Centre for Imaging Sciences, The University of Manchester, Manchester M13 9PT, UK.
Wellcome Trust Centre for Cell Matrix Research, The University of Manchester, Manchester M13 9PT, UK.
Bone. 2014 Apr;61(100):64-70. doi: 10.1016/j.bone.2014.01.003. Epub 2014 Jan 14.
In total hip arthroplasty, the shape of the contra-lateral femur frequently serves as a template for preoperative planning. Previous research on contra-lateral femoral symmetry has been based on conventional hip geometric measurements (which reduce shape to a series of linear measurements) and did not take the effect of subject positioning on radiographic femur shape into account. The aim of this study was to analyse proximal femur symmetry based on statistical shape models (SSMs) which quantify global femoral shape while also adjusting for differences in subject positioning during image acquisition. We applied our recently developed fully automatic shape model matching (FASMM) system to automatically segment the proximal femur from AP pelvic radiographs to generate SSMs of the proximal femurs of 1258 Caucasian females (mean age: 61.3 SD=9.0). We used a combined SSM (capturing the left and right femurs) to identify and adjust for shape variation attributable to subject positioning as well as a single SSM (including all femurs as left femurs) to analyse proximal femur symmetry. We also calculated conventional hip geometric measurements (head diameter, neck width, shaft width and neck-shaft angle) using the output of the FASMM system. The combined SSM revealed two modes that were clearly attributable to subject positioning. The average difference (mean point-to-curve distance) between left and right femur shape was 1.0mm before and 0.8mm after adjusting for these two modes. The automatic calculation of conventional hip geometric measurements after adjustment gave an average absolute percent asymmetry of within 3.1% and an average absolute difference of within 1.1mm or 2.9° for all measurements. We conclude that (i) for Caucasian females the global shape of the right and left proximal femurs is symmetric without isolated locations of asymmetry; (ii) a combined left-right SSM can be used to adjust for radiographic shape variation due to subject positioning; and (iii) adjusting for subject positioning increases the accuracy of predicting the shape of the contra-lateral hip.
在全髋关节置换术中，对侧股骨的形状通常作为术前规划的模板。之前关于对侧股骨对称性的研究是基于传统的髋关节几何测量（将形状简化为一系列线性测量），并且没有考虑到受试者定位对股骨形状的放射学影响。本研究的目的是分析基于统计形状模型（SSM）的股骨近端对称性，该模型在量化股骨整体形状的同时，还调整了在图像采集过程中受试者定位的差异。我们应用最近开发的全自动形状模型匹配（FASMM）系统，从骨盆前后位 X 线片上自动分割股骨近端，生成 1258 名白种女性（平均年龄：61.3 岁，标准差=9.0）股骨近端的 SSM。我们使用一个综合 SSM（同时包含左右股骨）来识别和调整由于受试者定位而导致的形状变化，以及一个单独的 SSM（包含所有股骨作为左侧股骨）来分析股骨近端对称性。我们还使用 FASMM 系统的输出计算传统的髋关节几何测量（股骨头直径、颈宽、干宽和颈干角）。综合 SSM 显示出两个明显归因于受试者定位的模式。在调整这两个模式之前，左右股骨形状之间的平均差异（平均点到曲线距离）为 1.0mm，调整后为 0.8mm。调整后的传统髋关节几何测量的自动计算给出了所有测量值的平均绝对不对称百分比为 3.1%，平均绝对差值为 1.1mm 或 2.9°。我们得出结论：（i）对于白种女性，左右股骨近端的整体形状是对称的，没有孤立的不对称部位；（ii）一个综合的左右 SSM 可以用于调整由于受试者定位导致的放射学形状变化；（iii）调整受试者定位可以提高预测对侧髋关节形状的准确性。
