Study of circular cross correlation and phase lag to estimate knee angle: an application to prosthesis

This paper present an application of cross correlation coefficient (CCC) to predict knee angle and propose a novel method to design unilateral transfemoral prosthesis. The phase lag at which peak CCC occurs is used to predict knee angle. Sixteen healthy subjects were required to walk in movement analysis lab. Circular cross correlation was preferred as the knee angle time series is periodic while walking. An error profile was generated to assess the suitability of this technique. One sampled t-test shows the mean error of 4.9° to 7.9° with 95% confidence interval. Thus, phase lag algorithm has the potential to be implemented in hardware to design adaptive unilateral transfemoral prosthesis.