Paradigm Spine, GmbH, Eisenbahnstrasse 84, D-78573 Wurmlingen, Germany.
Spine J. 2010 Mar;10(3):244-51. doi: 10.1016/j.spinee.2009.10.010. Epub 2009 Dec 11.
The in vivo loading environment of load-bearing implants is generally largely unknown. Loads are typically approximated from cadaver tests or biomechanical calculations for the preclinical assessment of a device's safety and efficacy.
To determine the actual in vivo loading environment of an elastic interlaminar-interspinous implant (Coflex).
A retrospective radiographic study to noninvasively measure the in vivo implant loads of 176 patients.
For this study, neutral, flexion, and extension radiographs were quantitatively analyzed using validated image analysis technology. The angle between the Coflex arms was measured for each radiograph and statistically evaluated. Separately, the Coflex implant was characterized using mechanical test data and finite element analysis, which resulted in a load-deformation formula that describes the implant load as a function of its size and elastic deformation. Using the formula and the elastic implant deformation data obtained from the radiographic analysis, the exact implant load was calculated for each patient and each posture. For statistical analysis, the patients were grouped by indication and procedure, which resulted in 12 different groups. The determined loads were compared with the strength of the posterior lumbar spinal elements obtained from the literature and with the static and dynamic mechanical limits of the Coflex interlaminar-interspinous implant.
The force data were independent of implant size, diagnosis (with one exception), number of levels of the decompression procedure, number of levels of implantations (one or two), and follow-up time. The median compressive force acting on the Coflex implant was found to be 45.8 N. The maximum load change between flexion and extension was 140 N; the maximum overall load exceeded 239 N in extension.
The average loads exerted by the Coflex implant on the spinous process and lamina are 11.3% and 7.0% of their respective static failure load. The implant fatigue strength is significantly higher than the measured median force, which explains the extremely rare observation of a Coflex fatigue failure.
承重植入物的体内负荷环境通常很大程度上是未知的。负荷通常是根据尸体测试或生物力学计算来近似的，用于临床前评估设备的安全性和有效性。
确定弹性椎间板间棘突间植入物（Coflex）的实际体内负荷环境。
一项回顾性放射学研究，旨在非侵入性地测量 176 名患者的体内植入物负荷。
在这项研究中，使用经过验证的图像分析技术对中立位、前屈位和后伸位的 X 光片进行定量分析。对每个 X 光片的 Coflex 臂之间的角度进行测量，并进行统计学评估。另外，使用机械测试数据和有限元分析对 Coflex 植入物进行了特征描述，得到了一个描述植入物负荷与其尺寸和弹性变形之间关系的负荷-变形公式。利用公式和从放射学分析中获得的弹性植入物变形数据，计算出每个患者和每个姿势的精确植入物负荷。为了进行统计学分析，根据适应证和手术程序将患者分组，共分为 12 个不同的组。将确定的负荷与文献中获得的腰椎后部结构的强度以及 Coflex 椎间板间棘突间植入物的静态和动态力学极限进行比较。
力数据与植入物尺寸、诊断（仅有一个例外）、减压手术的节段数、植入物的节段数（一个或两个）和随访时间无关。发现作用于 Coflex 植入物的压缩力中位数为 45.8N。前屈和后伸之间的最大负荷变化为 140N；后伸时总最大负荷超过 239N。
Coflex 植入物对棘突和椎板施加的平均负荷分别为其静态失效负荷的 11.3%和 7.0%。植入物的疲劳强度明显高于测量的中值力，这解释了极为罕见的 Coflex 疲劳失效现象。
