumbar spine mobility in the sagittal plane. Furthermore, it sought to examine the potential correlation between the occurrence of pain and the duration of digital equipment usage. Study materials and methodology. The study was conducted on a sample group of 22 individuals aged 18 to 21 (20.11 ± 1.56) years. Linear measurements, including the Schober and Otto-Wurm tests, were used to examine spinal mobility in the sagittal plane. The subjects were given a 10-day programme comprising six stretching exercises to perform autonomously daily. After ten days, line measurements were retaken. Results. Significant statistical values were observed for spinal ranges of motion in the sagittal plane; no statistically significant value was obtained for the incidence of pain and the duration of use of digital devices. Conclusions. The subjects demonstrated improvement in cervical, thoracic, and lumbar spine mobility in the sagittal plane following the implementation of stretching exercises. Additionally, a decrease in spinal pain was observed.