# Measurement of Lower Extremity Alignment Using a Smartphone Application
## 4 Discussion
In comparison, the smartphone application calculated the lower extremity alignment angle using the ratio between the knee and ankle joints by specifying the inflection points, which are the thinnest parts of the inner and outer skin on the right and left knee and ankle joints. Therefore, measurement of the lower extremity alignment angle using the application was easier, facilitating self-diagnosis. To evaluate whether the smartphone application can be used as a diagnostic aid in clinical medicine, the correlation between the actual lower extremity alignment angle and the PLEAA in the application was analyzed, and values of 0.608 to 0.627 (\(p<0.01\)) were obtained. This was interpreted as an intermediate positive correlation according to [PERSON]'s correlation guidelines [25]. In a similar study that used photography to measure lower extremity alignment, [PERSON]'s correlation coefficient between the actual lower extremity alignment angle and the lower extremity alignment angle measured using photographs was 0.92 (\(p<0.001\)), which indicated a strong correlation [17]. In another study, [PERSON]'s correlation coefficient for the actual lower extremity alignment angle and the lower extremity alignment angle measured using the body surface topography was \(-0.702\) (\(p<0.001\)), which indicated a strong negative correlation [18]. With the exception of radiography, the results of the present and previous studies on measurement of lower extremity alignment suggest that there are other diagnostics modalities in clinical medicine that do not involve radiation exposure. Photography and body surface topography generally require specialized equipment or programs for self-diagnosis, as well as specialized expertise. According to a previous study in which body surface topography was used to measure lower extremity alignment by attaching a marker to a specific anatomical location on the patella, it would be difficult to measure severe valgus knee using body surface topography because the lateral traction of the patella in these patients is strong and can increase its instability, and the resulting dislocation would lead to changes in location, which is thought to greatly change the actual lower extremity alignment angle [27]. Therefore, it is difficult for the general public to use these methods to prevent and manage lower extremity alignment problems through self-diagnosis. In this regard, an application that can serve as a tool for measuring lower extremity alignment may be helpful. This study had some limitations. First, although the two evaluators were fully familiar with the use of measurement tools, the measurements can be affected depending on the user's proficiency because the points in the application were required to be adjusted using a finger or touch pen. Second, the effects of the participants age and K-L grade and pelvis oblique on the results was not investigated. In addition, measurements were performed in posture identical (as much as possible) to that used during the radiographic imaging; however, other postures such as comfortable posture and legs gathered were not measured, and the agreement of the measured lower extremity alignment angle was not confirmed. Further, the location of the smartphone camera was also not considered. Thirdly, the actual lower extremity alignment angle and the PLEAA measured using the application differed. The correlation between the two values was also insufficient at an intermediate level. In this respect, additional studies with a larger number of participants are needed to increase the accuracy and correlation of lower extremity alignment measured using the smartphone application. In addition, it is necessary to improve the smartphone application so that the lower extremity alignment angle can be measured even in comfortable position and various camara location. Further, it is important to automatically detect the measurement point to avoid the results being affected by the user.