Evaluation of the smartphone for measurement of femoral rotational deformity

Abstract

A novel measurement technique has been designed to assess femoral rotation deformation. The purpose of this study was to evaluate smartphone-aided measurement, including measurement software, intra-observer differences and the occurrence frequency of the unacceptable outliers. Five positions (intact bone, external and internal rotations of 20° and 40° of the distal blocks after dividing the femoral shafts using a saw) were used in each of the five artificial femora. Guide wires were separately inserted into the proximal and distal ends of the model femora with a navigation system and the intersection angles between the guide wires were measured with a smartphone. The values obtained by two measurement software packages (Smart Tools and Super Swiss Army Knife) were compared with that measured on the overlapped computed tomography images. There were no significant differences between the intersection angles measured by smartphone and that measured on the overlapped images (P = 0.24). The mean absolute difference between pairs of measurements of the two software packages for all guide wire angles was 2.33 ± 2.34°, without statistically significant difference (P = 0.33). There was a significant correlation (r = 0.99) between the first and second (1 week apart) measurements with the same measurement tool. The values of offset capability index of the Smart Tools and the Super Swiss Army Knife measurement tools were 1.62 and 1.13, respectively. Smartphone-aided measurement technique could reliably assess femoral rotation deformation with more accurate angle measurement for software with zero calibration function.