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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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.
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Intraoperative spinal ultrasonography (IOSS) was used to evaluate and monitor the spinal cord in 49 patients with cervical myelopathy. Intraoperative spinal ultrasonography demonstrated movements of the dura mater and the spinal cord at the cardiac rate, with some variability in intensity and mode. It also delineated the anterior surface of the spinal canal and configuration of the spinal cord. ⋯ Spinal cord motions were surmised to be generated not only by the anterior spinal artery, but also by other factors. Dural pulsations clearly did not always imply the absence of compression of the spinal cord. Intraoperative spinal ultrasonography was thus quite useful for monitoring decompression in cervical myelopathy.