Colman Matthew, Pond Jonathan, Bachus Kent, Lawrence Brandon D, Spiker William R, Brodke Darrel S
*Departments of Orthopaedic Surgery, University of Utah, Salt Lake City, UT †Aurora Sheboygan Medical Center, Sheboygan, WI.
Clin Spine Surg. 2017 Apr;30(3):E252-E256. doi: 10.1097/BSD.0000000000000228.
Biomechanics.
The objective of this study was to compare the fixation in osteoporotic specimens of a bicortical sacral pedicle screw to the following constructs: a unicortical solid screw augmented with polymethylmethacrylate (PMMA) (TRACT), a unicortical fenestrated screw augmented with PMMA (FEN), and a bicortical screw/sacral alar screw combination (PED/ALA).
Rigid posterior sacral fixation of osteoporotic spines is problematic due to poor bone quality. Options to improve fixation include bicortical or tricortical screw trajectory, addition of S2 alar screws, or PMMA augmentation.
Eleven osteoporotic cadaveric sacra were potted in 2-part filler compound. As a baseline fixation method, a 6.5-mm bicortical pedicle screw was placed into 1 pedicle of each sacra. The contralateral side was randomly assigned to receive a unicortical fenestrated 6.5-mm pedicle screw augmented with PMMA, a unicortical solid 6.5-mm pedicle screw augmented with PMMA, or a bicortical pedicle screw/alar screw construct. Pedicle screws were failed in cantilever pullout using a materials testing machine. Data were normalized into a test index by taking the ratio of the test screw pullout strength to the intraspecimen bicortical control screw pullout strength.
The fixation strengths as expressed by the test index of the TRACT, FEN, and PED/ALA groups were 101%, 157%, and 167%, respectively. Although there was no statistical difference detected between the FEN and PED/ALA groups, the TRACT group had a trend toward lower pullout strength than the FEN (P=0.06) or PED/ALA (0.06) groups. Although underpowered, this study did not detect biomechanical inferiority for any of the 3 test configurations when compared with standard bicortical S1 screws.
The data indicate that the fixation strength of a fenestrated, PMMA-augmented construct or a combined S1 pedicle/S2 alar screw construct may be better than either standard bicortical or unicortical PMMA screw-tract augmented screws.
生物力学。
本研究的目的是比较双皮质骶椎椎弓根螺钉在骨质疏松标本中的固定效果与以下几种固定结构：用聚甲基丙烯酸甲酯（PMMA）增强的单皮质实心螺钉（TRACT）、用PMMA增强的单皮质开窗螺钉（FEN）以及双皮质螺钉/骶骨翼螺钉组合（PED/ALA）。
由于骨质质量差，骨质疏松性脊柱的坚强后路骶骨固定存在问题。改善固定的方法包括双皮质或三皮质螺钉轨迹、增加S2翼螺钉或PMMA增强。
将11个骨质疏松的尸体骶骨用双组分填充化合物灌封。作为基线固定方法，在每个骶骨的1个椎弓根中置入1枚6.5毫米双皮质椎弓根螺钉。对侧随机分配接受用PMMA增强的单皮质开窗6.5毫米椎弓根螺钉、用PMMA增强的单皮质实心6.5毫米椎弓根螺钉或双皮质椎弓根螺钉/翼螺钉结构。使用材料试验机对椎弓根螺钉进行悬臂拔出试验。通过将试验螺钉拔出强度与标本内双皮质对照螺钉拔出强度的比值，将数据标准化为试验指数。
TRACT组、FEN组和PED/ALA组的试验指数所表示的固定强度分别为101%、157%和167%。虽然FEN组和PED/ALA组之间未检测到统计学差异，但TRACT组的拔出强度有低于FEN组（P = 0.06）或PED/ALA组（0.06）的趋势。尽管效能不足，但与标准双皮质S1螺钉相比，本研究未检测到这3种试验构型中的任何一种在生物力学上的劣势。
数据表明，开窗、PMMA增强的固定结构或联合S1椎弓根/S2翼螺钉结构的固定强度可能优于标准双皮质或单皮质PMMA螺钉轨迹增强螺钉。
