Junji Ohgi

Biomechanical simulation of thorax deformation using finite element approach.

BackgroundThe biomechanical simulation of the human respiratory system is expected to be a useful tool for the diagnosis and treatment of respiratory diseases. Because the deformation of the thorax significantly influences airflow in the lungs, we focused on simulating the thorax deformation by introducing contraction of the intercostal muscles and diaphragm, which are the main muscles responsible for the thorax deformation during breathing.MethodsWe constructed a finite element model of the thorax, including the rib cage, intercostal muscles, and diaphragm. To reproduce the muscle contractions, we introduced the Hill-type transversely isotropic hyperelastic continuum skeletal muscle model, which allows the intercostal muscles and diaphragm to contract along the direction of the fibres with clinically measurable muscle activation and active force–length relationship. The anatomical fibre orientations of the intercostal muscles and diaphragm were introduced.ResultsThorax deformation consists of movements of the ribs and diaphragm. By activating muscles, we were able to reproduce the pump-handle and bucket-handle motions for the ribs and the clinically observed motion for the diaphragm. In order to confirm the effectiveness of this approach, we simulated the thorax deformation during normal quiet breathing and compared the results with four-dimensional computed tomography (4D-CT) images for verification.ConclusionsThorax deformation can be simulated by modelling the respiratory muscles according to continuum mechanics and by introducing muscle contractions. The reproduction of representative motions of the ribs and diaphragm and the comparison of the thorax deformations during normal quiet breathing with 4D-CT images demonstrated the effectiveness of the proposed approach. This work may provide a platform for establishing a computational mechanics model of the human respiratory system.

Mechanical properties of nerve roots and rami radiculares isolated from fresh pig spinal cords

No reports have described experiments designed to determine the strength characteristics of spinal nerve roots and rami radiculares for the purpose of explaining the complexity of symptoms of medullary cone lesions and cauda equina syndrome. In this study, to explain the pathogenesis of cauda equina syndrome, monoaxial tensile tests were performed to determine the strength characteristics of spinal nerve roots and rami radiculares, and analysis was conducted to evaluate the stress-strain relationship and strength characteristics. Using the same tensile test device, the nerve root and ramus radiculares isolated from the spinal cords of pigs were subjected to the tensile test and stress relaxation test at load strain rates of 0.1, 1, 10, and 100 s -1 under identical settings. The tensile strength of the nerve root was not rate dependent, while the ramus radiculares tensile strength tended to decrease as the strain rate increased. These findings provide important insights into cauda equina symptoms, radiculopathy, and clinical symptoms of the medullary cone.

Cervical ossification of the posterior longitudinal ligament: factors affecting the effect of posterior decompression

Objective: Decompression procedures for cervical myelopathy of ossification of the posterior longitudinal ligament (OPLL) are anterior decompression with fusion, laminoplasty, and posterior decompression with fusion. Preoperative and postoperative stress analyses were performed for compression from hill-shaped cervical OPLL using 3-dimensional finite element method (FEM) spinal cord models. Methods: Three FEM models of vertebral arch, OPLL, and spinal cord were used to develop preoperative compression models of the spinal cord to which 10%, 20%, and 30% compression was applied; a posterior compression with fusion model of the posteriorly shifted vertebral arch; an advanced kyphosis model following posterior decompression with the spinal cord stretched in the kyphotic direction; and a combined model of advanced kyphosis following posterior decompression and intervertebral mobility. The combined model had discontinuity in the middle of OPLL, assuming the presence of residual intervertebral mobility at the level of maximum cord compression, and the spinal cord was mobile according to flexion of vertebral bodies by 5°, 10°, and 15°. Results: In the preoperative compression model, intraspinal stress increased as compression increased. In the posterior decompression with fusion model, intraspinal stress decreased, but partially persisted under 30% compression. In the advanced kyphosis model, intraspinal stress increased again. As anterior compression was higher, the stress increased more. In the advanced kyphosis  + intervertebral mobility model, intraspinal stress increased more than in the only advanced kyphosis model following decompression. Intraspinal stress increased more as intervertebral mobility increased. Conclusion: In high residual compression or instability after posterior decompression, anterior decompression with fusion or posterior decompression with instrumented fusion should be considered.

Finite element analysis of compression fractures at the thoracolumbar junction using models constructed from medical images

Vertebral fractures commonly occur at the thoracolumbar junction. These fractures can be treated with mild residual deformity in many cases, but are reportedly associated with increased risk of secondary vertebral fractures. In the present study, a three-dimensional (3D) whole spine model was constructed using the finite element method to explore the mechanism of development of compression fractures. The 3D model of the whole spine, from the cervical spine to the pelvis, was constructed from computed tomography (CT) images of an adult male. Using a normal spine model and spine models with compression fractures at the T11, T12 or L1 vertebrae, the distribution of strain was analyzed in the vertebrae after load application. The normal spine model demonstrated greater strain around the thoracolumbar junction and the middle thoracic spine, while the compression fracture models indicated focused strain at the fracture site and adjacent vertebrae. Increased load time resulted in the extension of the strain region up to the middle thoracic spine. The present findings, that secondary vertebral fractures commonly occur around the fracture site, and may also affect the thoracic vertebrae, are consistent with previous clinical and experimental results. These results suggest that follow-up examinations of compression fractures at the thoracolumbar junction should include the thoracic spine and adjacent vertebrae. The current data also demonstrate that models created from CT images can be used for various analyses.

Effect of Intercostal Muscle Contraction on Rib Motion in Humans Studied by Finite Element Analysis

The effect of intercostal muscle contraction on generating rib motion has been investigated for a long time and is still controversial in physiology. This may be because of the complicated structure of the rib cage, making direct prediction of the relationship between intercostal muscle force and rib movement impossible. Finite element analysis is a useful tool that is good at solving complex structural mechanic problems. In this study, we individually activated the intercostal muscle groups from the dorsal to ventral portions and obtained five different rib motions classified based on rib moving directions. We found that the ribs cannot only rigidly rotate around the spinal joint but also be deformed, particularly around the relatively soft costal cartilages, where the moment of muscle force for the rigid rotation is small. Although the intercostal muscles near the costal cartilages cannot generate a large moment to rotate the ribs, the muscles may still have a potential to deform the costal cartilages and contribute to the expansion and contraction of the rib cage based on the force-length relationship. Our results also indicated that this potential is matched well with the special shape of the costal cartilages, which become progressively oblique in the caudal direction. Compared with the traditional explanation of rib motion, by additionally considering the effect from the tissue deformation, we found that the special structure of the ventral portion of the human rib cage could be of mechanical benefit to the intercostal muscles, generating inspiratory and expiratory rib motions. NEW & NOTEWORTHY Compared with the traditional explanation of rib motion, additionally considering the effect from tissue deformation helps us understand the special structure of the ventral portion of the human rib cage, such that the costal cartilages progressively become oblique and the costochondral junction angles gradually change into nearly right angles from the upper to lower ribs, which could be of mechanical benefit to the intercostal muscles in the ventral portion, generating inspiratory and expiratory rib motions.

Age‑related changes of the spinal cord: A biomechanical study

Although it is known that aging plays an important role in the incidence and progression of cervical spondylotic myelopathy (CSM), the underlying mechanism is unclear. Studies that used fresh bovine cervical spinal cord report the gray matter of the cervical spinal cord as being more rigid and fragile than the white matter. However, there are no reports regarding the association between aging an tensile and Finite Element Method (FEM). Therefore, FEM was used based on the data pertaining to the mechanical features of older bovine cervical spinal cord to explain the pathogenesis of CSM in elderly patients. Tensile tests were conducted for white and gray matter separately in young and old bovine cervical spinal cords, and compared with their respective mechanical features. Based on the data obtained, FEM analysis was further performed, which included static and dynamic factors to describe the internal stress distribution changes of the spinal cord. These results demonstrated that the mechanical strength of young bovine spinal cords is different from that of old bovine spinal cords. The gray matter of the older spinal cord was significantly softer and more resistant to rupture compared with that of younger spinal cords (P<0.05). Among the old, although the gray matter was more fragile than the white matter, it was similar to the white matter in terms of its rigidity (P<0.05). The in vitro data were subjected to three compression patterns. The FEM analysis demonstrated that the stress level rises higher in the old spinal cords in response to similar compression, when compared with young spinal cords. These results demonstrate that in analyzing the response of the spinal cord to compression, the age of patients is an important factor to be considered, in addition to the degree of compression, compression speed and parts of the spinal cord compression factor.

Analysis of stress application at the thoracolumbar junction and influence of vertebral body collapse on the spinal cord and cauda equina

The thoracolumbar junction comprises the spinal cord, nerve roots and the cauda equina, exhibiting unique anatomical features that may give rise to a diverse array of symptoms under conditions of injury, thus complicating the diagnosis of compressive disorders. The present study aimed to examine varying degrees and forms of compression at this level of the spinal cord using a two-dimensional model to calculate the relationship of these variables to injury. The degree of compression was expressed as a percentage of the spinal canal that was occupied. Results were compared with findings from clinical observations to assess the validity of the model. Analysis revealed that higher levels of compression/spinal canal occupation are associated with the presence of neurological symptoms. This finding was consistent with clinical data. Results of the present analysis warrant further research involving evaluation of compression with respect to other parameters, such as blood flow, as well as more anatomically accurate three-dimensional analysis.

Biomechanical analysis of brachial plexus injury: Availability of three-dimensional finite element model of the brachial plexus

Adult brachial plexus injuries frequently lead to significant and permanent physical disabilities. Investigating the mechanism of the injury using biomechanical approaches may lead to further knowledge with regard to preventing brachial plexus injuries. However, there are no reports of biomechanical studies of brachial plexus injuries till date. Therefore, the present study used a complex three-dimensional finite element model (3D-FEM) of the brachial plexus to analyze the mechanism of brachial plexus injury and to assess the validity of the model. A complex 3D-FEM of the spinal column, dura mater, spinal nerve root, brachial plexus, rib bone and cartilage, clavicle, scapula, and humerus were conducted. Stress was applied to the model based on the mechanisms of clinically reported brachial plexus injuries: Retroflexion of the cervical, lateroflexion of the cervical, rotation of the cervical, and abduction of the upper limb. The present study analyzed the distribution and strength of strain applied to the brachial plexus during each motion. When the cervical was retroflexed or lateroflexed, the strain was focused on the C5 nerve root and the upper trunk of the brachial plexus. When the upper limb was abducted, strain was focused on the C7 and C8 nerve roots and the lower trunk of the brachial plexus. The results of brachial plexus injury mechanism corresponded with clinical findings that demonstrated the validity of this model. The results of the present study hypothesized that the model has a future potential for analyzing pathological conditions of brachial plexus injuries and other injuries or diseases, including that of spine and spinal nerve root.

Simulation of Cervical Cord Compression Using Finite Element Method (FEM)

Cervical myelopathy results in loss of nerves functions along the spinal cord below the damage area as it is the result of spinal cord compression which nowadays always occur during traffic accidents. Patients with cervical myelopathy do not necessarily share the same symptoms. These vary according to the degree of cervical cord compression and cross sectional shape at every segment of cervical cord which caused difficulties in diagnosis. In this study, two dimension model of every cervical cord segment were built. Then, differences of compression results in every segment were verified. After that, to verify the effects of compression to other segments, three dimensions model of cervical cord model is built. From this study, we can see that cervical cord with flat shaped gray matter have higher stress distribution than cervical cord with hill shaped grey matter. Other than that, the injury start occurred in ventral column of white matter instead of gray matter during early injury stage.

Study on Nondestructive Tomographic Visualization of Plane-Woven Fiber-Reinforced Rubber Using Optical Coherence Straingraphy

Authors proposed Optical Coherence Straingraphy (OCS), which could visualize micromechanical information, e.g. strain, tomographically and non-destructively. This method can execute the speckle deformation analysis based on cross-correlation technique of synthetic images obtained before and after loading by Optical Coherence Tomography. In this study, applying OCS to composite materials, e.g. plain-woven fiber-reinforced rubber, the experimental feasibility study was carried out, compared with numerical simulated results by image-based FEM. Consequently, OCS could discover the strain concentration in the vicinity of the intersection of orthogonally oriented fiber bundles. It was confirmed that tomographic strain distribution had qualitative agreement with the simulated one. Therefore, OCS was verified to provide mechanical properties non-destructively as internal strain distribution at the micro scale resolution.Copyright