Michaut M, Beaufils P, Galaud B, Abadie P, Boisrenoult P, Fallet L
Service de chirurgie-orthopédique, centre hospitalier de Versailles, 177, rue de Versailles, 78157 Le Chesnay, France.
Rev Chir Orthop Reparatrice Appar Mot. 2008 Oct;94(6):580-4. doi: 10.1016/j.rco.2008.03.038. Epub 2008 May 27.
Accurate implantation of the prosthesis components is a prognostic factor for long-term total knee arthroplasty survival as it reduces wear and loosening failure. Computer-assisted navigation systems have proved to produce accurate bone cuts orthogonal to the mechanical axis. Proper rotational alignment of the femoral component is one of the requirements for optimal positioning of the femoral prosthesis. The posterior bicondylar axis of the femoral prosthesis should therefore be parallel to the transepicondylar axis. The purpose of the present study was to determine whether computer-assisted navigation provides an accurate rotational alignment of the femoral implant, when preoperatively defined with CT scan.
This prospective study, carried out between December 2003 and June 2005, included 70 patients of average age 74 years old (range 57-85) who underwent primary total knee arthroplasty, with a SAL prosthesis (Zimmer). Preoperative investigations with computed tomography scanning produced accurate measurements of distal epiphyseal femoral torsion (DEFT). The posterior bicondylar axis was found to be a reliable landmark for the rotational orientation of the femoral cutting-guide during bone-cuts. The rotational orientation of the cutting-guide was based on the preoperative CT data. A three-month follow-up CT scan was carried out to evaluate final rotational position of the femoral component.
The mean DEFT evaluated on the preoperative CT scan was 6.9+/-2.9 degrees . The mean rotational orientation of the cutting guide was 4.8+/-2 degrees . The mean postoperative measurement of DEFT was 1.56+/-2.7 degrees . The mean adjustment of DEFT was 5.34 degrees . Adopting a +/- 2 degrees cutoff, 77 % of patients achieved acceptable alignment within +/- 2 degrees compared with our objectives. These findings were compared to a previous series of 34 cases using an arbitrary 3 degrees standardized rotation of the femoral component and following an identical radiological protocol. Among the knees, 44% reported alignment within +/- 2 degrees .
When femoral and tibial bone cuts are performed independently, conventional instrumentation techniques seem insufficient to adapt patient's specific anatomy and prove inadequate to provide precise rotational alignment of the femoral component. Computed tomography scan is a reliable mean to produce precise preoperative measurements for proper DEFT. Moreover, it allows accurate postoperative control of the implant positioning. Other studies have documented a higher degree of precision in the rotational alignment of the femoral component with computed navigation systems in comparison to conventional instrumentation. However, in such studies, rotational alignment was always determined by computer navigation, and based on a controversial intraoperative identification (epicondyles and Whiteside's line referencing). We believe that preoperative CT scanning is a more favourable method. Actually, 77% of the cases reported satisfactory rotational alignment of the femoral component using this technique.
假体组件的精确植入是全膝关节置换长期存活的一个预后因素，因为它可减少磨损和松动失败。计算机辅助导航系统已被证明能产生与机械轴正交的精确截骨。股骨组件的正确旋转对线是股骨假体最佳定位的要求之一。因此，股骨假体的后双髁轴应与经髁轴平行。本研究的目的是确定在术前通过CT扫描定义时，计算机辅助导航是否能提供股骨植入物的精确旋转对线。
这项前瞻性研究于2003年12月至2005年6月进行，纳入了70例平均年龄74岁（范围57 - 85岁）接受初次全膝关节置换的患者，使用SAL假体（ Zimmer公司）。术前通过计算机断层扫描进行的检查对股骨远端骨骺扭转（DEFT）进行了精确测量。后双髁轴被发现是截骨过程中股骨截骨导向器旋转方向的可靠标志。截骨导向器的旋转方向基于术前CT数据。术后三个月进行CT扫描以评估股骨组件的最终旋转位置。
术前CT扫描评估的平均DEFT为6.9±2.9度。截骨导向器的平均旋转方向为4.8±2度。术后DEFT的平均测量值为1.56±2.7度。DEFT的平均调整值为5.34度。采用±2度的截断值，与我们的目标相比，77%的患者在±2度范围内实现了可接受的对线。这些结果与之前一系列34例使用股骨组件任意3度标准化旋转并遵循相同放射学方案的病例进行了比较。在这些膝关节中，44%报告对线在±2度范围内。
当股骨和胫骨截骨独立进行时，传统的器械技术似乎不足以适应患者的特定解剖结构，并且被证明不足以提供股骨组件的精确旋转对线。计算机断层扫描是一种可靠的方法，可用于为适当的DEFT产生精确的术前测量。此外，它还能对植入物位置进行精确的术后控制。其他研究记录了与传统器械相比，计算机导航系统在股骨组件旋转对线方面具有更高的精度。然而，在这些研究中，旋转对线总是由计算机导航确定，并基于有争议的术中识别（髁和Whiteside线参考）。我们认为术前CT扫描是一种更有利的方法。实际上，使用该技术77%的病例报告股骨组件的旋转对线令人满意。
