The spine journal : official journal of the North American Spine Society
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Surgical instrumentation used for posterior craniocervical instability has evolved from simple wiring techniques to sophisticated implant systems that incorporate multiple means of rigid fixation for the cervical spine. Polyaxial screws and lamina hooks in conjunction with occipital plating and transitional rods for caudal fixation theoretically allow for fixation points at each vertebra along the posterior aspect of the cervical spine. However, the potential for anatomical constraints to prevent intraoperative instrumentation at the desired vertebral level exists. The biomechanical implications of such "skipped segments" have not been well documented. ⋯ There was no statistical difference between the three-point fixation treatment group and the sequential fixation group in flexion extension bending. Lateral bending and axial rotation demonstrated an increase in total overall ROM with partial fixation compared with fixation at all levels. Axial rotation in particular showed increased mobility in the lower cervical spine for the partial fixation group. In the instance where surgeons are not able to apply sequential fixation at diseased levels, especially for the lower subaxial cervical spine, particular attention to limitation of lateral bending and axial rotation by the use of external orthotics must be considered.
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Two common justifications for orienting cervical screws in an angled direction are to increase pullout strength and to allow use of longer screws. This concept is widely taught and has guided implant design. Fixed- versus variable-angle systems may offer strength advantages. Despite these teachings, there is a paucity of supporting biomechanical evidence. The purpose of our study is to test the influence of screw orientation and plate design on the maximum screw pullout force. ⋯ In this system, a variable-angle plate has greater pullout strength than a fixed-angle plate, regardless of the orientation of screws. With the variable-angle plate, a construct of all screws 12 degrees "up and in" is the weakest configuration. We found that with the 90 degrees construct, both 16- and 14-mm screws performed significantly better than 16-mm convergent screws. These findings are remarkable because they contradict the current doctrine. This may be a function of plate-dependent factors and should not be applied universally to all plate systems. Further study of screw orientation in additional plating systems is warranted.
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Lumbar intervertebral disc degeneration (DD) precedes degenerative diseases of the lumbar spine. Various factors in addition to normal aging are reported to be associated with DD, and recently atherosclerosis and risk factors for cardiovascular diseases (cardiovascular risk factors) have received much attention; however, the links between these risk factors and DD are unclear. ⋯ Aging, high BMI, high LDLc, occupational lifting, and sports activities are associated with DD. The results of this study raise our index of suspicion that cardiovascular risk factors and particular physical loading may contribute to DD; however additional studies are required to further investigate associations between DD and these factors.
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A growing population of patients with osteoporosis and fragility fractures has developed. Fragility fractures, including vertebral compression fractures, have been associated with increased mortality. Early operative interventions for patients sustaining hip fractures have been found to reduce mortality. ⋯ Kyphoplasty did not seem to effect the survival of patients with a vertebral compression fracture.