Biomechanical and Clinical Research, Alphatec Spine Inc., 5818 El Camino Real, Carlsbad, CA 92008, USA.
Spine J. 2011 Aug;11(8):777-81. doi: 10.1016/j.spinee.2011.06.006. Epub 2011 Jul 29.
Pedicle screws are now standard for spinal arthrodesis as they provide three-column spinal stabilization. Decreased vertebral body bone density because of aging reduces the stability of the bone-screw interface, potentially increasing screw pullout or pseudarthrosis. Modifications to standard pedicle screw designs to improve screw stabilization may help to compensate for the detrimental effects of decreased vertebral bone density.
To evaluate differences in initial pullout strength of an expandable titanium pedicle screw as compared with a standard titanium pedicle screw.
In vitro human cadaveric biomechanical investigation.
Fresh thoracolumbar spines from four human cadavers were imaged using quantitative computed tomography to obtain standard lumbar osteoporosis (Dual-energy X-ray absorptiometry [DXA]) T scores. Six bodies were sectioned per spine, and standard titanium 6.5-mm diameter pedicle screws and expandable 6.5-mm diameter titanium screws (maximum expanded diameter=10 mm) were randomized to right and left sides. Screw testing, in axial pullout at 25 mm/min, was randomized to reduce the effects of testing order. Data for stiffness (N/mm), yield load (N), ultimate load (N), and energy (N mm) (area under the load-displacement curve) were analyzed using a one-way analysis of variance (p<.05).
Lumbar DXA scores averaged -3.6. There were no statistical differences between screw types for stiffness. Yield load was not statistically different between groups, although the expandable screw yield load was nearly 25% greater than that of the standard screw. Ultimate load was found to be statistically greater (∼30%) for the expandable screw compared with the standard screw (p<.05). The energy required to cause bone-implant failure was also statistically greater for the expandable screw compared with the standard screw (p<.0001).
Expandable titanium pedicle screws demonstrated improved screw pullout stability compared with standard titanium screws in osteopenic or osteoporotic bone. Further studies are warranted examining other loading methods to evaluate the stability provided by an expandable pedicle screw.
如今，椎弓根螺钉已成为脊柱关节融合术的标准方法，因为它们提供了三柱脊柱稳定性。由于年龄增长导致椎体骨密度降低，会降低骨-螺钉界面的稳定性，从而增加螺钉拔出或假关节形成的风险。对标准椎弓根螺钉设计进行改进以增强螺钉稳定性，可能有助于补偿椎体骨密度降低的不利影响。
评估可扩张钛制椎弓根螺钉与标准钛制椎弓根螺钉初始拔出强度的差异。
体外人体尸体生物力学研究。
对 4 具人体尸体的胸腰椎进行定量计算机断层扫描，以获得标准腰椎骨质疏松症（双能 X 射线吸收法[DXA]）T 评分。每具脊柱均有 6 个节段被切开，将标准的 6.5mm 直径钛制椎弓根螺钉和可扩张的 6.5mm 直径钛制螺钉（最大扩张直径=10mm）随机分配到右侧和左侧。螺钉测试采用 25mm/min 的轴向拔出方式，随机化以减少测试顺序的影响。使用单因素方差分析（p<.05）对刚度（N/mm）、屈服载荷（N）、极限载荷（N）和能量（N·mm）（载荷-位移曲线下的面积）进行数据分析。
腰椎 DXA 评分为-3.6。在刚度方面，两种螺钉类型之间无统计学差异。虽然可扩张螺钉的屈服载荷比标准螺钉高近 25%，但组间差异无统计学意义。与标准螺钉相比，可扩张螺钉的极限载荷显著增加（约 30%）（p<.05）。与标准螺钉相比，可扩张螺钉引起骨-植入物失效所需的能量也显著增加（p<.0001）。
与标准钛制螺钉相比，在骨质疏松或骨质疏松性骨中，可扩张钛制椎弓根螺钉显示出更好的螺钉拔出稳定性。进一步的研究需要检查其他加载方法，以评估可扩张椎弓根螺钉提供的稳定性。
