Integrated Department of Orthopaedic Surgery and Rehabilitation, Walter Reed National Military Medical Center, Washington, DC, USA.
Spine (Phila Pa 1976). 2012 Sep 1;37(19):E1171-6. doi: 10.1097/BRS.0b013e31825eb8fb.
A human cadaveric biomechanical analysis.
The purpose of this study was to evaluate the bone density/trabecular width of the thoracic pedicle and correlate that with its resistance against compressive loading used during correction maneuvers in the thoracic spine (i.e., cantilever bending).
As surgeons perform cantilever correction maneuvers in the spine, it is common to have pedicle screws pullout or displace while placing corrective forces on the construct. Currently, surgeons either compress against the cephalad aspect of the pedicle or vice versa. We set out to establish which aspect of the pedicle was the most dense and to determine the optimal direction for screw compression during kyphosis/deformity correction.
Fifteen fresh-frozen cadaveric vertebrae (n = 15) were examined by micro-computed tomography to determine percent bone volume/total volume (%BV/TV) within the cephalad and caudad aspects of the pedicle. Specimens were sectioned in the sagittal plane. Pedicles were instrumented according to the straightforward trajectory on both sides. Specimens were then mounted and loading to failure was performed perpendicular to the screw axis (either the cephalad or the caudad aspect of the pedicle).
Mean failure when loading against the caudad aspect of the pedicle was statistically, significantly greater (454.5 ± 241.3 N vs. 334.79 1 ± 158.435 N) than for the cephalad pedicle (P < 0.001). In concordance with failure data, more trabecular and cortical bones were observed within the caudad half of the pedicle compared with the cephalad half (P < 0.001).
Our results suggest that the caudad half of the pedicle is denser and withstands higher forces compared with the cephalad aspect. In turn, the incidence of intraoperative screw loosening and/or pedicle fracture may be reduced if the compressive forces (cantilever bending during deformity correction) placed upon the construct are applied against the caudad portion of the pedicle.
人体尸体生物力学分析。
本研究的目的是评估胸椎椎弓根的骨密度/小梁宽度，并将其与在胸椎（即悬臂弯曲）校正操作过程中抵抗压缩载荷的能力相关联。
当外科医生在脊柱上进行悬臂校正操作时，椎弓根螺钉拔出或移位是很常见的，同时对构建物施加矫正力。目前，外科医生要么压在椎弓根的头侧，要么反之。我们的目的是确定椎弓根最密集的部位，并确定在脊柱后凸/畸形矫正过程中螺钉压缩的最佳方向。
通过微计算机断层扫描检查 15 个新鲜冷冻尸体椎体（n = 15），以确定椎弓根头侧和尾侧的骨体积/总体积百分比（%BV/TV）。标本在矢状面切开。根据简单的轨迹在两侧对椎弓根进行器械操作。然后将标本安装，并沿螺钉轴垂直（椎弓根的头侧或尾侧）进行失效加载。
当加载到椎弓根尾侧时，平均失效明显更高（454.5 ± 241.3 N 比 334.79 1 ± 158.435 N）（P < 0.001）。与失效数据一致，与椎弓根头侧相比，在椎弓根尾侧观察到更多的小梁骨和皮质骨（P < 0.001）。
我们的结果表明，与头侧相比，椎弓根尾侧更密集，能够承受更高的力。因此，如果在构建物上施加的压缩力（在畸形校正期间的悬臂弯曲）施加在椎弓根的尾侧部分，术中螺钉松动和/或椎弓根骨折的发生率可能会降低。
