On the Measurement of Dynamic Stability of Normal and Osteoarthritic Human Knee During Ascending and Descending the Stairs

The aim of this study is to measure the variation of the flexion-extension angles of the knee and to study the stability of the knees movements during ascending and descending the stairs for healthy subjects and for patients suffering of osteoarthritic knee (OAK). Tools of nonlinear dynamics are used in order to quantify the stability of human healthy knee and OAK joints during ascending and descending the stairs. The values of Lyapunov exponents (LE), which represent the measure of instability of knee movements, are computed based on the experimental time series collected for both knee joints movements: flexion-extension (fl-ext) in sagittal plane and varus-valgus rotation (var-valg) in frontal plane. LEs obtained for the OAK are associated with more divergence, more variability and less stability, being larger than those are obtained for the knees of healthy subjects.