Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Chang Gung University, Taoyuan, Taiwan.
BMC Musculoskelet Disord. 2011 Feb 1;12:33. doi: 10.1186/1471-2474-12-33.
Pedicle screws with PMMA cement augmentation have been shown to significantly improve the fixation strength in a severely osteoporotic spine. However, the efficacy of screw fixation for different cement augmentation techniques, namely solid screws with retrograde cement pre-filling versus cannulated screws with cement injection through perforation, remains unknown. This study aimed to determine the difference in pullout strength between conical and cylindrical screws based on the aforementioned cement augmentation techniques. The potential loss of fixation upon partial screw removal after screw insertion was also examined.
The Taguchi method with an L8 array was employed to determine the significance of design factors. Conical and cylindrical pedicle screws with solid or cannulated designs were installed using two different screw augmentation techniques: solid screws with retrograde cement pre-filling and cannulated screws with cement injection through perforation. Uniform synthetic bones (test block) simulating severe osteoporosis were used to provide a platform for each screw design and cement augmentation technique. Pedicle screws at full insertion and after a 360-degree back-out from full insertion were then tested for axial pullout failure using a mechanical testing machine.
The results revealed the following 1) Regardless of the screw outer geometry (conical or cylindrical), solid screws with retrograde cement pre-filling exhibited significantly higher pullout strength than did cannulated screws with cement injection through perforation (p = 0.0129 for conical screws; p = 0.005 for cylindrical screws). 2) For a given cement augmentation technique (screws without cement augmentation, cannulated screws with cement injection or solid screws with cement pre-filling), no significant difference in pullout strength was found between conical and cylindrical screws (p >0.05). 3) Cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Observations of the failed specimens indicated that failure occurred at the composite/bone interface, whereas the composite remained well bonded to the screws. This result implies that the screw/composite interfacial strength was much higher than the composite/bone interfacial strength. 4) The back-out of the screw by 360 degrees from full insertion did not decrease the pullout strength in any of the studied cases. 5) Generally, larger standard deviations were found for the screw back-out cases, implying that the results of full insertion cases are more repeatable than those of the back-out cases.
Solid screws with retrograde cement pre-filling offer improved initial fixation strength when compared to that of cannulated screws with cement injection through perforation for both the conically and cylindrically shaped screw. Our results also suggest that the fixation screws can be backed out by 360 degrees for intra-operative adjustment without the loss of fixation strength.
带 PMMA 水泥增强剂的椎弓根螺钉已被证明可显著提高严重骨质疏松脊柱的固定强度。然而，不同的水泥增强技术的螺钉固定效果，即逆行预填实心螺钉与通过穿孔注射水泥的空心螺钉，仍不清楚。本研究旨在确定基于上述水泥增强技术的锥形和圆柱形螺钉之间的拔出强度差异。还检查了螺钉插入后部分螺钉移除时固定的潜在损失。
采用 L8 阵列的 Taguchi 法确定设计因素的重要性。使用两种不同的螺钉增强技术安装锥形和圆柱形椎弓根螺钉：实心螺钉逆行预填水泥和空心螺钉通过穿孔注射水泥。均匀的合成骨（测试块）模拟严重骨质疏松症，为每个螺钉设计和水泥增强技术提供平台。使用机械试验机对完全插入的和从完全插入后退出 360 度的椎弓根螺钉进行轴向拔出失效测试。
结果表明：1）无论螺钉外几何形状（锥形或圆柱形）如何，逆行预填水泥的实心螺钉的拔出强度均明显高于通过穿孔注射水泥的空心螺钉（锥形螺钉 p=0.0129；圆柱形螺钉 p=0.005）。2）对于给定的水泥增强技术（无水泥增强、空心螺钉注射水泥或实心螺钉预填水泥），锥形和圆柱形螺钉之间的拔出强度无显著差异（p>0.05）。3）水泥渗透到测试块的开细胞中形成水泥/骨复合材料结构。对失效样本的观察表明，失效发生在复合材料/骨界面处，而复合材料仍与螺钉紧密结合。这一结果表明，螺钉/复合材料界面强度远高于复合材料/骨界面强度。4）从完全插入后退出螺钉 360 度不会降低任何研究案例中的拔出强度。5）一般来说，退出案例的标准偏差较大，这意味着完全插入案例的结果比退出案例的结果更具可重复性。
与通过穿孔注射水泥的空心螺钉相比，逆行预填水泥的实心螺钉可提高初始固定强度，无论是锥形还是圆柱形螺钉。我们的结果还表明，固定螺钉可以在不损失固定强度的情况下退出 360 度以进行术中调整。
