Reduction in Disk and Fiber Stresses by Axial Distraction is Higher in Cervical Disk With Fibers Oriented Toward the Vertical Rather Than Horizontal Plane: A Finite Element Model Analysis

Proposal and validation of polyconvex strain-energy function for biological soft tissues

BACKGROUND

Mechanical simulations for biological tissues are effective technology for development of medical equipment, because it can be used to evaluate mechanical influences on the tissues. For such simulations, mechanical properties of biological tissues are required. For most biological soft tissues, stress tends to increase monotonically as strain increases.

OBJECTIVE

Proposal of a strain-energy function that can guarantee monotonically increasing trend of biological soft tissue stress-strain relationships and applicability confirmation of the proposed function for biological soft tissues.

METHOD

Based on convexity of invariants, a polyconvex strain-energy function that can reproduce monotonically increasing trend was derived. In addition, to confirm its applicability, curve-fitting of the function to stress-strain relationships of several biological soft tissues was performed.

RESULTS

A function depending on the first invariant alone was derived. The derived function does not provide such inappropriate negative stress in the tensile region provided by several conventional strain-energy functions.

CONCLUSIONS

The derived function can reproduce the monotonically increasing trend and is proposed as an appropriate function for biological soft tissues. In addition, as is well-known for functions depending the first invariant alone, uniaxial-compression and equibiaxial-tension of several biological soft tissues can be approximated by curve-fitting to uniaxial-tension alone using the proposed function.

A Finite Element Analysis of Stress Distribution and Disk Displacement in Response to Lumbar Rotation Manipulation in the Sitting and Side-Lying Positions

OBJECTIVE

This study aimed to investigate stress distribution and disk displacement in healthy and degenerated intervertebral disks during simulated lumbar rotation manipulation (LRM) in the sitting and side-lying positions.

METHODS

Three-dimensional (3D) finite element models of healthy, mildly degenerated and moderately degenerated L4/5 spinal units were reconstructed. Lumbar rotation manipulation in the sitting and side-lying positions were simulated, and alterations in stress distribution and disk displacement in the lumbar disks were observed.

RESULTS

The application of LRM in the sitting or side-lying position resulted in a similar stress distribution in healthy, mildly degenerated, and moderately degenerated disks. Stress was concentrated at the anterior right side of the annulus. In all disks, intradiskal pressure (IDP) and maximum von Mises stress were higher during LRM in the sitting position than during LRM in the side-lying position. During these manipulations, Intradiskal pressure and stress in the annulus of moderately degenerated disks were higher than in mildly degenerated disks. Displacement was most obvious in healthy disks.

CONCLUSIONS

Mildly and moderately degenerated lumbar disks were subject to higher stress during LRM in the sitting position than during LRM in the side-lying position. Intradiskal pressure and the maximum von Mises stress in the annulus of moderately degenerated disks increased, suggesting the need for caution when treating patients with moderately compromised disks. Although our results are in accordance with previously published data, they are simulated and preliminary and do not necessarily replicate the clinical condition.

The effects of neural mobilization on cervical radiculopathy patients' pain, disability, ROM, and deep flexor endurance

BACKGROUND

Cervical radiculopathy (CR) is a disease of the cervical spine and a space-occupying lesion that occurs because of pathological problems with cervical nerve roots. Nerve root injury to produce functional disability.

OBJECTIVE

The purpose of this study was to examine the effects of neural mobilization with manual cervical traction (NMCT) compared with manual cervical traction (MCT) on pain, functional disability, muscle endurance, and range of motion (ROM) in individuals with CR patients.

METHODS

A blinded randomized clinical trial was conducted. Thirty CR patients were divided into two groups - those who received NMCT and those who received MCT. The intervention was applied three times per week for eight weeks. It was measured in order to determine the pain and functional disability in patients with CR. The numeric pain rating scale (NPRS), neck disability index (NDI), ROM, and deep flexor endurance of patients were measured prior to the experiment, four weeks, and eight weeks after the experiment to compare the time points. A repeated-measures analysis of variance was used to compare differences within each group prior to the experiment. And Bonferroni test was performed to examine the significance of each time point.

RESULTS

There were significant differences within each group prior to the intervention, four weeks after the intervention, and eight weeks after the intervention in NPRS, NDI, ROM, and deep flexor endurance (P< 0.05). NPRS and NDI more decreased, and, ROM and deep flexor endurance increased in the NMCT group than the MCT group (P< 0.05).

CONCLUSIONS

These results suggest that the NMCT can pain relief, recovery from neck disability, ROM, and deep flexor endurance for patients with CR.

Real-time monitoring of stresses and displacements in cervical nuclei pulposi during cervical spine manipulation: a finite element model analysis

OBJECTIVE

The objective of this study was to research the distribution of stresses and displacements in cervical nuclei pulposi during simulated cervical spine manipulation (CSM).

METHODS

A 3-dimensional finite element model of C3/4~C6/7 was established. The detailed mechanical parameters of CSM were analyzed and simulated. During the process, the changes in stresses and displacements of cervical nuclei pulposi within the model were displayed simultaneously and dynamically.

RESULTS

Cervical spine manipulation with right rotation was targeted at the C4 spinous process of the model. During traction, levels of stresses and displacements of the nuclei pulposi exhibited an initial decrease followed by an increase. The major stresses and displacements affected the C3/4 nucleus pulposus during rotation in CSM, when its morphology gradually changed from circular to elliptical. The highest stress (48.53 kPa) occurred at its right superior edge, on rotating 40° to the right. It protruded toward the right superior, creating a gap in its left inferior aspect. The highest displacement, also at 40° right, occurred at its left superior edge and measured 0.7966 mm. Dimensions of stresses and displacements reduced quickly on rapid return to neutral position.

CONCLUSION

The morphology of the C3/4 nucleus pulposus changed during CSM with right rotation, and it created a gap in its left inferior aspect. Biomechanically, it is more safe and rational to rotate toward the healthy side than the prolapsed side of the intervertebral disk during CSM. Upon ensuring due safety, the closer the application force is to the diseased intervertebral disk, the better is the effect of CSM.