Failure to correct femoral anteversion on the AP Pelvis radiograph leads to errors in prosthesis selection in total hip arthroplasty

Abstract

AbstractThe antero‐posterior pelvis radiograph is used in templating to calculate the size of components used in hip arthroplasty. This study investigates whether failure to account for femoral neck anteversion, when obtaining preoperative AP radiographs, may lead to the selection of an incorrectly sized femoral stem. Three anatomically correct saw‐bone models were labelled with radio‐opaque markers. Serial radiographs were taken as each model was rotated though successive angles, as determined with a goniometer. The resultant offset was measured from each image. The length of offset is greatest at 15° degrees of internal rotation. The length of offset is altered by rotation (Friedman Xr2 9.0, k 4, N 3, P <0.01, two‐tailed test). The results indicate that, for the Exeter hip system, this could lead to the selection of a stem two sizes too small. Lesser degrees of rotation, not readily identified by looking at the image, could still lead to the selection of an incorrectly sized stem. This finding is applicable to other modular hip replacement systems in common use. To ensure that patients receive hip prostheses of correct size, preoperative radiographs should account properly for femoral anteversion. A foot box may help to standardise the amount of femoral anteversion when preoperative radiographs are taken.