Validation of non-radiographic APECS software in comparison with standard radiographic measurement of full-length lower limb hip-knee-ankle angle in elderly obese women

Introduction
Evidence suggests that obesity and ageing in women are linked to angular knee abnormalities. The hip-knee-ankle (HKA) angle on a full-limb radiograph is the gold standard measure of lower limb alignment. The AI Posture Evaluation and Correction System (APECS) software is a non-radiographic mobile application designed for whole-body posture assessment. Since exposure to X-ray is associated with harmful effects, there is a need to find a safe and valid alternative for measuring HKA angle. The objective of this research was to determine the validity of the non-radiographic APECS software in comparison with standard radiographic measurement of HKA angle.

Methods
The present cross-sectional diagnostic accuracy study was conducted in a tertiary care hospital of Belagavi, Karnataka, India. Overall, 45 elderly obese females aged 60–80 years with a body mass index of 25 were included. HKA angle was marked bilaterally. Full-limb radiographs were taken and angles were marked with 2.0 version software, DXM model. For the APECS software, full-limb photographs were taken with landmarks indicated with radiant markers and angles were autogenerated by the software.

Results
The Pearson correlation coefficient between the APECS application and the gold standard (X-ray) was 0.9874 (98.74% of matching). The agreement between standard radiograph and the average of all examiners’ APECS Pro measurements (including right and left sides) equalled 94.64% (kappa = 0.8323; p = 0.001), which suggests very good agreement.

Conclusions
The APECS application demonstrated a high percentage of matching (98.74%) and agreement (94.64%), indicating its excellent validity in measuring HKA angle.