Effect of recording angle on accuracy of Kinovea-based kinematic gait analysis compared to three-dimensional motion analysis in healthy dogs: optimal at 90° recording angle

The goal of this study was to investigate the effect of recording angle on the accuracy of 2-D Kinovea-based kinematic motion analysis (KMA) compared to 3-D KMA in dogs. In this prospective study, 3-D marker-based KMA (VICON-Nexus, version 2.12.1, and Procalc, version 1.6; VICON Motion Systems Ltd) was performed on healthy dogs (body weight ≥ 20 kg) walking on a treadmill (study period: November 2022). Simultaneously, dogs were video-recorded by 3 smartphones (iPhone SE; Apple Inc) at 1.50 m distance and 45°, 90°, and 135° recording angles relative to the shoulder for Kinovea-based, angle-calibrated KMA. Shoulder, elbow, carpal, hip, stifle, and tarsal joint kinematics were calculated for 3 synchronized gait cycles. Each gait cycle was divided into 10 increments. The estimated difference between 3-D KMA and Kinovea was assessed using robust linear mixed-effects models. 34 dogs were included. Differences of less than 5° between methods were considered reasonable. At a 45° recording angle, the estimated joint angle difference was < 5° for the carpus and hip during ≥ 5 of 10 gait cycle increments. At 90°, the difference was < 5° across all joints for ≥ 9 of 10 increments and at 135° was < 5° for the elbow, carpus, and hip for ≥ 7 of 10 increments. Kinovea-based kinematics were most accurate when recorded at 90°. At 45°, Kinovea provided accurate data for the carpus and hip and at 135° for the elbow, carpus, and hip. While angle-calibrated kinematic measurements can be accurate when using Kinovea for canine KMA, a 90° recording angle is preferable.