Spine
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To enhance understanding of the biomechanical role of the intervertebral disc, the compressive properties and biochemical composition of nondegenerate samples of anulus fibrosus were determined as a function of radial position, region, and level. Because of the large swelling propensity of this tissue, a method was developed to test excised specimens while maintaining their in situ geometry and hydration. ⋯ The findings indicate that the anulus fibrosus is inhomogeneous, with regional and radial variations in both material properties and biochemical composition. The results of this study suggest that both structural and compositional factors may determine the mechanical behavior.
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Comparative Study
L4-5 isthmic spondylolisthesis. A biomechanical analysis comparing stability in L4-5 and L5-S1 isthmic spondylolisthesis.
The authors have previously reported that the L4-5 isthmic spondylolisthesis lesion often progresses more than the L5-S1 lesion in adult patients. This biomechanical study compares the in vitro stability of the L4-5 isthmic spondylolisthesis lesion compared with the L5-S1 isthmic lesion. The authors also analyzed the role of the L5 iliolumbar ligament as a contributing factor to stability. ⋯ The iliolumbar ligament did not appear to contribute to these differences because there was no significant change in the L5-S1 kinematics after its transection. These results support the hypothesis that L4-5 pars defects are more unstable than L5-S1 lesions. The iliolumbar ligament could not be implicated as the major contributing factor in these differences.
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Iatrogenic pseudomeningocele formation after lumbar or cervical spine surgery is a well-described complication. Two unusual cases of transdural nerve root herniation with subsequent entrapment in the intervertebral space after lumbar disc surgery are presented. The reasons for this rare complication and its treatment are discussed.
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The incidence of sciatic pain among 25-49 year-old men in three different types of work: machine operating, dynamic physical work (construction carpenters), and office work was assessed prospectively. Postal questionnaires both at the beginning and the end of the 3-year follow-up were answered by 1149 men who at baseline had no history of sciatic pain. ⋯ Previous history of severe lumbago or other low-back pain increased the risk fourfold. Frequent physical exercise and smoking were of borderline significance as predictors.
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Magnetic resonance imaging was used to study the effect of different curvatures in the lumbar spine on lever arm lengths of the erector spinae musculature. Eleven subjects were instructed to simulate static lifts while lying supine in a magnetic resonance camera with the lumbar spine either in kyphosis or lordosis. A sagittal image of the spine was obtained to analyze the lumbosacral angle and to guide the imaging of transverse sections through each disc (L1/L2 to L5/S1). ⋯ The corresponding values for kyphosis were 49-57 mm (ES) and 67-77 mm (ESA), respectively. Thus, there was a considerable effect (10-24%) of lumbar curvature on lever arm lengths for the back extensor muscles. The change in leverage will affect the need for extensor muscle force and thus the magnitude of compression in the lumbar spine in loading situations such as lifting.