Spine
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Pedicle screw fixation alone for sequential spinal instabilities was biomechanically compared with pedicle screw fixation using interbody cages. ⋯ For spinal instability with preserved anterior load sharing, pedicle screw fixation alone is biomechanically adequate, and interbody cages should not be used because they further increase segmental motion at the adjacent segment. However, PS alone provides insufficient stability and high implant strain in case of damaged anterior column. In such cases, additional interbody cages significantly increase construct stiffness and decrease hardware strain. However, they increase ROM at the adjacent segment as well.
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A biomechanical cadaveric study of thoracic and lumbar vertebrae with simulated metastases quantifying intravertebral pressures during transpedicular vertebroplasty. ⋯ Percutaneous vertebroplasty produces higher intravertebral pressures in vertebrae containing a simulated lytic metastasis than in intact vertebrae. Pressures generated in the tumor specimens are sufficiently elevated to cause embolic phenomena.
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Various amounts of static mechanical load were applied to mouse intervertebral discs in organ cultures. The apoptosis then was examined using nick end labeling. Two mitogen-activated protein kinase (MAPK) inhibitors were added to the medium. ⋯ Chondrocyte apoptosis was induced using a static mechanical load especially in the cartilaginous endplate in an organ culture. Apoptosis occurred similarly to previous findings using an in vivo model. This culture system thus reflected the apoptosis demonstrated in vivo. Because biologically active reagents such as MAPK inhibitors can be simply added to culture media, this system may be a useful method for detecting factors that influence apoptosis induced by mechanical stress. Both MAPK inhibitors increased the occurrence of apoptosis. This suggests that these two MAPKs can counteract the apoptotic pathway induced by mechanical stress.
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An in vitro biomechanical study of adjacent segment motion (at L3-L4 and L5-S1) after a simulated lumbar interbody fusion of L4-L5 in different sagittal alignments was carried out. ⋯ Hypolordotic alignment at L4-L5 caused the greatest amount of flexion-extension motion at L3-L4, and the differences were statistically significant in comparison with intact specimen, in situ fixation, and hyperlordotic fixation. Hyperlordotic alignment at L4-L5 caused the greatest amount of flexion-extension motion at L5-S1, and the difference was statistically significant in comparison with intact specimen but not in situ fixation or hypolordotic fixation.
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A rare case of Baastrup's disease as a cause of spinal canal stenosis in a patient with double-level spondylolisthesis is reported. ⋯ Baastrup's disease leading to neoarthrosis formation with synovial cavity and causing low back pain has been reported previously. The cyst can enter into the epidural space through the midline cleft of the ligamentum flavum to result in extradural compression.