Perrin Nathalie, Stindel Eric, Roux Christian
Laboratoire de Traitement de l'Information Médicale (LaTIM), Brest, France.
Comput Aided Surg. 2005 Sep-Nov;10(5-6):301-9. doi: 10.3109/10929080500389845.
This study analyzed the influence of the acquisition method in image-free computer-assisted total knee arthroplasty (CAS-TKA), and the reproducibility of implant planning using BoneMorphing, a 3D morphometric model obtained by a 3D-to-3D elastic registration of statistical models to sparse point clouds acquired directly on the bone surface with a pointer.
Five surgeons (one expert, four trainees) each performed a CAS-TKA hybrid protocol based on morphometric models and landmarks on a cadaveric knee 10 times. In addition, several additional landmarks were digitized during each acquisition. The reproducibility of the implant positioning and sizing, as determined by an implant planning algorithm with morphometric models, was compared to direct digitization accuracy.
Femoral and tibial implant positioning parameters with the hybrid protocol resulted in intra-surgeon standard deviations (SDs) of less than+/-1.4 degrees for rotation and 1.9 mm for translation for all surgeons in all directions except for tibial axial rotation (the only parameter determined by a digitized landmark and not recomputed in the 3D model). The variability in individual landmark digitization varied from 2 to 5 mm SD for certain landmarks, with ranges of 15-25 mm across all surgeons. The comparison study showed an improvement in femoral rotation reproducibility with the morphometric model when using the posterior condylar axis. Tibial implant reproducibility for each method was comparable, with the morphometric model giving better results in well-digitized areas such as the tibial plateau.
A CAS-TKA protocol based on a deformed statistical model offers reproducible implant positioning. Some landmarks, such as distal condyles, show sufficient reproducibility in the direction of interest, while others, such as the anterior tibial tubercle, can lead to hazardous implant positioning. This should be taken into consideration when designing a CAS-TKA system with bony landmarks. In areas where a sufficient number of points have been digitized with good coverage, such as on the distal and posterior femoral condyles or the tibial plateau areas, the information derived from the 3D model is more accurate and reproducible than that derived from digitization. Good training and a guiding user interface are essential to guarantee coverage quality.
本研究分析了无图像计算机辅助全膝关节置换术（CAS-TKA）中采集方法的影响，以及使用BoneMorphing进行植入物规划的可重复性。BoneMorphing是一种通过将统计模型与用指针直接在骨表面采集的稀疏点云进行三维到三维弹性配准而获得的三维形态计量模型。
五名外科医生（一名专家、四名实习生）每人基于形态计量模型和标志点对一具尸体膝关节进行10次CAS-TKA混合操作流程。此外，在每次采集过程中还对几个额外的标志点进行了数字化处理。将通过形态计量模型的植入物规划算法确定的植入物定位和尺寸的可重复性与直接数字化精度进行比较。
对于所有外科医生，混合操作流程的股骨和胫骨植入物定位参数在所有方向上的术者内标准差（SD），除胫骨轴向旋转（唯一由数字化标志点确定且未在三维模型中重新计算的参数）外，旋转小于±1.4度，平移小于1.9毫米。某些标志点的个体标志点数字化变异性的标准差在2至5毫米之间，所有外科医生的范围为15至25毫米。比较研究表明，使用髁间后轴时，形态计量模型可提高股骨旋转的可重复性。每种方法的胫骨植入物可重复性相当，形态计量模型在胫骨平台等数字化良好的区域效果更好。
基于变形统计模型的CAS-TKA操作流程可提供可重复的植入物定位。一些标志点，如髁远端，在感兴趣的方向上显示出足够的可重复性，而其他标志点，如胫骨前结节，可能导致植入物定位危险。在设计带有骨性标志点的CAS-TKA系统时应考虑到这一点。在已用良好覆盖范围进行数字化处理的足够数量点的区域，如股骨髁远端和后髁或胫骨平台区域，从三维模型获得的信息比从数字化获得的信息更准确且可重复。良好的培训和引导用户界面对于保证覆盖质量至关重要。
