FRI0580-HPR Biomechanical and neuromuscular characteristics of the one leg stand test in patients with knee osteoarthritis and self-reported knee instability
Authors: D. C. Sanchez-Ramirez, B. Malfait, F. Luyten, M. van der Leeden, J. van Dieën, W. Lems, J. Dekker, S. Verschueren
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> Patients with knee osteoarthritis (OA) often have decreased knee instability which usually translates into activity limitations. Further understanding of the biomechanical and neuromuscular characteristics associated with self-reported knee instability are needed to better assess and treat this problem in this group of patients. <h3>Objectives</h3> The aim of this study was to investigate the knee joint kinematics, kinetics and muscle activation patterns during one leg stace in patients with knee osteoarthritis (OA), and to assess their associations with self-reported knee instability. <h3>Methods</h3> 25 females with knee OA (mean age of 69.7 years and BMI 27.8) were included in the study. In the One-Leg Stand Test (OLST) the patients were asked to stand on one leg for 30s. The time that the patients could stand in one leg was recorded. The test was performed three times, the average time was used for the analyses. 3D motion analysis (Vicon) combined with surface electromyography (Zerowire, Aurion) was used to capture the movements. Knee joint kinematics, kinetics and mean muscle activities (Root Mean Square), as well as center of mass (COM) displacement on the three axes were analyzed during the OLST. Self-reported knee instability (episodes of buckling, shifting or giving way) was present in 5 patients (20%). T-test and Pearson’s correlations coefficients were used to assess the relationships. <h3>Results</h3> There were no significant differences in mean knee joint kinematics, kinetics, muscle activation patterns or COM displacement during the average time of the OLST complexion between patients with and without self-reported knee instability. The average time of the OLST was positively correlated with medial hamstring (MH) activity (r=0.40, p=0.04) in the whole group of patients with knee OA, as well as in the subgroup of patients without self-reported knee instability (r=0.46, p=0.04). Knee extension moment was highly correlated with larger OLST time (r=0.92, p=0.02) in patients whom reported knee instability during the past three months. <h3>Conclusions</h3> In the whole group of patients with knee OA and in the subgroup of “stable” patients, better performance of the one leg stand test was correlated with greater MH activity which might suggest an attempt to compensate greater medial knee laxity, usually present in this group of patients. On the other hand, longer time standing in one leg was correlated with higher knee extension moment in self-reported instable patients causing what the patients defined as an intentional “blockage” of the knee in extension. It seems that there are different strategies used for patients with and without self-reported knee instability in an attempt to keep the knee in a stable position during a challenging weight bearing task, which result in better postural control. These preliminary results might be useful to better understand the mechanisms influencing knee instability and their consequences in patients with knee OA. However, further research in a larger sample population is needed to confirm our findings and to clarify their implications for therapy. <h3>Disclosure of Interest</h3> None Declared