Static and local dynamic stability of subjects with knee joint osteoarthritis

Stability is defined as the ability to control the amplitude and velocity of center of gravity (CoG) changes during quiet standing, and to decrease the risk of falling during walking. Few studies exist which examine the local dynamic stability of those with knee joint osteoarthritis (OA). Nevertheless, it is debatable whether the stability of OA subjects differs from that of normal subjects or not. The aim of this study was to evaluate the static and local dynamic stability of the subjects with knee OA in comparison to normal subjects. Fifteen OA subjects and 15 healthy subjects with matching age, weight, and gender participated in this study. A Qualysis motion analysis system incorporating a Kistler force plate was used to record data during quiet standing and when walking on a treadmill. Static stability was evaluated based on center of pressure (COP) sways excursion, path length and velocity in mediolateral and anteroposterior axes. Local dynamic stability was evaluated by the use of short Lyapunov exponent when subjects walk on treadmill. A two-sample test-test was used for the final analysis (α = 0.05). Mean values of the COP excursion in mediolateral and anteroposterior directions, and the velocity of COP in both mediolateral and anteroposterior directions, differed significantly between healthy and OA subjects (p < 0.05). Local dynamic stability of OA subjects appeared to be reduced compared to healthy subjects, especially when ambulating at higher walking speeds (p-value < 0.05). Study results demonstrated that both static and local dynamic stability decreased in OA subjects. This may be in part due to altered control mechanisms which are required for response to perturbations during standing and walking to ensure stability. As a decrease in local dynamic stability is correlated to an increased risk of falling, it is important that this group should receive appropriate treatment interventions to improve standing and walking stability.