Measurement of rotational deformity: using a smartphone application is more accurate than conventional methods

We assessed the accuracy of three different methods measuring the angle between two fixed Kirschner wires for the potential purpose of determining correction during rotational osteotomy of long bones.

Thirty-one orthopaedic consultants and registrars were prospectively asked to measure the angle between two fixed Kirschner wires in four saw bones models using three different techniques: visual estimation (VE), osteotomy templates (OT), and a contemporary smartphone (iPhone4; SP) with its gyroscopic function. These three methods were compared with the value obtained by computed tomography (CTV), which we considered the preferred value.

For the pooled data for all four bone models, the mean difference of the VE compared with the CTV was 5.4° ± 5.3°; the mean difference of the OT compared with the CTV was 2.9 ± 3.8°; and the mean difference of the SP compared with the CTV was 0.8 ± 0.9°. Using the pooled data, the difference between using each of these methods was highly significant, as demonstrated by the one-way analysis of variance across groups (P ≤ 0.001). In addition, for the pooled data the independent t-test between each pair of the three methods (VE and OT, VE and SP, and OT and SP) also demonstrated these differences were highly significant (P ≤ 0.001) for all three comparisons. In this study, the number of years of orthopaedic experience did not significantly influence the ability of individual test subjects.

Measurement of a rotational deformity using a SP app was significantly more accurate and consistent than both VE and OT. We believe the currently available SP technology provides orthopaedic surgeons with a significantly better alternative method of determining the magnitude of rotational deformity when performing corrective osteotomies.