椎体成形术对胸腰椎爆裂型骨折的治疗意义

目的：探讨腰腰椎爆裂型骨折撑开复位与椎体成形术后椎体结构和生物力学性能的变化。方法：收集6具新鲜成人尸体的胸腰椎标本，制成T11－L1、L2－L4、T12－L2节段标本共10具，用自由落体撞击试验造成中间椎体爆裂型骨折，撑开复位、用注射型自固定磷酸钙人工骨行椎体成形术。分别于骨折前、骨折撑开复位后、椎体成形术后用薄层CT扫描测量中间椎体内空隙，用双能X线骨密度仪测定骨密度，用万能材料试验机测定骨折前、椎体成形术后中间椎体与其上方椎间盘在前屈、后伸、侧屈和扭转就压力 下刚度的变化，并比较成形术后的伤椎及其下方的完整椎体的抗极限压缩测试结果。结果：8具标本造中间椎体爆裂型骨折模型成功。（1）骨折前椎体内无明显空隙；骨折并撑开复位后椎体内空隙体积平均为5．25cm^3，占椎体总体积的13．9％；椎体成形术后空隙减少，与骨折前相比差异无显著性意义。（2）骨折前椎体骨密度在正常范围，骨折并撑开复位后骨密度较骨折前降低；椎体成形术后，骨密度较骨折复位后及骨折前均明显升高。（3）椎体成形术后，伤椎的刚度与骨折前相比差异无显著性意义，抗极限压缩强度的均值低于其下方完整椎体，但差异无显著性意义；伤椎上方椎间盘在前屈和后伸应力下的刚度小于骨折前，但在侧屈应力下差异无显著性意义；标本在扭转应力下的刚度小于骨折前。结论：（1）撑开复位未能恢复胸腰椎爆裂型骨折椎体结构上的完整性，这可能是后路切开复位内固定术后发生内固定失败与矫正度丢失的重要原因。（2）应用注射型自固化磷酸钙人工骨行椎体成形术有助于伤椎的重建，术后脊柱的生物力学特性接近骨折前水平。

Vertebroplasty for treatment of thoracolumbar burst fractures

Objective Short-segment pedicle instrumentation for thoracolumbar burst fracture was known to have a relatively high incidence of failure and correction loss, intracorporeal gap secondary to reduction being probable causes. The purpose of this study was to evaluate the intracorporeal gap after reduction and the biomechanical effect of vertebroplasty on thoracolumbar burst fractures. Methods Six fresh adult thoracolumbar specimens were collected, and 10 segmental specimens (T11-L1, L2-L4, T12-L2) were processed. Burst fracture was created using free-drop test. Then the fractures were reduced and augmented with injectable self-setting calcium phosphate cement. The intracorporeal gap and bone mineral density(BMD) were measured using spiral CT and dual energy X-ray absorptiometry(DEXA) before fracture, after reduction and after vertebroplasty respectively. The stiffness in middle vertebrae and above discs were measured under flexion, extension, lateral flexion and torsion stress before fracture and after augmentation. The ultimate strength against compression was tested in the augmented vertebrae and the integral vertebrae below it. Results Burst fractures were created in eight of ten specimens. 1) There was no evident intracorporeal gap before fracture, which appeared after reduction with average volume of 5.25 cm3 (13.9% of total corporal volume), and it decreased to normal level after vertebroplasty. 2) The BMD was normal in all specimens before fracture, which decreased significantly after fracture reduction, and it was significantly higher after vertebroplasty than that before fracture or after reduction. 3) There was no significant difference of stiffness in vertebrae before fractures and after augmentation. The mean value of ultimate strength against compression in the augmented vertebrae decreased slightly but not significantly in contrast to the vertebrae below it. In contrast to the value before fracture, the stiffness of above discs decreased significantly under flexion and extension stress but not significantly under lateral flexion stress after augmentation, while the stiffness of the specimen decreased significantly under torsion stress. Conclusion 1) Posterior reduction in thoracolumbar burst fracture can not reestablish intact corporeal structure, which may be an important cause of postoperative implant failure and correction loss. 2) Vertebroplasty with injectable self-setting calcium phosphate cement is helpful to reestablish intact corporeal structure, and restore stiffness and strength of the injured corpora nearly to its initial value.