X線軸位像での臼蓋コンポーネント前方開角の新しい計測法

New Method of Measuring the Acetabular Anteversion Angle on Lateral Radiographs Following Total Hip Arthroplasty

　X線軸位像は，人工股関節全置換術(THA)における臼蓋コンポーネント前方開角の測定方法として簡便に施行可能であるが，骨盤傾斜の影響などによる再現性の低さが指摘されている．THA受療者において，大・小坐骨切痕の接線を坐骨軸，坐骨軸と前骨盤平面とのなす角を坐骨軸傾斜角と定義し，これを3次元CT骨盤矢状断像を用いて計測した．坐骨軸は前骨盤平面に対して前傾しており，坐骨軸傾斜角は18.0±3.5°であった．X線軸位像において坐骨軸と坐骨軸傾斜角を指標とし，骨盤傾斜に影響されにくく再現性の高い前方開角の測定が可能と考える．

　Although lateral radiographs are useful for evaluating acetabular anteversion following total hip arthroplasty (THA), they are affected by variations in pelvic position and radiographic technique.　In this study we obtained preoperative three-dimensional computed tomography (3D-CT) images of the 122 hips of 122 patients scheduled for THA.　We defined the ischial axis (IA) as a line drawn between the lessor sciatic notch and greater sciatic notch, and the ischial axis angle (IAA) as the angle formed by the IA and anterior pelvic plane.　We measured the IAA on 3D-CT images.　The IA was tilted anteriorly in all of the patients, and the mean IAA was 18.0±3.5 degrees.　The findings in this study will be useful for measuring acetabular anteversion on lateral radiographs in patients who have undergone THA.