Spine
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Somatosensory evoked potentials (SEPs) were recorded at the lumbar spine following stimulation of the tibial nerve (mixed-nerve SEP; MSEP), the sural nerve (specific nerve SEP; SSEP), and the skin corresponding to the L6 and S1 dermatomes (dermatomal field SEP; DSEP-L and DSEP-S) in the hog. To determine the sensitivity of these three SEPs to the single nerve root (S1 root) function, the effects of nerve roots lesioning were investigated. Cutting S1 nerve root reduced the peak-to-peak amplitude of MSEP by only 28% in comparison with baseline values. ⋯ When S1 nerve root was left intact and L5, L6, and S2 nerve roots were cut, the relative amplitudes of MSEP, SSEP, DSEP-L, and DSEP-S were decreased to 68%, 73%, 31%, and 74%, respectively. These results indicate that DSEP-S is as sensitive to the function of S1 nerve root as SSEP but the sensitivities of DSEP-S and SSEP are low in the hog. MSEP is shown unsuitable to monitor the single nerve root dysfunction.
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A modeling study was undertaken to determine the effects of flexion on the forces exerted by the lumbar back muscles. Twenty-nine fascicles of the lumbar multifidus and erector spinae were plotted onto tracings of radiographs of nine normal volunteers in the flexion position. Moment arms and force vectors of each fascicle were calculated. ⋯ However, there were major changes in shear forces, in particular a reversal from a net anterior to a net posterior shear force at the L5/S1 segment. Flexion causes substantial elongation of the back muscles, which must therefore reduce their maximum active tension. However, if increases in passive tension are considered it emerges that the compression forces and moments exerted by the back muscles in full flexion are not significantly different from those produced in the upright posture.
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Blue-collar and white-collar employees in the metal industry were studied for leisure time physical activity, smoking, the body mass index, stress symptoms, and low back disorders by questionnaire, interview, and clinical examination. Measurements were made three times at 5-year intervals. The initial sample of 902 was stratified for age group, sex, and occupational class. ⋯ In men, the mean exercise activity during the first 5-year follow-up was moderately inversely associated with the back symptoms and findings at the end of the follow-up, when the relevant morbidity score at the second examination, age, and occupational class were allowed for in multiple regression analysis. The effects persisted when data on smoking, the body mass index, and stress symptoms were added into the models. Strenuous activity predicted the change only in the clinical findings, and the association was reduced when the other lifestyle factors were accounted for.
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Thoracolumbar rotation was measured by a noninvasive method in 135 patients with ankylosing spondylitis. The mean of the total rotation from the level of the xiphisternum to S1 was 45.2 degrees, which is approximately half of that in healthy subjects measured by comparable methods. ⋯ Reproducibility of the method was good. Measurement of thoracolumbar rotation is seldom used in the assessment of ankylosing spondylitis, and merits further evaluation.
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Twenty-two adolescent patients with severe (more than 50%) slip were surgically treated. Eleven were reduced with Magerl/Dick transpedicular screw devices and fused posteriorly from L4 to S1, and 2 weeks later anteriorly L5-S1; the other 11 were fused in situ L4-S1 (6 patients) or L5-S1 (5 patients) using a circumferential (6 patients), anterior (4 patients) or posterolateral (1 patient) technique without instrumentation. The two groups were comparable as to age at operation, age at follow-up, follow-up time, and preoperative radiologic measurement of the slip, lumbosacral kyphosis, and clinical findings. ⋯ Reduction procedures were also associated with a higher number of complications and reoperations. No neurologic complications, however, occurred in the reduction group. Based on this study, in situ fusions are to be preferred in adolescents with severe spondylolisthesis.