Kazuhiko Ichihara

Gray Matter of the Bovine Cervical Spinal Cord is Mechanically More Rigid and Fragile than the White Matter

The gray matter of the cervical spinal cord has been thought to be equally or less rigid than the white matter. Based on this assumption, various studies have been conducted on the changes of stress distributions within the spinal cord under mechanical compression, although the mechanical properties of the white and gray matters had not been fully elucidated. The present study measured the mechanical properties of the white and gray matter of bovine spinal cords. For both the white and gray matter, the stress-strain curves had a nonlinear region, followed by a linear region, and then a region where the stresses plateaued before failure. In the nonlinear region, stress was not significantly different between the gray and white matter samples (strain approximately 0-10%), while stress and Youngs modulus in the gray matter was significantly higher than the white matter in the linear part of the curve. The gray matter ruptured at lower strains than the white matter. These findings demonstrated the gray matter is more rigid and fragile than the white matter, and the conventional assumption (i.e., the white matter is more rigid than the gray matter) is not correct. We then applied our data to computer simulations using the finite element method, and confirmed that simulations agreed with actual magnetic resonance imaging findings of the spinal cord under compression. In future computer simulations, including finite element method using our data, changes in stress and strain within the cervical spinal cord under compression would be clarified in more detail, and our findings would also help to elucidate the area which can easily receive histologic damage or which could have hemodynamic disorders under mechanical compression, as well as severity and location of biochemical and molecular biological changes.

Biomechanical study of cervical flexion myelopathy using a three-dimensional finite element method

OBJECT The goal of this study was to perform a biomechanical study of cervical flexion myelopathy (CFM) using a finite element method. METHODS A 3D finite element model of the spinal cord was established consisting of gray matter, white matter, and pia mater. After the application of semi-static compression, the model underwent anterior flexion to simulate CFM. The flexion angles used were 5 degrees and 10 degrees , and stress distributions inside the spinal cord were then evaluated. RESULTS Stresses on the spinal cord were very low under semi-static compression but increased after 5 degrees of flexion was applied. Stresses were concentrated in the gray matter, especially the anterior and posterior horns. The stresses became much higher after application of 10 degrees of flexion and were observed in the gray matter, posterior funiculus, and a portion of the lateral funiculus. CONCLUSIONS The 5 degrees model was considered to represent the mild type of CFM. This type corresponds to the cases described in the original report by Hirayama and colleagues. The main symptom of this type of CFM is muscle atrophy and weakness caused by the lesion of the anterior horn. The 10 degrees model was considered to represent a severe type of CFM and was associated with lesions in the posterior fand lateral funiculi. This type of CFM corresponds to the more recently reported clinical cases with combined long tract signs and sensory disturbance.

The treatment of far-out foraminal stenosis below a lumbosacral transitional vertebra: a report of two cases.

Far-out foraminal stenosis with radiculopathy caused by bony spur formation secondary to anomalous articulation between the transverse process and the sacral ala is rarely reported. We report two cases of unilateral far-out foraminal entrapment of the L5 spinal nerve below a transitional vertebra, with a review of the literature. The objective of this work was to describe the management of a rare far-out foraminal stenosis below a transitional vertebra and to evaluate the surgical and conservative procedures and results. In a previous article, decompression was performed through an anterior approach. However, we report no difficulty with decompression using a posterior approach for one patient. The diagnosis was confirmed with computed tomography, magnetic resonance imaging, and selective radiculography. First, selective nerve root blocks were performed in two cases for the purpose of nonoperative treatment. After failure of conservative treatment with selective nerve root block, one patient underwent posterior decompression by resection of the bony spur using a posterior approach. One patient obtained good relief of radicular pain with only selective nerve root block. The other patient obtained good relief of radicular pain after posterior decompression was performed. Posterior decompression through the posterior approach is an easy, safe, and useful treatment for radicular pain caused by an L5 nerve far-out foraminal stenosis below a transitional vertebra when conservative treatments have failed to obtain good relief of radicular pain.

Biomechanical study of the effect of degree of static compression of the spinal cord in ossification of the posterior longitudinal ligament.

OBJECT The authors evaluated the biomechanical effect of 3 different degrees of static compression in a model of the spinal cord in order to investigate the effect of cord compression in patients with ossification of the posterior longitudinal ligament (OPLL). METHODS A 3D finite element spinal cord model consisting of gray matter, white matter, and pia mater was established. As a simulation of OPLL-induced compression, a rigid plate compressed the anterior surface of the cord. The degrees of compression were 10, 20, and 40% of the anteroposterior (AP) diameter of the cord. The cord was supported from behind by the rigid body along its the posterior border, simulating the lamina. Stress distributions inside of the cord were evaluated. RESULTS The stresses on the cord were very low under 10% compression. At 20% compression, the stresses on the cord increased very slightly. At 40% compression, the stresses on the cord became much higher than with 20% compression, and high stress distributions were observed in gray matter and the lateral and posterior funiculus. The stresses on the compressed layers were much higher than those on the uncompressed layer. CONCLUSIONS The stress distributions at 10 and 20% compression of the AP diameter of the spinal cord were very low. The stress distribution at 40% compression was much higher. The authors conclude that a critical point may exist between 20 and 40% compression of the AP diameter of the cord such that when the degree of the compression exceeds this point, the stress distribution becomes much higher, and that this may contribute to myelopathy.

Age-related change of postoperative pain location after Nuss procedure for pectus excavatum

OBJECTIVE The present study aims to evaluate age-related change of postoperative pain after the Nuss procedure by referring to clinical cases, and to elucidate the biomechanical aetiology of the change by using the finite element method. METHODS Twelve paediatric patients (paediatric group: 9.4+/-2.3 years old) and 13 adult patients (adult group: 26.3+/-5.5 years old) who received the Nuss procedure for pectus excavatum were included in the study. On the second postoperative day, the patients were asked to indicate regions on the thorax where they felt the greatest pain. The locations of these regions were compared between the two groups. In addition, stress-distribution patterns were examined using finite element models produced by simulating the thoraces of the patients. The stress-distribution patterns were compared between the two groups. RESULTS The patients of the paediatric group and adult group tend to have pain on the anterior and posterior regions of the thorax, respectively. The finite element study revealed that paediatric thoraces and adult thoraces develop intensified stresses in the anterior region and the posterior region, respectively. CONCLUSION Postoperative pain tends to occur in the anterior part of the thorax for paediatric patients and in the posterior part of the thorax for adult patients, reflecting the stress distributions of these two distinct patient populations.

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.

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.

Follow up studies of Unilateral Total Hip Arthroplasty in Bilateral Osteoartheritis

We report the follow-up results in 22 cases of unilateral total hip arthroplasty in patihents with bilateral osteoarthritis.1. Pain of sixteen unoperated hips (73%) improved after one year of implantation2. Radiological findings improved in 14 hips (64%) with recovery of hip joint space.3. Patients with bilateral osteoartheritis improved. and radiological roof osteophyte and end stage osteoartheritis