采用Y形前路解剖型钢板固定髋臼四方区骨折的生物力学研究

目的评估采用Y形前路解剖型钢板固定涉及前柱的髋臼四方区骨折的生物力学,为该新型钢板用于临床治疗提供客观的力学依据。方法将6具新鲜尸体骨盆标本随机分为3组,骨折模型构建前保持关节结构组织完整设为对照组;制作涉及前柱的髋臼四方区骨折模型,分别采用经典的重建钢板和Y形前路解剖型钢板固定,进行实验应力学测试和性能评估。结果髋臼四方区骨折采用Y形前路解剖型钢板内固定的强度比重建钢板内固定高19％,刚度提高18％,髋臼骨折分离移位降低10％,髋臼骨折负重接触面积提高18％,同时扭转强度和刚度均相应提高17％和19％,差异均有统计学意义（P〈O．05）。结论髋臼四方区骨折采用Y形前路解剖型钢板固定较采用经典重建钢板固定具有更强的力学稳定性．为临床治疗髋臼四方区骨折提供了一种新的内固定选择。     

Evaluation of a polyaxial angle-stable volar plate in a distal radius C-fracture model--a biomechanical study

Introduction

Polyaxial angle-stable plating is thought to be particularly beneficial in the management of complex intra-articular fractures of the distal radius. The purpose of the present study was to investigate whether the technique provides stability to match that of conventional (fixed-angle) angle-stable constructs.

Material and methods

In seven pairs of human cadaver radii, an Arbeitsgemeinschaft für Osteosynthese (AO) 23 C2.1 intra-articular fracture was created. One radius of each pair received a juxta-articular 2.4-mm locking compression plate (LCP) Volar Distal Radius Plate, whilst the contralateral one received a 2.4-mm Variable Angle Locking Compression Plate (LCP) Two-Column Volar Distal Radius Plate (both plates: Synthes, Oberdorf, Switzerland). Parameters tested were construct stiffness (static axial loading with 150 N), range of motion and secondary loss of reduction (dynamic 150 N axial loading over 5000 cycles). Stiffness and range of motion were measured both pre- and post-cycling.

Results

The polyaxial constructs were significantly stiffer, both before and after cyclic testing. However, the two-column plates showed a significant loss of stiffness during cyclic testing. The range of motion was significantly greater, both initially and at the end of cyclic testing, in the fixed-angle constructs. The conventional constructs had significantly greater secondary loss of reduction.

Conclusion

The polyaxial two-column plate tested in this study provides a biomechanically sound construct for the management of intra-articular fractures of the distal radius.     

A prospective study of anterior cervical spondylodesis in intervertebral disc disorders

Summary In 1977, a prospective study of anterior cervical fusion was started in cases of intervertebral disc disorders with neuropathy and/or myelopathy up to 1986. A total of 193 patients was operated upon, of whom 179 were available for this study, with a mean follow-up time of 10.4 years (6-14 years) and a mean age of 51 years (28–76). There was an extensive record for every patient according to the protocol. The indication for operation was decided upon by an orthopaedic surgeon and a neurologist and was defined as discopathy with progressive neurological disorders, which did not respond to conservative therapy. The wearing of a stiff collar for 6 weeks during which time there was a improvement of the neurological symptoms was a strict precondition for the operation. Up to 5 levels were fused, with a mean of 2.3 levels per patient. During the operation a discography was performed on the symptomatic level(s) and the adjacent levels. All levels with positive discopathy were fused. In this longterm study the overall percentage of excellent and good results was about 82%. The results of fusions involving more than two levels were very encouraging.     

Biomechanical study of anterior spinal instrumentation configurations

The biomechanical impact of the surgical instrumentation configuration for spine surgery is hard to evaluate by the surgeons in pre-operative situation. This study was performed to evaluate different configurations of the anterior instrumentation of the spine, with simulated post-operative conditions, to recommend configurations to the surgeons. Four biomechanical parameters of the anterior instrumentation with simulated post-operative conditions have been studied. They were the screw diameter (5.5–7.5 mm) and its angle (0°–22.5°), the bone grip of the screw (mono–bi cortical) and the amount of instrumented levels (5–8). Eight configurations were tested using an experimental plan with instrumented synthetic spinal models. A follower load was applied and the models were loaded in flexion, torsion and lateral bending. At 5 Nm, average final stiffness was greater in flexion (0.92 Nm/°) than in lateral bending (0.56 Nm/°) and than in torsion (0.26 Nm/°). The screw angle was the parameter influencing the most the final stiffness and the coupling behaviors. It has a significant effect (p ≤ 0.05) on increasing the final stiffness for a 22.5° screw angle in flexion and for a coronal screw angle (0°) in lateral bending. The bi-cortical bone grip of the screw significantly increased the initial stiffness in flexion and lateral bending. Mathematical models representing the behavior of an instrumented spinal model have been used to identify optimal instrumentation configurations. A variation of the angle of the screw from 22.5° to 0° gave a global final stiffness diminution of 13% and a global coupling diminution of 40%. The screw angle was the most important parameter affecting the stiffness and the coupling of the instrumented spine with simulated post-operative conditions. Information about the effect of four different biomechanical parameters will be helpful in preoperative situations to guide surgeons in their clinical choices.     

前路腰椎椎体间融合术的生物力学研究

前路腰椎椎体间融合术(ALIF)具有诸多优势,临床应用越来越多.关于ALIF的生物力学稳定性研究国外开展较多,但结果并不完全一致.应根据不同需要合理选择ALIF试验模型,人类尸体,动物尸体、有限元模型、其他替代模型等各有优缺点.单纯ALIF术后椎间获得即刻稳定性是根据"撑开一压缩"原理.前路椎间植入融合器后能够增加除了后伸动作以外的其他各方向稳定性,目前大多数关于ALIF的生物力学测试均针对即刻稳定性,然而融合器植入椎间隙后纤维环弹性逐渐丧失及融合器陷入终板内均会使椎间稳定性逐渐降低,因此椎间融合稳定性还取决于界面骨长入速度等术后因素.影响ALIF稳定性的因素有预负荷、辅助内固定、相邻椎体骨质量等.     

新型寰枢椎后路动态固定系统的生物力学评价

目的测试并评价新型寰枢椎后路动态固定系统的生物力学性能。方法新鲜成人枕颈标本（C0-4）8例,分成4组：完整状态组、寰枢椎不稳状态组、寰枢椎后路动态固定状态组和寰枢椎后路椎弓根螺钉固定状态组。通过加载1.50 N·m的力矩,对4组标本C1/C2、C2/C3节段的前屈/后伸,左/右侧弯和左/右旋转等6种运动方式下的运动范围（range of movement,ROM）及稳定性指数（stability index,SI）进行测试。结果采用新型寰枢椎后路动态固定系统后,C1/C2、C2/C3节段的ROM与正常完整标本相比较,差异无统计学意义（P〉0.05）;而采用常规椎弓根螺钉固定与动态固定法相比,C1/C2、C2/C3节段的ROM差异有统计学意义（P〈0.001）。采用寰枢椎后路动态固定系统固定与采用后路椎弓根螺钉固定,C1/C2SI均上升,与完整状态组相比差异均有统计学意义,分别为（P〈0.05）和（P〈0.001）。C2/C3测试结果显示,采用动态固定时SI分别上升为109%、107%和112%;而采用椎弓根螺钉固定,三维运动范围SI反而分别下降为77%、71%和87%,比动态固定SI分别低29%、34%和22%,差异具有统计学意义（P〈0.001）。结论新型寰枢椎后路动态固定系统既可维持寰枢椎的部分旋转功能,又可达到坚固固定的稳定性,同时能够有效地减少对邻近节段的影响,具有良好的研究前景。     

Biomechanical testing of an artificial cervical joint and an anterior cervical plate

An in vitro biomechanical study was conducted to determine the effects of fusion and nonfusion anterior cervical instrumentation on cervical spine biomechanics in a multilevel human cadaveric model. Three spine conditions were studied: harvested, single-level artificial cervical joint, and single-level graft with anterior cervical plate. A programmable testing apparatus was used that replicated physiologic flexion/extension and lateral bending. Measurements included vertebral motion, applied load, and bending moments. Relative rotations at the superior, implanted, and inferior motion segment units (MSUs) were normalized with respect to the overall rotation of those three MSUs and compared using a one-way analysis of variance (P < 0.05). Application of an anterior cervical plate decreased motion across the fusion site relative to the harvested and artificial joint spine conditions. The reduced motion was compensated for by an increase in motion at the adjacent segments. Use of an artificial cervical joint did not alter the motion patterns at either the instrumented level or the adjacent segments compared with the harvested condition for all modes of testing.     

Spontaneous anterior atlanto-axial subluxation--a case story]

In this study, a case of 4.5 years' old girl with spontaneous dislocation of C1/C2 vertebrae probably due to congenital defect of C1-hypoplasia of the atlas anterior arch is presented. Treatment consisted of skull traction and slow reposition followed by surgical spinodesis C1 and C2. During examination after 1 year follow up period, patient was in good clinical condition, without any complaints. On radiograms the cervical spine was stable and of correct shape.