The spine journal : official journal of the North American Spine Society
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Comparative Study
Biomechanical comparison of two-level cervical locking posterior screw/rod and hook/rod techniques.
Locking posterior instrumentation in the cervical spine can be attached using 1) pedicle screws, 2) lateral mass screws, or 3) laminar hooks. This order of options is in order of decreasing technical difficulty and decreasing depth of fixation, and is thought to be in order of decreasing stability. ⋯ Individual pedicle screws are known to outperform lateral mass screws in terms of pullout resistance, but they offered no apparent advantage in terms of construct stability or failure of whole constructs. Larger standard deviations in anterior fixation imply more variability in the quality of fixation. In most loading modes, laminar hooks provided similar stability to lateral mass screws or pedicle screws; caudal laminar hooks are therefore an acceptable alternative posteriorly. Posterior two-level fixation is less variable and slightly more stable than anterior fixation. Combined instrumentation is significantly more stable than either anterior or posterior alone.
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Reconstruction of C2 after tumor destruction and resection remains a significant challenge. Most constructs use a strut graft with plate or screw fixation. A novel C2 prosthesis (cage/plate construct) combining a titanium mesh cage with bilateral C1 shelves and a T-plate has been used successfully in 18 patients. Supplemental posterior instrumentation includes C0-C3 or C1-C3 fixation. Biomechanical comparisons of this C2 prosthesis with traditional fixation options have not been reported. ⋯ Under acute loading conditions, both the cage/plate and strut graft/plate constructs provided initial stability beyond that of the intact specimen. For some reconstructions the occiput does not need to be included in the posterior instrumentation in order to obtain equivalent stability across the C1-C3 spinal space.
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Long-term results of patients treated with conventional laminoplasty have shown a significant number of patients complicated with kyphotic deformity. The authors hypothesize that by maintaining the spinous process-ligament-muscle complex (SPLMC) during laminoplasty, followed by postoperative muscle strengthening exercises, the formation of kyphosis can be decreased. ⋯ Laminoplasty with preservation of the SPLMC followed by appropriate postoperative muscle exercises may be an encouraging way to maintain or restore the physiological curve and prevent kyphotic deformity at a medium term follow-up.