计算机辅助确定下肢机械轴线在全膝关节置换术中的应用

Establishing lower-extremity mechanical axis by computer-aided design and its application in total knee arthroplasty

目的探讨计算机辅助确定下肢机械轴线在全膝关节置换术中的价值。方法36例拟行全膝关节置换术的患者随机分为两组，每组18例。导航模板组采用计算机辅助设计导航模板方法确定下肢机械轴线，髓内定位组采用传统髓内定位方法。导航模板组术前将髋、膝及踝关节螺旋CT扫描图像和下肢全长X线图像导入三维重建软件，重建髋、膝、踝关节模型并修正负重状态。将重建模型文件导入逆向工程软件，构建股骨头、膝关节、胫骨平台、踝关节中心，确定股骨和胫骨机械轴线。扫描全膝关节假体，导入逆向工程软件。将导航模板组重建后的髋、膝、踝模型与假体模型进行匹配。按照下肢机械轴线设计与股骨远端匹配的定位截骨平面的导航模板及胫骨近端机械轴线髓内定位通道，通过快速成型机制作模板实体用于全膝关节置换手术操作。术后通过CT扫描及三维重建分析比较两组手术的准确性。结果导航模板组手术时间（46．8±9．1）min，髓内定位组（57．5±12．3）min，差异有统计学意义。导航模板组假体冠状股骨角、冠状胫骨角及胫骨后倾角分别为89．4°±1．5°、89．3°±1．4°、6．8。±1．6°，髓内定位组分别为87.3°±3．8°、88．1°±1．9°、10．9°±4．6°，差异有统计学意义。术后12个月HSS膝关节评分导航模板组和髓内定位组分别为（82．9±16．8）分和（72．8±10．9）分，差异有统计学意义。结论计算机辅助确定力线设计的截骨模板具有较高的精确性，可为全膝关节置换术提供更加精确的截骨方式，操作简便。

Objective To evaluate the value of computer-aided establishing lower-extremity mechanical axis in total knee arthroplasty using digital technology. Methods 36 cases of patients with TKA were randomly divided into the computeraided design of navigation template （NT） group and conventional intramedullary positioning （CIP） group. The lower limb length X- ray images were obtained preoperatively. Three-dimensional （3D） CT scanning images of hip, knee and ankle data were obtained in NT group. X-ray image and CT datum were transferred into the 3D reconstruction software. 3D bone models of hip, knee, ankle and modified loading were reconstructed, and saved in STL format. Then the 3D models were imported into reverse engineering software. On the 3D reconstruction models, centers of the femoral head, the knee, tibia and the ankle were defined, and then the mechanical axis of lower limb were determined. After matching the models of bone and prosthesis, the navigational templates were designed according the mechanical axis of lower limb. The navigational templates produced an accurate model using a rapid prototyping technique to assist patients in TKA. CT scans were performed postoperatively to evaluate the accuracy of the two TKA methods. Results The average operative time of the NT group procedures was 46.8±9.1 min, shorter than those with conventional procedures （57.5±12.3 min）. The coronal femoral angle, coronal tibial angle and posterior tibial slope were 89.4°_±1.5°, 89.3°±1.4°, 6.8°±1.6° in NT group, 87.30±3.8°, 88.1°±1.9°, 10.9°±4.6° in CIP group respectively. Statistically significant differences were found between them. The HSS scores were 82.9±16.8 and 72.8±10.9 respectively at the 12th month after the opera- tion, and statistically significant differences were found between them. Conclusion The navigation template produced through mechanical axis of lower extremity may provide a relative accurate and simple osteotomy method for total knee arthroplasty.