Spinal Biomechanics Laboratory, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA.
Neurosurgery. 2010 Mar;66(3 Suppl Operative):126-32; discussion 132-3. doi: 10.1227/01.NEU.0000348561.59062.A2.
To study the alteration to normal biomechanics after insertion of a lumbar interspinous spacer (ISS) in vitro by nondestructive cadaveric flexibility testing.
Seven human cadaveric specimens were studied before and after ISS placement at L1-L2. Angular range of motion, lax zone, stiff zone, sagittal instantaneous axis of rotation (IAR), foraminal height, and facet loads were compared between conditions. Flexion, extension, lateral bending, and axial rotation were induced using pure moments (7.5 Nm maximum) while recording motion optoelectronically. The IAR was measured during loading with a 400 N compressive follower. Foraminal height changes were calculated using rigid body methods. Facet loads were assessed from surface strain and neural network analysis.
After ISS insertion, range of motion and stiff zone during extension were significantly reduced (P < .01). Foraminal height was significantly reduced from flexion to extension in both normal and ISS-implanted conditions; there was significantly less reduction in foraminal height during extension with the ISS in place. The ISS reduced the mean facet load by 30% during flexion (P < .02) and 69% during extension (P < .015). The IAR after ISS implantation was less than 1 mm from the normal position (P > .18).
The primary biomechanical effect of the ISS was reduced extension with associated reduced facet loads and smaller decrease in foraminal height. The ISS had little effect on sagittal IAR or on motion or facet loads in other directions.
通过非破坏性尸体柔韧性测试，体外研究腰椎棘突间 spacer（ISS）置入后对正常生物力学的改变。
7 个人体尸体标本在 L1-L2 置入 ISS 前后进行研究。在条件之间比较了运动范围、松弛区、僵硬区、矢状面瞬时旋转轴（IAR）、椎间孔高度和小关节负荷。使用纯力矩（最大 7.5 Nm）在诱导屈伸、侧屈和轴向旋转时，通过光电记录运动。在施加 400 N 压缩随动器时测量 IAR。使用刚体方法计算椎间孔高度变化。通过表面应变和神经网络分析评估小关节负荷。
ISS 插入后，伸展时的运动范围和僵硬区明显减少（P <.01）。在正常和 ISS 植入条件下，椎间孔高度从屈伸到伸展都显著降低；ISS 在位时，伸展时椎间孔高度的降低明显减少。ISS 在屈曲时将平均小关节负荷降低了 30%（P <.02），在伸展时降低了 69%（P <.015）。ISS 植入后 IAR 距正常位置不到 1 毫米（P >.18）。
ISS 的主要生物力学效应是减少伸展运动，同时伴有小关节负荷降低和椎间孔高度降低减少。ISS 对矢状面 IAR 或其他方向的运动或小关节负荷几乎没有影响。
