Department of Neurosurgery, Baylor College of Medicine, Houston, Texas 77030-2505, USA.
Neurosurgery. 2011 Sep;69(3):733-44. doi: 10.1227/NEU.0b013e31821cc499.
There is an increased incidence of fractures in untreated adjacent vertebrae after vertebroplasty.
To introduce unconstrained 6 degrees of freedom biomechanical testing to investigate whether vertebroplasty lowered the fracture strength of adjacent untreated vertebrae under physiological loading conditions and to describe the observed fracture pattern.
Three-level spinal segments (T10-12 and L1-3) from 6 spines were tested under unconstrained axial compression in which shear forces and torque were minimized using a 6-degrees of freedom robotic arm. Fracture initiation loads and ultimate failure loads of lumbar segments were predicted from the corresponding thoracic segments by assuming constant fracture stress along the spinal column. The predicted values were compared with postvertebroplasty experimental values of the lumbar spine segments. Plain radiographs were taken at 600-N increments to record the developing fracture pattern.
All 6 vertebroplasty group specimens experienced reductions in fracture strengths ranging from 27.4% to 47.6% with an average decrease of 32.6% (P < .002) and reductions in ultimate failure load ranging from 1.6% to 47.3%, with an average decrease of 34.7% (P < .003) compared with predicted values from the nonvertebroplasty group. In all vertebroplasty group specimens, the superior and inferior endplates of the untreated middle vertebral body (L2) were deflected, whereas 5 of the 6 nonvertebroplasty group specimens did not show any evidence of endplate deflection.
Vertebroplasty altered the load transfer along the anterior spinal column, thereby statistically significantly increasing fracture risk and ultimate failure load of the untreated adjacent vertebrae. The radiographic findings support the endplate deflection fracture mechanism as the cause of adjacent fractures after vertebroplasty.
椎体成形术后未治疗的相邻椎体骨折发生率增加。
引入无约束的 6 自由度生物力学测试，以研究椎体成形术是否会降低生理负荷条件下未治疗的相邻椎体的骨折强度，并描述观察到的骨折模式。
使用 6 自由度机器人臂最小化剪切力和扭矩，对来自 6 个脊柱的 3 个节段（T10-12 和 L1-3）进行无约束轴向压缩测试。通过假设脊柱段的骨折应力恒定，从相应的胸椎段预测腰椎段的骨折起始载荷和最终破坏载荷。将预测值与腰椎节段椎体成形术后的实验值进行比较。在 600-N 增量时拍摄平片，以记录发展中的骨折模式。
所有 6 个椎体成形术组标本的骨折强度均降低，范围为 27.4%至 47.6%，平均降低 32.6%（P<0.002），最终破坏载荷降低 1.6%至 47.3%，平均降低 34.7%（P<0.003）与非椎体成形术组的预测值相比。在所有椎体成形术组标本中，未治疗的中间椎体（L2）的上下终板均发生了偏转，而 6 个非椎体成形术组标本中有 5 个没有出现终板偏转的证据。
椎体成形术改变了前脊柱段的载荷传递，从而显著增加了未治疗的相邻椎体的骨折风险和最终破坏载荷。影像学发现支持终板偏转骨折机制是椎体成形术后相邻骨折的原因。
