University of Basel, 4056 Basel, Switzerland.
Biomed Eng Online. 2011 Jul 17;10:60. doi: 10.1186/1475-925X-10-60.
Dynamic three-dimensional (3D) deformation of the pelvic bones is a crucial factor in the successful design and longevity of complex orthopaedic oncological implants. The current solutions are often not very promising for the patient; thus it would be interesting to measure the dynamic 3D-deformation of the whole pelvic bone in order to get a more realistic dataset for a better implant design. Therefore we hypothesis if it would be possible to combine a material testing machine with a 3D video motion capturing system, used in clinical gait analysis, to measure the sub millimetre deformation of a whole pelvis specimen.
A pelvis specimen was placed in a standing position on a material testing machine. Passive reflective markers, traceable by the 3D video motion capturing system, were fixed to the bony surface of the pelvis specimen. While applying a dynamic sinusoidal load the 3D-movement of the markers was recorded by the cameras and afterwards the 3D-deformation of the pelvis specimen was computed. The accuracy of the 3D-movement of the markers was verified with 3D-displacement curve with a step function using a manual driven 3D micro-motion-stage.
The resulting accuracy of the measurement system depended on the number of cameras tracking a marker. The noise level for a marker seen by two cameras was during the stationary phase of the calibration procedure ± 0.036 mm, and ± 0.022 mm if tracked by 6 cameras. The detectable 3D-movement performed by the 3D-micro-motion-stage was smaller than the noise level of the 3D-video motion capturing system. Therefore the limiting factor of the setup was the noise level, which resulted in a measurement accuracy for the dynamic test setup of ± 0.036 mm.
This 3D test setup opens new possibilities in dynamic testing of wide range materials, like anatomical specimens, biomaterials, and its combinations. The resulting 3D-deformation dataset can be used for a better estimation of material characteristics of the underlying structures. This is an important factor in a reliable biomechanical modelling and simulation as well as in a successful design of complex implants.
骨盆骨骼的动态三维（3D）变形是复杂矫形肿瘤植入物成功设计和长期使用的关键因素。目前的解决方案对患者来说往往不是很有希望；因此，测量整个骨盆的动态 3D 变形以获得更真实的数据集，从而为更好的植入物设计提供更好的数据是很有意义的。因此，我们假设是否有可能将材料试验机与用于临床步态分析的 3D 视频运动捕捉系统相结合，以测量整个骨盆标本的亚毫米变形。
将骨盆标本放置在材料试验机上的站立位置。将可通过 3D 视频运动捕捉系统跟踪的无源反射标记物固定在骨盆标本的骨表面上。当施加动态正弦载荷时，标记物的 3D 运动由摄像机记录，然后计算骨盆标本的 3D 变形。使用手动驱动的 3D 微动台，通过带有阶跃函数的 3D 位移曲线验证标记物 3D 运动的准确性。
测量系统的测量精度取决于跟踪标记物的摄像机数量。在标定程序的静止阶段，两个摄像机跟踪的标记物的噪声水平为±0.036mm，如果由 6 个摄像机跟踪，则为±0.022mm。3D 微动台执行的可检测 3D 运动小于 3D 视频运动捕捉系统的噪声水平。因此，该设置的限制因素是噪声水平，这导致动态测试设置的测量精度为±0.036mm。
这种 3D 测试设置为大范围材料（如解剖标本、生物材料及其组合）的动态测试开辟了新的可能性。生成的 3D 变形数据集可用于更好地估计基础结构的材料特性。这是可靠的生物力学建模和模拟以及复杂植入物成功设计的重要因素。
