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 Young's 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.

Object. The authors have previously investigated the mechanical properties of the white and gray matter in the bovine cervical spinal cord, demonstrating that the gray matter is more rigid, although more fragile, than the white matter. In the present study they conducted additional tensile tests on the bovine cervical spinal cord by changing strain levels and strain rates applied to the white and gray matter. Methods. Based on their testing, the authors found the following: 1) Stress within the spinal cord relaxes over time. 2) Intracord stress is related to the strain rates or levels. The finite element method was used to compute the stress distribution within the spinal cord under three compressive loading conditions. Results from the computations showed a different stress distribution in the white and gray matter, where the distribution of stress varied with strain rate, compression volume, and the position of compression. Conclusions. These differences in mechanical properties between the white and gray matter constitute different mechanisms contributing to the development of tissue damage and clinical symptoms.

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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° and 10°, 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° 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° of flexion and were observed in the gray matter, posterior funiculus, and a portion of the lateral funiculus. Conclusions The 5° 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° 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.

Objective-To assess the influence of environmental exposure to cadmium (Cd) on long term outcome of inhabitants living in an area polluted by Cd. Methods-A follow up study for 15 years (from 1974-5 to 1991) was carried out on 2408 inhabitants (amounting to 95% of the target population, 1079 men and 1329 women) of the Kakehashi River basin in Ishikawa Prefecture, Japan. These inhabitants had been the subjects of the health impact survey in 1974-5 to evaluate (by measurement of urinary retinol binding protein (RBP)) renal dysfunction induced by Cd. Analysis of mortality was performed by dividing subjects into a urinary RBP positive ( > 4 mg/1) group and RBP negative (<4 mg/l) group. Results-After adjustment for age with Cox's proportional hazard model, RBP > 4 mg/l showed a significant relation to mortality in both sexes. At this time, the mortality risk ratio of the RBP positive to negative group was 1-71 in the men and 1*42 in the women. When the SMRs according to causes of deaths in the RBP positive group were compared with those of the RBP negative group or the overall Japanese population increases of SMR for cardiovascular diseases, especially heart failure, and renal diseases were found in both sexes. Conclusion-These results suggest that the prognosis of the exposed inhabitants with renal tubular dysfunction is unfavourable, and these increases of mortality are due to heart failure and renal diseases. (Occup Environ Med 1995;52:181-184)