# Validation of the Posture Analyzing and Virtual Reconstruction (PAViR) System for Measuring the Hip–Knee–Ankle Angle Using 2D Photogrammetry and Computer Vision

## TL;DR

This study validates a new non-invasive system for measuring lower limb angles using 2D photogrammetry and computer vision.

## Contribution

The PAViR system is validated as a reliable alternative to existing tools for measuring the Hip–Knee–Ankle angle.

## Key findings

- PAViR showed perfect correlation (r = 0.999) with Kinovea for HKA angle measurements.
- Bland–Altman analysis confirmed clinically acceptable agreement within ±2°.
- The system demonstrated minimal systematic bias and narrow limits of agreement.

## Abstract

Background. Accurate assessment of lower limb alignment is critical in diagnostic decision-making for musculoskeletal disorders. This study aimed to validate the PAViR (Posture Analyzing and Virtual Reconstruction) system, a non-invasive device based on artificial vision and 2D photogrammetry, for measuring the Hip–Knee–Ankle (HKA) angle. Method. A total of sixty-one adult participants were evaluated using the PAViR system, and the results were compared against Kinovea, a validated open-source software commonly used for 2D kinematic and angular analysis in clinical and sports biomechanics. Statistical analyses included the Shapiro–Wilk test, Pearson correlation, and Bland–Altman plots. Results. The correlation between both systems was perfect (r = 0.999; p < 0.001). The Bland–Altman analysis showed differences of 0.03° (left) and 0.04° (right), with limits of agreement between −0.25° and +0.75°, within the clinically acceptable margin of ±2°. These findings demonstrate that the PAViR system shows excellent agreement with a validated 2D photogrammetry reference method for measuring the Hip-Knee-Ankle angle in asymptomatic adults. The narrow limits of agreement (−0.25° to +0.75°) and minimal systematic bias (0.03–0.04°) support the technical validity of PAViR for static coronal plane alignment assessment under controlled conditions. Conclusions. Further validation studies in clinical populations and dynamic contexts are necessary to establish broader applicability and clinical utility. Its integration could enhance lower limb assessment in orthopedic, sports, and preventive care. Further validation studies in clinical populations with musculoskeletal pathology, dynamic functional contexts, and direct comparison with radiographic gold standards are necessary to establish broader applicability and clinical utility.