Three-dimensional reconstruction method for measuring the knee valgus angle of the femur in northern Chinese adults

The purpose of this study was to establish a method for measuring the knee valgus angle from the anatomical and mechanical axes on three-dimensional reconstruction imaging models, and to use this method for estimating an average knee valgus angle value for northern Chinese adults. Computed tomographic angiography data in DICOM format for 128 normal femurs from 64 adult subjects were chosen for analysis. After the femur images were subjected to three-dimensional reconstruction, the deepest point in the intercondylar notch (point A), the midpoint of the medullary cavity 20 cm above the knee-joint line (point B), and the landmark of the femoral head rotation center (point C) were identified on each three-dimensional model. The knee valgus angle was defined as the angle enclosed by the distal femoral anatomical axis (line AB) and the femoral mechanical axis (line AC). The average (mean±SD) of knee valgus angle for the 128 femurs was 6.20°±1.20° (range, 3.05° to 10.64°). Significant positive correlations were found between the knee valgus angles of the right and left sides and between the knee valgus angle and age. During total knee arthroplasty, choosing a valgus cut angle of approximately 6° may achieve a good result in reestablishing the natural mechanical alignment of the lower extremity for patients of northern Chinese ethnicity. Larger valgus cut angles should be chosen for older patients.概要研究目的利用三维重建影像模型获取膝外翻角, 并通过使用这种方法来测量中国北方成人膝外翻角的平均估计值。创新要点本研究所获取的膝外翻角平均值对于在中国北方人群进行膝关节置换术时有着重要的参考意义, 新的三维重建测量法使得膝外翻角的术前个体化测量更加精确。研究方法利用64 名患者的CT 血管造影(CTA)的DICOM数据获取共128 件股骨三维重建模型。 在重建的股骨模型上分别定位髁间凹最高点(点A)、 膝关节线上20 cm 截面的髓腔中点(点B)和股骨头旋转中心(点C)。 之后膝关节外翻角即由股骨远端解剖轴(线AB)与股骨机械轴(线AC)所围成(上述定位过程详见图5)。 经统计分析后, 128 件股骨的平均外翻角值为6.20°±1.20°。 统计分析还发现, 膝外翻角与个体年龄呈显著性正相关, 同一个体的左右侧外翻角呈显著性正相关。重要结论在对北方成年人群进行膝关节置换术时, 选取外翻角为6°可会在重建人体下肢力线上获得更好的术后效果。 在对年长患者进行手术时应选用更大的外翻角。