Rousseau Marc-Antoine, Bradford David S, Bertagnoli Rudi, Hu Serena S, Lotz Jeffery C
Department of Orthopaedic Surgery, University of California San Francisco, San Francisco, CA 94143, USA.
Spine J. 2006 May-Jun;6(3):258-66. doi: 10.1016/j.spinee.2005.07.004.
Total disc replacement is a novel approach for dynamically stabilizing a painful intervertebral segment. While this approach is gaining popularity, and several types of implants are used, the effect of disc arthroplasty on lumbar biomechanics has not been widely reported. Consequently, beneficial or adverse effects of this procedure may not be fully realized, and data for kinematic optimization are unavailable.
To characterize kinematic and load transfer modifications at L5/S1 secondary to joint replacement.
A human cadaveric biomechanical study in which the facet forces and instant axes of rotation (IAR) were measured for different spinal positions under simulated weightbearing conditions before and after total disc replacement at L5/S1 using semiconstrained (3 degrees of freedom [DOF]; Prodisc) and unconstrained (5 DOF; Charité) articulated implants.
Twelve radiographically normal human cadaveric L5/S1 joints (age range 45-64 years) were tested before and after disc replacement using Prodisc II implants (Spine Solutions, Paoli, PA) in six specimens and SB Charité III (Johnson & Johnson, New Brunswick, NJ) in six other specimens. Semiconstrained fixtures in combination with a servo-hydraulic materials testing system subjected the test specimens to a physiologic combination of compression and anterior shear. Multiple intervertebral positions were studied and included up to 6 degrees of flexion, extension, and lateral bending. The IAR was calculated for every 3-degree intervals, and the force through the facet joints was simultaneously measured using flexible intra-articular sensors. Data were analyzed using repeated-measures analysis of variance.
During flexion/extension, the average IAR positions and directions were not significantly modified by implantation with the exception that the IAR was higher relative to S1 end plate with the Charité (p=.028). The IAR had a vertically oriented centrode throughout flexion/extension with the Prodisc (p<.001) and the Charité (p<.016). The centrode tended to be greater with the Prodisc. There was a trend that the facet force was decreased throughout flexion/extension for the Prodisc; however, this was statistically significant only at 6 degrees extension (27%, p=.013). In lateral bending, the IAR was significantly modified by Prodisc replacement, with a decreased inclination relative to S1 end plate, (ie, increased coupled axial rotation). While the IAR moved in the horizontal plane toward the side of bending, this effect was more pronounced with the Prodisc. The ipsilateral facet force was significantly increased in 6 degrees lateral bending with the Charité (85%; p=.001).
The degree of constraint affects post-implantation kinematics and load transfer. With the Prodisc (3 DOF), the facets were partially unloaded, though the IAR did not match the fixed geometrical center of the UHMWPE. The latter observation suggests joint surface incongruence is developed during movement. With the Charité (5 DOF), the IAR was less variable, yet the facet forces tended to increase, particularly during lateral bending. These results highlight the important role the facets play in guiding movement, and that implant constraint influences facet/implant synergy. The long-term consequences of the differing kinematics on clinically important outcomes such as wear and facet arthritis have yet to be determined.
全椎间盘置换术是一种用于动态稳定疼痛椎间盘节段的新方法。虽然这种方法越来越受欢迎，并且使用了几种类型的植入物，但椎间盘置换术对腰椎生物力学的影响尚未得到广泛报道。因此，该手术的有益或不利影响可能无法完全实现，并且缺乏用于运动学优化的数据。
描述L5/S1节段关节置换术后的运动学和负荷传递变化。
一项人体尸体生物力学研究，在L5/S1节段使用半限制型（3个自由度[DOF]；Prodisc）和非限制型（5个自由度；Charité）铰接式植入物进行全椎间盘置换前后，在模拟负重条件下测量不同脊柱位置的小关节力和瞬时旋转轴（IAR）。
对12个放射学正常的人体尸体L5/S1关节（年龄范围45-64岁）进行测试，其中6个标本使用Prodisc II植入物（Spine Solutions，Paoli，PA），另外6个标本使用SB Charité III（强生公司，新不伦瑞克，NJ）进行椎间盘置换前后的测试。半限制型固定装置与伺服液压材料测试系统相结合，使测试标本承受压缩和前剪切的生理组合。研究了多个椎间位置，包括高达6度的屈曲、伸展和侧方弯曲。每3度间隔计算一次IAR，并使用柔性关节内传感器同时测量通过小关节的力。使用重复测量方差分析对数据进行分析。
在屈伸过程中，除了Charité植入物相对于S1终板的IAR较高外（p=0.028），植入后平均IAR位置和方向没有显著改变。使用Prodisc（p<0.001）和Charité（p<0.016）时，IAR在整个屈伸过程中具有垂直定向的中心轨迹。Prodisc的中心轨迹往往更大。Prodisc在整个屈伸过程中，小关节力有下降趋势；然而，仅在6度伸展时具有统计学意义（27%，p=0.013）。在侧方弯曲时Prodisc置换显著改变了IAR，相对于S1终板的倾斜度降低（即耦合轴向旋转增加）。虽然IAR在水平面内向弯曲侧移动，但Prodisc的这种影响更明显。使用Charité时，在6度侧方弯曲时同侧小关节力显著增加（8%；p=0.001）。
限制程度影响植入后的运动学和负荷传递。使用Prodisc（3个自由度）时，小关节部分卸载，尽管IAR与超高分子量聚乙烯的固定几何中心不匹配。后一观察结果表明在运动过程中关节表面不一致。使用Charité（5个自由度）时，IAR变化较小，但小关节力倾向于增加，特别是在侧方弯曲时。这些结果突出了小关节在引导运动中所起的重要作用，并且植入物限制影响小关节/植入物协同作用。不同运动学对磨损和小关节关节炎等临床重要结果的长期影响尚未确定。
