Accuracy and reliability of a smartphone application for measuring the knee joint angle

Abstract

Recently, a photo-based smartphone application for angle measurement-"Grid line imaging application Professional"-was developed to evaluate joint disease treatments. The aim of this study was to determine the accuracy and reliability of the application. [Participants and Methods] We measured the knee joint of a mannequin using an application and a universal goniometer. Twelve examiners measured eight knee joints of mannequins at different arbitrary angles using the application and a universal goniometer. Correlations between the application and universal goniometer measurements were examined using scatter plots and correlation coefficients. Systematic errors of the application were visually confirmed using the Bland-Altman method. Intra-class correlation coefficients were used to evaluate the inter-examiner reliability of the application. [Results] The application and universal goniometer measurements showed a good correlation (r=0.99) and no systematic error. The intra-class correlation coefficient for inter-examiner reliability was 0.999. Furthermore, to evaluate intra-examiner reliability, six examiners measured six different knee joints twice using the application on a 2-day interval. The intra-class correlation coefficient for intra-examiner reliability was 0.982. [Conclusion] The accuracy of the application was equivalent to that of a universal goniometer, and both the inter-and intra-examiner reliabilities of the application were almost perfect.

Video-based Goniometer Applications for Measuring Knee Joint Angles during Walking in Neurological Patients: A Validity, Reliability and Usability Study

“…Some apps require that the smartphone is fixed over the subjects’ skin to collect measures of joint angles using the built-in accelerometer, gyroscope, and magnetometer signals [ 14 , 16 , 17 ]. Other apps do not require that the smartphone is in direct contact with the subject’s skin because joint angles are drawn on digital photography [ 14 , 18 , 19 ]. Specifically, the latter app type offers additional benefits to accelerometer-based goniometric apps.…”

Development of a Stretchable Conductive Sensor for Flexible Deformation: A Preliminary Study

“…However, it requires a radiological imaging system, time, cost, and even radiation exposure for the patient [4]. Innovations in measurement are also evolving and recent, there are researchers who develop mobile applications to take photo-based knee joint angle ROM readings [5] and some even propose a simplified inertial sensor method [6]. Although these innovative methods can provide more sensitive digital readings, the accuracy in taking repeat readings is low because the same level and position setting is required when taking readings at the next assessment.…”