A 2D markerless gait analysis protocol to estimate the sagittal joint kinematics of children with cerebral palsy

The quantitative analysis of human movement provides a deep understanding of the pathophysiological mechanisms underlying locomotion. The traditional marker-based stereo-photogrammetric systems and clinical protocols for motion analysis, although very accurate, have a number of disadvantages that limit their use to large clinical facilities. Among the disadvantages is the use of markers on the body, which can make the patient uneasy, especially children with cerebral palsy. To overcome the limitations of the marker-based stereophotogrammetry and to guarantee accuracy, reproducibility and usability of the measurement, a new markerless protocol is introduced, which, estimates the lower limb sagittal joint kinematics from RGB video images combined with measurements from an infrared depth (D) sensor. The validity of the markerless protocol is demonstrated by comparing the estimates obtained, with those resulting from the application of a common protocol applied to marker-based measurements. The joint kinematics patterns obtained from the ML protocol and the one of reference showed a good agreement after removing the angular offsets with RMSD values between 3.5 and 5 degrees for all joints and R values between 0.8 and 1. The interpretation of the differences found in this study should be treated carefully since they are the results not only of different measurement systems but also of different protocols (2D vs 3D). The proposed protocol for the estimation of the 2D joint kinematics of the lower limbs from RGB-D sensor data is a promising low-cost and simple solution for monitoring children with cerebral palsy.