单节段融合双节段置入物固定B型胸腰椎爆裂性骨折的生物力学研究

Biomechanical studies of single segmental spinal interbody fusion with bisegment fixation for thoracolumbar burst fracture type B

背景:胸腰椎爆裂骨折Dennis分型B型伤椎下位椎间盘无明显损伤,为了减少融合节段,保留正常间盘,单节段椎体融合(伤椎与上位椎体)手术方式已有人提出,但由于伤椎本身的损伤,切除部分椎体后置入固定螺钉容易松动,甚至无法固定。而将固定螺钉置入伤椎下位椎体,通过单节段融合双节段固定来稳定脊柱,是否完全可行尚无定论。目的:从生物力学角度观察单节段融合双节段置入物固定B型胸腰椎爆裂骨折的可行性。设计、时间及地点:随机分组设计,体外对比观察,于2007-06/2008-06在南方医科大学生物力学实验室完成。材料:取7～9月龄新鲜冰冻家猪胸腰椎标本(T13～L3节段)20具,其中10具为完整标本,10具为通过预损伤逐级撞击法制备的L1爆裂性骨折B型标本。方法:收集新鲜猪T13～L3节段胸腰椎标本,建立胸腰椎爆裂性骨折B型模型。实验分为4组,完整标本组(n=10):新鲜猪T13～L3节段标本;失稳组(n=10):采用预损伤逐级撞击法制备的L1爆裂性骨折B型标本;切除一椎间盘内固定组(n=10):失稳组经生物力学检测后,切除伤椎上位椎间盘连同椎体上1/2,取髂骨植骨,使用山东威高骨科材料有限公司U-FRONT胸腰椎前路双棒系统侧前方固定T14～L2椎体。切除两椎间盘内固定组(n=10):将切除一椎间盘内固定组检测后切除伤椎及下位椎间盘,髂骨植骨,用威高U-FRONT系统前侧方固定T14～L2椎体。植骨块长度比植骨区长1mm。主要观察指标:在三维运动试验机上检测并记录加载力矩为10N?m时各组T14～L2节段前屈、后伸、左右侧弯、轴向旋转的三维运动范围。结果:失穏组在伸屈、左右侧弯、轴向旋转方面表现出明显不稳,运动范围与完整标本组相比均明显增大(P<0.01)。切除一椎间盘内固定组及切除两椎间盘内固定组初始稳定性则有明显提高,伸屈、左右侧弯、轴向旋转运动范围与失稳组相比亦明显减小(P<0.05);两组标本伸屈、左右侧弯的运动范围与完整标本相比均明显减少,而轴向旋转运动范围明显增加(P<0.05)。切除一椎间盘内固定组轴向旋转小于切除两椎间盘内固定组(P<0.05)。结论:单节段融合双节段固定治疗胸腰椎爆裂骨折B型,在前屈、后伸、左右侧弯方向均有良好的初始稳定性,左右旋转初始稳定性较传统的切除两椎间盘伤椎次全切植骨内固定明显提高。

BACKGROUND： Thoracolumbar burst fracture Dennis type B does not have significant damage in the intervertebral discs of the inferior vertebral body. To reduce fusion segment and remain normal intercalated disc, single discectomy （damaged vertebral body and supervisor vertebral body） is proposed, but because of the damage to the vertebral body, implanted screw is easy to loose following excising partial vertebral body, even cannot be fixed. However, it is still unknown whether implanted screw in the inferior vertebral body of the damaged vertebral body was stabilized using two segment discectomy with fixation. OBJECTIVE： To analyze the feasibility of single segmental spinal interbody fusion with bisegment fixation for thoracolumbar burst fracture type B. DESIGN, TIME AND SETTING： The randomized controlled in vitro study was conducted at the Laboratory of Biomechanics, Southern Medical University from June 2007 to June 2008. MATERIALS： A total of 20 fresh freezing 7-9 months pig samples （T13-L3 segment） were used, comprising 10 integral samples and 10 L1 type B thoracolumbar burst fracture samples prepared by pre-injury and weight dropping technique. METHODS： Pig fresh thoracolumbar specimens from T13-L3 were collected to create models of type B thoracolumbar burst fracture. There were 4 groups in this study. Ten of them were selected as intact group （n=10） （fresh pig T13-L3 segment）. T1 vertebral endplate pre-injury and weight dropping technique and incremental trauma approach were used. Denis＇ type B burst fracture was produced, and ten of them were selected as unstable group （n=10）. Firstly, unstable group was decompressed by discectomy and semivertebraectomy in upper half of the vertebral body, single level was fused with lilac and U-FRONT anterior thoracolumbar system were placed between T14 and L2, as single discectomy with fixation group （n=10）. Then lower disc of injury vertebra discectomy and vertebraectomy, fused with lilac U-FRONT anterior thoracolumbar system were placed between T14 and L2, as two segment discectomy with fixation group （n=10）. The bone graft was longer 1 mm than the bone graft region. MAIN OUTCOME MEASURES： The flexion： extension, right/left lateral bending, and right/left axial rotation range of motion （ROM） of T14-L2 were measured in each group on the spinal three-motional test machine at 10 N·m. RESULTS： The flexion, extension, right/left lateral bending, and right/left axial rotation were not stable in the unstable group. ROM was significantly increased in the unstable group compared with the intact group （P 〈 0.01）. The primary stability was significantly elevated in the single discectomy with fixation and two segment discectomy with fixation groups. The flexion, extension, right/left lateral bending, and right/left axial rotation ROM were significantly reduced in the single discectomy with fixation and two segment discectomy with fixation groups compared with the unstable group （P 〈 0.05）. The flexion, extension, right/left lateral bending ROM was significantly decreased in the two groups compared with the intact group, but axial rotation ROM was significantly increased （P 〈 0.05）. Axial rotation ROM was smaller in the single discectomy with fixation group compared with the two segment discectomy with fixation group （P 〈 0.05）. CONCLUSION： Single segmental spinal interbody fusion with bisegment fixation for thoracolumbar burst fracture type B had a good immediate stability in flexion, extension, lateral bending motion. Compared with traditional partial corpectomy L1 between the caudal and cranial endplate of the adjacent vertebrae with bisegmental fixation, it had a better immediate stability in axial rotation.