Charles Y P, Pelletier H, Hydier P, Schuller S, Garnon J, Sauleau E A, Steib J-P, Clavert P
Groupe d'étude de biomécanique ostéo-articulaire de Strasbourg (GEBOAS), fédération de médecine translationnelle de Strasbourg (FMTS), université de Strasbourg, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Service de chirurgie du rachis, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP 426, 67091 Strasbourg cedex, France.
Institut national des sciences appliquées (INSA), université de Strasbourg, 24, boulevard de la Victoire, 67000 Strasbourg, France; Institut Charles-Sadron, UPR 22 CNRS, université de Strasbourg, 23, rue du Loess, 67000 Strasbourg, France.
Orthop Traumatol Surg Res. 2015 May;101(3):369-74. doi: 10.1016/j.otsr.2015.01.005. Epub 2015 Mar 6.
Vertebroplasty prefilling or fenestrated pedicle screw augmentation can be used to enhance pullout resistance in elderly patients. It is not clear which method offers the most reliable fixation strength if axial pullout and a bending moment is applied. The purpose of this study is to validate a new in vitro model aimed to reproduce a cut out mechanism of lumbar pedicle screws, to compare fixation strength in elderly spines with different cement augmentation techniques and to analyze factors that might influence the failure pattern.
Six human specimens (82-100 years) were instrumented percutaneously at L2, L3 and L4 by non-augmented screws, vertebroplasty augmentation and fenestrated screws. Cement distribution (2 ml PMMA) was analyzed on CT. Vertebral endplates and the rod were oriented at 45° to the horizontal plane. The vertebral body was held by resin in a cylinder, linked to an unconstrained pivot, on which traction (10 N/s) was applied until rupture. Load-displacement curves were compared to simultaneous video recordings.
Median pullout forces were 488.5 N (195-500) for non-augmented screws, 643.5 N (270-1050) for vertebroplasty augmentation and 943.5 N (750-1084) for fenestrated screws. Cement augmentation through fenestrated screws led to significantly higher rupture forces compared to non-augmented screws (P=0.0039). The pullout force after vertebroplasty was variable and linked to cement distribution. A cement bolus around the distal screw tip led to pullout forces similar to non-augmented screws. A proximal cement bolus, as it was observed in fenestrated screws, led to higher pullout resistance. This cement distribution led to vertebral body fractures prior to screw pullout.
The experimental setup tended to reproduce a pullout mechanism observed on radiographs, combining axial pullout and a bending moment. Cement augmentation with fenestrated screws increased pullout resistance significantly, whereas the fixation strength with the vertebroplasty prefilling method was linked to the cement distribution.
椎体成形术预填充或开窗椎弓根螺钉强化可用于增强老年患者的拔出阻力。如果施加轴向拔出力和弯矩，尚不清楚哪种方法能提供最可靠的固定强度。本研究的目的是验证一种新的体外模型，该模型旨在重现腰椎椎弓根螺钉的拔出机制，比较不同骨水泥强化技术在老年脊柱中的固定强度，并分析可能影响失效模式的因素。
对6例82 - 100岁的人体标本，在L2、L3和L4节段经皮植入非强化螺钉、椎体成形术强化螺钉和开窗螺钉。通过CT分析骨水泥分布情况（2 ml聚甲基丙烯酸甲酯）。椎体终板和连接杆与水平面呈45°角。椎体用树脂固定在一个圆柱体中，连接到一个无约束的枢轴上，在枢轴上施加牵引力（10 N/s）直至断裂。将载荷 - 位移曲线与同步视频记录进行比较。
非强化螺钉的中位拔出力为488.5 N（195 - 500），椎体成形术强化螺钉为643.5 N（270 - 1050），开窗螺钉为943.5 N（750 - 1084）。与非强化螺钉相比，开窗螺钉进行骨水泥强化导致的断裂力显著更高（P = 0.0039）。椎体成形术后的拔出力存在差异，且与骨水泥分布有关。螺钉尖端远端周围的骨水泥团块导致的拔出力与非强化螺钉相似。如在开窗螺钉中观察到的近端骨水泥团块，则导致更高的拔出阻力。这种骨水泥分布导致在螺钉拔出之前椎体骨折。
该实验装置倾向于重现X线片上观察到的拔出机制，结合了轴向拔出力和弯矩。开窗螺钉进行骨水泥强化显著增加了拔出阻力，而椎体成形术预填充方法的固定强度与骨水泥分布有关。
