Trozzi C, Kaptein B L, Garling E H, Shelyakova T, Russo A, Bragonzoni L, Martelli S
Biomechanics Laboratory, Rizzoli Orthopaedic Institute, Bologna, Italy.
Knee. 2008 Oct;15(5):396-402. doi: 10.1016/j.knee.2008.05.001. Epub 2008 Jul 16.
Model-based Roentgen Stereophotogrammetric Analysis (RSA) was recently developed for the measurement of prosthesis micromotion. Its main advantage is that markers do not need to be attached to the implants as traditional marker-based RSA requires. Model-based RSA has only been tested in uniplanar radiographic set-ups. A biplanar set-up would theoretically facilitate the pose estimation algorithm, since radiographic projections would show more different shape features of the implants than in uniplanar images. We tested the precision of model-based RSA and compared it with that of the traditional marker-based method in a biplanar set-up. Micromotions of both tibial and femoral components were measured with both the techniques from double examinations of patients participating in a clinical study. The results showed that in the biplanar set-up model-based RSA presents a homogeneous distribution of precision for all the translation directions, but an inhomogeneous error for rotations, especially internal-external rotation presented higher errors than rotations about the transverse and sagittal axes. Model-based RSA was less precise than the marker-based method, although the differences were not significant for the translations and rotations of the tibial component, with the exception of the internal-external rotations. For both prosthesis components the precisions of model-based RSA were below 0.2 mm for all the translations, and below 0.3 degrees for rotations about transverse and sagittal axes. These values are still acceptable for clinical studies aimed at evaluating total knee prosthesis micromotion. In a biplanar set-up model-based RSA is a valid alternative to traditional marker-based RSA where marking of the prosthesis is an enormous disadvantage.
基于模型的X射线立体摄影测量分析（RSA）最近被开发用于测量假体微动。其主要优点是不需要像传统的基于标记的RSA那样将标记附着在植入物上。基于模型的RSA仅在单平面放射摄影设置中进行过测试。双平面设置理论上会有助于姿态估计算法，因为放射摄影投影将显示出比单平面图像中更多的植入物不同形状特征。我们在双平面设置中测试了基于模型的RSA的精度，并将其与传统的基于标记的方法的精度进行了比较。通过对参与临床研究的患者进行两次检查，使用这两种技术测量了胫骨和股骨组件的微动。结果表明，在双平面设置中，基于模型的RSA在所有平移方向上呈现出均匀的精度分布，但在旋转方面存在不均匀误差，尤其是内外旋转的误差比绕横轴和矢状轴的旋转误差更高。基于模型的RSA比基于标记的方法精度更低，尽管对于胫骨组件的平移和旋转，除了内外旋转外，差异并不显著。对于两种假体组件，基于模型的RSA在所有平移方向上的精度均低于0.2毫米，在绕横轴和矢状轴旋转方面的精度低于0.3度。这些值对于旨在评估全膝关节假体微动的临床研究来说仍然是可以接受的。在双平面设置中，基于模型的RSA是传统的基于标记的RSA的一种有效替代方法，因为在假体上进行标记存在很大缺点。
