Journal of neurosurgery. Spine
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Radiographic and clinical evaluation of free-hand placement of C-2 pedicle screws. Clinical article.
Stabilization of the cervical spine can be challenging when instrumentation involves the axis. Fixation with C1-2 transarticular screws combined with posterior wiring and bone graft placement has yielded excellent fusion rates, but the technique is technically demanding and places the vertebral arteries (VAs) at risk. Placement of screws in the pars interarticularis of C-2 as described by Harms and Melcher has allowed rigid fixation with greater ease and theoretically decreases the risk to the VA. However, fluoroscopy is suggested to avoid penetration laterally, medially, and superiorly to avoid damage to the VA, spinal cord, and C1-2 joint, respectively. The authors describe how, after meticulous dissection of the C-2 pars interarticularis, such screws can be placed accurately and safely without the use of fluoroscopy. ⋯ Free-hand placement of screws in the C-2 pedicle can be done safely and effectively without the use of intraoperative fluoroscopy or navigation when the pars interarticularis/pedicle is assessed preoperatively with CT or MR imaging and found to be suitable for screw placement. When breaches do occur, they are overwhelmingly lateral in location, breach < 50% of the screw diameter, and in the authors' experience, are not clinically significant.
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Transpedicular instrumentation at C-7 has been well accepted, but salvage techniques are limited. Lamina screws have been shown to be a biomechanically sound salvage technique in the proximal thoracic spine, but have not been evaluated in the lower cervical spine. The following study evaluates the anatomical feasibility of lamina screws at C-7 as well as their bone-screw interface strength as a salvage technique. ⋯ These results suggest that using lamina screws as a salvage technique at C-7 provides similar fixation strength as the index pedicle screw. The C-7 lamina appears to have an ideal anatomical width for the insertion of 3.5-mm screws commonly used for cervical fusions. Therefore, if the transpedicular screw fails, using intralaminar screws appear to be a biomechanically sound salvage technique.
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The aim of this retrospective study was to evaluate the clinical usefulness of assessing lumbar somatosensory evoked potentials (SSEPs) in central lumbar spinal stenosis (LSS). ⋯ Lumbar SSEPs are able to detect neurological deficit in the lumbar area effectively, and they can reflect part of the subjective severity of sensory disturbance (numbness) in LSS. Both lumbar SSEPs and VAS scores of leg numbness may be useful for clinical evaluation in patients with LSS.
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In generalized osteoporosis, instrumentation with cement-augmented pedicle screws is an amplification of the therapeutic spectrum. Early clinical results are promising for both solid and cannulated screws; however, there are concerns regarding the revision characteristics of these screws, especially for the cannulated-fenestrated type with its continuous cement interconnection from the core of the screw to surrounding bone tissue. In a human cadaver model, bone mineral density (BMD) was assessed radiographically. ⋯ Thus, the revision characteristics of cement-augmented, cannulated-fenestrated pedicle screws are not problematic, even in cases of severe osteoporosis. The winglike cement interconnection between the screw core and surrounding bone tissue is fragile enough to break off in the event of an extraction torque and to release the screw. There is no proof to support the theoretical fear that while trying to remove a screw, the composite of screw and cement would not break but instead would rotate as a whole in the osteoporotic vertebral body.
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The authors' experience with treatment of 8 patients with "vertical mobile and reducible" atlantoaxial dislocation is reviewed. The probable pathogenesis, radiological and clinical features, and management issues in such cases are discussed. ⋯ Vertical mobile and reducible atlantoaxial dislocation is a discrete clinical entity. Abnormal inclination and incompetence of the facet joint appears to be the primary causative factor that resulted in vertical dislocation or basilar invagination. Posterior fixation in the reduced dislocation position forms the basis of treatment.