Reliability and validity of OpenPose for measuring HKA angle in dynamic walking videos in patients with knee osteoarthritis.

The hip-knee-ankle (HKA) angle is essential to assess surgical evaluation and disease progression in patients with knee osteoarthritis (KOA). Rapid, radiation-free assessment methods are a key area of research. This study investigates the reliability and validity of OpenPose, video-based human pose estimation method, for determining the HKA angle in KOA patients. In this study, we analyzed 50 knees affected by osteoarthritis. The HKA angle was measured using the pose estimation method and X-ray imaging before total knee arthroplasty. The pose estimation method demonstrated excellent test-retest reliability (ICC 1,1 = 1.000) and good consistency with radiography (ICC 2,1 = 0.897), with linear regression analysis showing a good correlation (R2 = 0.814). Compared with radiography, the pose estimation method exhibited a fixed error of 0.131°. This is the first study to examine the feasibility of measuring the HKA angle from frontal-view videos of patients walking normally by using the pose estimation method. Using the pose estimation method to measure the HKA angle in knee osteoarthritis patients is reliable and valid. The pose estimation method provides a safe, cost-effective, and user-friendly solution for monitoring lower limb alignment, with promising applications in remote healthcare and rehabilitation management. It eliminates radiation exposure, avoiding the health risks associated with X-ray imaging, and it does not require specialized medical equipment, enabling fully automated analysis.