Biomechanical analysis of lumbar fusion with proximal interspinous process device implantation

Biomechanical investigation of a customized interspinous spacer system in the treatment of degenerative disc diseases: A finite element analysis

BACKGROUND

A novel interspinous fixation system based on anatomical parameters and incorporating transfacetopedicular screws, was developed to treat degenerative disc diseases. The biomechanical characteristics of the novel system were evaluated using finite element analysis in comparison to other classical interspinous spacers.

METHODS

The L1-S1 lumbar spine finite element models were surgically implanted with the novel system, Coflex and DIAM devices at the L4/L5 segment to assess the range of motion, the pression distribution of intervertebral disc, the peak stresses on the spinous process and implant during various motions.

FINDINGS

Range of motions of the L4/L5 surgical segment were reduced by 29.13%, 61.27%, 77.35%, 33.33%, and the peak stresses of intervertebral disc were decreased by 36.82%, 67.31%, 73.00%, 69.57% for the novel system in flexion, extension, lateral bending, and axial rotation when compared with the Coflex, and they were declined by 34.53%, 57.86%, 75.81%, 25.21%; 36.22%, 67.31%, 75.01%, 71.40% compared with DIAM. The maximum stresses of the spinous process were 29.93 MPa, 24.66 MPa, 14.45 MPa, 24.37 MPa in the novel system, and those of Coflex and DIAM were 165.3 MPa, 109 MPa, 84.79 MPa, 47.66 MPa and 52.59 MPa, 48.78 MPa, 50.27 MPa, 44.16 MPa during the same condition.

INTERPRETATION

Compared to other interspinous spacer devices, the novel interspinous fixation system demonstrated excellent stability, effectively distributing load on the intervertebral disc, and reducing the risk of spinous process fractures. The personalized design of the novel interspinous fixation system could be a viable option for treating degenerative disc diseases.

Determining a relative total lumbar range of motion to alleviate adjacent segment degeneration after transforaminal lumbar interbody fusion: a finite element analysis

BACKGROUND

A reduction in total lumbar range of motion (ROM) after lumbar fusion may offset the increase in intradiscal pressure (IDP) and facet joint force (FJF) caused by the abnormally increased ROM at adjacent segments. This study aimed to determine a relative total lumbar ROM rather than an ideal adjacent segment ROM to guide postoperative waist activities and further delay adjacent segment degeneration (ASD).

METHODS

An intact L1-S1 finite element model was constructed and validated. Based on this, a surgical model was created to allow the simulation of L4/5 transforaminal lumbar interbody fusion (TLIF). Under the maximum total L1-S1 ROM, the ROM, IDP, and FJF of each adjacent segment between the intact and TLIF models were compared to explore the biomechanical influence of lumbar fusion on adjacent segments. Subsequently, the functional relationship between total L1-S1 ROM and IDP or total L1-S1 ROM and FJF was fitted in the TLIF model to calculate the relative total L1-S1 ROMs without an increase in IDP and FJF.

RESULTS

Compared with those of the intact model, the ROM, IDP, and FJF of the adjacent segments in the TLIF model increased by 12.6-28.9%, 0.1-6.8%, and 0-134.2%, respectively. As the total L1-S1 ROM increased, the IDP and FJF of each adjacent segment increased by varying degrees. The relative total L1-S1 ROMs in the TLIF model were 11.03°, 12.50°, 12.14°, and 9.82° in flexion, extension, lateral bending, and axial rotation, respectively.

CONCLUSIONS

The relative total L1-S1 ROMs after TLIF were determined, which decreased by 19.6-29.3% compared to the preoperative ones. Guiding the patients to perform postoperative waist activities within these specific ROMs, an increase in the IDP and FJF of adjacent segments may be effectively offset, thereby alleviating ASD.

Prediction of the biomechanical behaviour of the lumbar spine under multi-axis whole-body vibration using a whole-body finite element model

Low back pain has been reported to have a high prevalence among occupational drivers. Whole-body vibration during the driving environment has been found to be a possible factor leading to low back pain. Vibration loads might lead to degeneration and herniation of the intervertebral disc, which would increase incidence of low back problems among drivers. Some previous studies have reported the effects of whole-body vibration on the human body, but studies on the internal dynamic responses of the lumbar spine under multi-axis vibration are limited. In this study, the internal biomechanical response of the intervertebral disc was extracted to investigate the biomechanical behaviour of the lumbar spine under a multi-axial vibration in a whole-body environment. A whole-body finite element model, including skin, soft tissues, the bone skeleton, internal organs and a detailed ligamentous lumbar spine, was used to provide a whole-body condition for analyses. The results showed that both vibrations close to vertical and fore-and-aft resonance frequencies would increase the transmission of vibrations in the intervertebral disc, and vertical vibration might have a greater effect on the lumbar spine than fore-and-aft vibration. The larger deformation of the posterior region of the intervertebral disc in a multi-axis vibration environment might contribute to the higher susceptibility of the posterior region of the intervertebral disc to injury. The findings of this study revealed the dynamic behaviours of the lumbar spine in multi-axis vehicle vibration conditions, and suggested that both vertical and fore-and-aft vibration should be considered for protecting the lumbar health of occupational drivers.

Efficacy and Safety of Lumbar Dynamic Stabilization Device Coflex for Lumbar Spinal Stenosis: A Systematic Review and Meta-analysis

BACKGROUND

This systematic review and meta-analysis were performed to investigate evidence for the comparison of lumbar dynamic stabilization device Coflex (Surgalign, Deerfield, IL) with posterior lumbar fusion for lumbar spinal stenosis).

METHODS

Relational databases were searched to October 2022. The main outcome measures included operation time, Japanese Orthopedic Association score (JOA), visual analog scale (VAS), Oswestry disability index (ODI), total complications, and adjacent segment degeneration (ASD). Statistical analysis was performed with Review Manager 5.3 (Cochrane Collaboration).

RESULTS

A total of 26 studies were included. The main results of this meta-analysis showed lumbar dynamic stabilization device Coflex had shorter operation time (mean difference [MD] -50.77 min, 95% CI -57.24 to -44.30, P < 0.00001), less intraoperative blood loss (MD -122.21 mL, 95% CI -129.68 to -94.74, P < 0.00001), and shorter hospital stays (MD -3.21 days, 95% CI -4.04 to -2.37, P < 0.00001). What's more, the JOA score and ODI score were higher in the Coflex group during early follow-up. Yet, there was no significant difference between the 2 groups with the extension of follow-up time. Moreover, the Coflex group had a lower VAS score than fusion treatment (P < 0.00001). Finally, the Coflex group had lower total complications rate (P = 0.03), lower ASD rate (P = 0.001), and higher range of motion (P < 0.00001), but there was no significant difference in reoperation rate and internal fixation problems rate.

CONCLUSIONS

Current evidence suggests that lumbar dynamic stabilization device Coflex is superior to posterior lumbar fusion in early follow-up. However, considering that the dynamic stabilization device group also has its limitations, these findings need to be further verified by multicenter, double-blind, and large-sample randomized controlled trials.

Biomechanical analysis of lumbar nonfusion dynamic stabilization using a pedicle screw-based dynamic stabilizer or an interspinous process spacer

This study aimed to investigate and compare the effects of two widely used nonfusion posterior dynamic stabilization (NPDS) devices, pedicle screw-based dynamic stabilizer (PSDS) and interspinous process spacer (IPS), on biomechanics of the implanted lumbar spine under static and vibration loadings. The finite element model of healthy human lumbosacral segment was modified to incorporate NPDS device insertion at L4-L5 segment. Bioflex and DIAM were used as PSDS-based and IPS-based NPDS devices, respectively. As a comparison, lumbar interbody fusion with rigid stabilization was also simulated at L4-L5. For static loading, segmental range of motion (ROM) of the models under moments of four physiological motions was computed using hybrid testing protocol. For vibration loading, resonant modes and dynamic stress of the models under vertical excitation were extracted through random response analysis. The results showed that compared with the rigid fusion model, ROM of the nonfusion models was higher at L4-L5 level but lower at adjacent levels (L1- L2, L2-L3, L3-L4, L5-S1). Compared with the Bioflex model, the DIAM model produced higher ROM at L4-L5 level but lower ROM at adjacent levels, especially under lateral bending and axial rotation; resonant frequency of the DIAM model was slightly lower; dynamic response of nucleus stress at L4-L5 level was slightly higher for the DIAM model, and the dynamic stress at adjacent levels was no obvious difference between the nonfusion models. This study reveals biomechanical differences between the Bioflex and DIAM systems, which may provide references for selecting surgical approaches in clinical practice.

Study on the process of intervertebral disc disease by the theory of continuum damage mechanics

BACKGROUND

Recently, more and more people suffer from low back pain triggered by lumbar degenerative disc disease. The mechanical factor is one of the most significant causes of disc degeneration. This study aims to explore the biomechanical responses of the intervertebral disc, and investigate the process of disc injury by the theory of continuum damage mechanics.

METHODS

A finite element model of the L4-L5 lumbar spine was developed and validated. The model not only considered changes in permeability coefficient with strain, but also included physiological factors such as osmotic pressure. Three loading conditions were simulated: (A) static loads, (B) vibration loads, (C) injury process.

FINDINGS

The simulation results revealed that the facet joints shared massive stresses of the intervertebral discs, and prevented excessive lumbar spine movement. However, their asymmetrical position may have led to degeneration. The von Mises stress and pore pressure of annulus fibrosus showed significantly different trends under static loads and vibration loads. The von Mises stress of nucleus pulposus was not sensitive to vibration loads, but its pore pressure was conspicuously influenced by vibration loads. The injury first appeared at the posterior centre, and then, it gradually expanded along the edge of the intervertebral disc. With an increase in the loading steps, the damage rate of the intervertebral disc increased logarithmically.

INTERPRETATION

The variation in the biomechanical performance of the intervertebral disc could be attributed to the periodic movement of internal fluids. This study might be helpful for understanding the mechanism of intervertebral disc degeneration.