• Spine · Jun 2013

    Feasibility of laminar screw placement in the upper thoracic spine: analysis using 3-dimensional computed tomographic simulation.

    • Mary Ruth Alfonso Padua, Jin S Yeom, Huynh Thong Em, Ho-Joong Kim, Bong-Soon Chang, Choon-Ki Lee, and K Daniel Riew.
    • Spine Center and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, Sungnam, Korea.
    • Spine. 2013 Jun 1;38(13):1146-53.

    Study DesignEvaluation using 3-dimensional screw trajectory software and computed tomographic scans.ObjectiveTo investigate the anatomic feasibility of laminar screw placement in the upper thoracic spine compared with pedicle screw placement.Summary Of Background DataAlthough laminar screws have been suggested as an alternative to pedicle screws in the upper thoracic spine, previous anatomic feasibility studies have some limitations.MethodsFour types of screws were simulated from T1 to T6: unilaminar screw (US), superior bilaminar screw (SBS), inferior bilaminar screw (IBS), and pedicle screw (PS). Maximum allowable screw dimensions and the success rates of 4.5-mm screw placement were compared for each level. Laminar screw dimensions with more than 90% success rate at each level were determined for reference.ResultsComputed tomographic scans of 132 patients were analyzed. Laminar screw diameters gradually increased from T1 (4.4-5.4 mm, for each type) to T6 (4.8-6.7 mm), whereas PS diameter steeply declined from T1 (5.9 mm) to T4 (3.4 mm) and then leveled off. At T1, PS had greater success rate of 4.5-mm screw placement than laminar screws (US > IBS > SBS); at T2, US had greater success rate than IBS, followed by PS and SBS; and at T3 to T6, laminar screws (US > IBS > SBS) had greater success rate than PS in all comparisons. Except for SBS at T1, laminar screw diameters with more than 90% success rates were between 3.5 and 5.0 mm.ConclusionIn view of their anatomic feasibility, laminar screws can be a viable alternative to PSs in the upper thoracic spine. Particularly at T3 to T6 where the pedicle width is inherently small, the success rates of laminar screw placement were significantly and consistently higher than those of PS placement. The comparable success rates of laminar screws using commercially available screw sizes further emphasize their potential clinical use.

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