Estimation of the knee joint location using colour video

Abstract Analysis of the knee joint moment might be useful for predicting the risk of prosthetic loosening. The moment can be estimated if the location of the centre of pressure in the knee joint and the ground reaction force vector are known. Usually, skin mounted markers are used to locate the knee joint centre. Since marker based methods have several drawbacks investigations of alternative methods are needed. A new method for location of the knee joint is outlined in this paper. The subject is video filmed during gait with an elastic blue band wrapped around the knee. The band is located by splitting the video images into the RGB-components, and the centroid of the band is used as an estimate of the knee joint centre location. The band is easier to mount than markers, and it is not sensitive for axial leg rotation like markers are, which simplifies the analysis. If desired, the axial leg rotation can be determined by attaching a circular cyan marker on the band. The centroid of the marker relative to the band centroid gives an approximation of the leg rotation. In this study, the band could easily be located in the images and the leg axial rotation estimated in the frontal and the sagittal view showed the same trend. Further, the band-based results were found to be comparable to results where a marker was used to locate the knee joint centre.