# Measurement of Lower Extremity Alignment Using a Smartphone Application
## 4 Discussion  
In this study, we developed and validated a new tool for measuring the lower extremity alignment angle. This tool is an angular deformity-leg diagnosis program on a smartphone. To determine whether the tool can be used in clinical medicine, the actual lower extremity alignment angle measured using radiographs, intratrater reliability, and interrater reliability were compared. In addition, to evaluate whether the tool can be used as a diagnostic aid, correlation analysis was performed for the HKAA and PLEAA measured by the application. The intratarater reliability was judged to be high at 0.968 to 0.995 when the two evaluators repeatedly measured the lower extremity alignment angle using radiographic images and the smartphone application. Our results are consistent with previous reports where the intratarater reliability for the lower extremity alignment angle measured using PACS and a hardcopy of the radiographs was found to be between 0.93 and 0.99 [22]. The results of this study and our results showed similar results. Additionally, the intratarater reliability of the evaluators for each measurement tool in this study was similar. The interrater reliabilities for the actual lower extremity alignment angle and the lower extremity alignment angle measured using the application ranged from 0.752 to 0.767, which indicated high reliability. Moreover, although the reliability was low when the results of PACS and those obtained using a hard copy of radiographs were compared, the ICC evaluation guidelines still showed excellent reliability. Thus, the actual lower extremity alignment angle and that measured using the application were similar [22; 24; 26]. According to a study comparing  
Figure 4: Scatter plot showing the Pearson’s correlation coefficients between HKAA and PLEAA. A positive correlation was observed for HKAA and PLEAA. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **HKAA (A)** & **HKAA (B)** \\ \hline \multirow{3}{*}{PLEAA (A)} & Correlation & 0.608 ** & 0.618 ** \\  & \(p\)-value & 0.000 & 0.000 \\ \cline{1-1}  & N & 90 & 90 \\ \hline \multirow{3}{*}{PLEAA (B)} & Correlation & 0.601 ** & 0.627 ** \\  & \(p\)-value & 0.000 & 0.000 \\ \cline{1-1}  & N & 90 & 90 \\ \hline \hline \end{tabular}  
* \(p<0.01\). HKAA: hip-knee-ankle angle; PLEAA: predicted lower extremity alignment angle.  
\end{table} 
Table 5: [PERSON]’s correlation coefficients between the lower extremity alignment angle measured on radiographic images and the predicted lower extremity alignment angle measured using the smartphone application. lower extremity alignment measured using a hard copy image and PACS, radiography is a standard test method for evaluating the lower extremity alignment [22]. This test method is expensive and requires radiation exposure, specialized equipment, and hospital visits, thus setting limitations in terms of preventing and managing knee diseases through self-diagnosis in daily life. As such, the smartphone application can be a good alternative as it can evaluate lower extremity alignment using any smartphone possessed by an individual. The interrater reliability of the lower extremity alignment angle measured using radiographs was 0.984, whereas that of the lower extremity alignment angle measured using the application was 0.969. These results indicate high reliability. The results of this study seem to be in accordance with those of previous studies, where the interrater reliability for the lower extremity alignment angle measured using photographs and radiographs was 0.988 [17; 24]. The use of a smartphone camera to measure lower extremity alignment may be an alternative to radiography, thus reducing the risk of radiation exposure. However, this could not be confirmed because of the need for professional knowledge, such as that of the accurate anatomical location [17].