三维模型中踝关节中心定位的研究

目的　应用不同方法在三维重建模型上定位踝关节中心，并判断各方法的可行性，准确定位踝关节中心，进而为三维模拟下肢膝关节置换术提供形态学基础。 方法　对33例正常成人踝关节行CT扫描，数据导入三维重建软件Mimics，重建出踝关节三维立体模型，在逆向工程软件Geomagic Studio中分别采用距骨顶部中点（A点）、距骨顶部点云质心（B点）和内外踝间距中点（C点）3种方法对踝关节中心进行定位，并在冠状面上对三中心点之间的距离进行测量，应用统计软件SPSS对数据进行分析。 结果　成功建立了踝关节的三维立体模型，并用不同方法定位出踝关节中心。测量结果显示A点与B点之间的距离为(1.058±0.741)mm， B点与C点之间的距离为(1.684±1.283)mm， A点与C点之间的距离为(1.484±1.040)mm。且每个中心点之间的距离差异不具有显著性(P>0.05)。 结论　基于三维重建模型上的踝关节中心定位方法具有可行性，且与二维平面上的定位相比稳定性更高，其中距骨顶部点云质心作为踝关节中心较其他两种方法更简便易行。

Research on positioning methods of the ankle joint in three-dimensional model

Objective　To find out the exact center of ankle joint position, this study use different methods in three-dimensional(3D) reconstruction model, and determine the feasibility of these methods. Then provide morphological basis for the 3D simulation of lower limb knee arthroplasty.　Methods　33 cases of normal adult ankle joints were scanned by CT. The data was imported into three-dimensional reconstruction software. 3D reconstruction software was used to reconstruct the 3D model of the ankle joint; the midpoint of top talus (point A)、the centroid of point cloud in top talus(point B) and the midpoint between the medial malleolus and lateral malleolus(point C) respectively were used for positioning of the center of the ankle joint in the reverse engineering software, and measurement of the distance among these three points in the coronal plane. Data analysis was performed using statistics package for social science (SPSS).　Results　The 3D model of the ankle joint was successfully established, and the center of ankle joint was located using different positioning methods. The measurement results showed: The average distance between point A and point B was (1.058±0.714)mm; The average distance between point B and point C was (1.684±1.283)mm; The average distance between point A and point C was (1.484±1.040)mm. And the distance difference between each group was not statistically significant (P>0.05).　Conclusion　Location of center of the ankle joint based on 3D reconstruction is feasible, and more stable than positioning methods in two-dimensional plane. And the centroid of point cloud in top talus as the talus center of ankle joint are more convenient than the other two methods.