Temporal Activation of Core Muscles and Vasti in Isolated Patellofemoral Osteoarthritis

Investigators collected the EMG activity of VMO, VL, GM, multifidus, and TrA using bipolar Ag-AgCl disposable surface electrodes (Better signal solution medical supply Co., limited, Zhongshan, China) and eight channels high-resolution wireless bio amplifier (WBA) system (Biomation, Almonte, Canada). Electromyographic data were sampled at 1000 Hz and bandpass filtered at 50-200 Hz.

For each muscle, three electrodes were used; two electrodes were placed ~ 30 mm apart in the direction of the muscle fibers and a ground electrode was placed over the closest bony prominence. Before placement of the electrodes, the subject's skin was cleaned with alcohol to reduce impedance and excess hair was removed to eliminate shifting of the electrodes if needed.

The stair-stepping task consisted of ascending 2 steps (each step was 40 cm in width, 20 cm in height, without handrails. The depth of the first and second steps was 30 cm and 40 cm, respectively) . Participants were asked to stand on the floor confronting the stairs and 20 cm away from the edge of the initial step. The stair ascent task was performed barefooted while arms hanged at the side of the body. Patients started ascending the steps immediately in response to a command, at their normal speed with their affected limb. Investigators didn't control the speed of stair ascent, because controlling the timing of stair-stepping can alter the electromyographic signal as shown earlier for gait in asymptomatic subjects. Healthy subjects started ascending stairs with their dominant limb .

Before data acquisition, participants performed one practice trial of stair ascent to get familiarized with the task. Then the participants performed three test trials with thirty seconds of rest after each trial to prevent fatigue. The raw data were stored on a personal computer for analysis with a custom program in Matlab (Math Works, Natick, Massachusetts, USA). Investigators used a mean of data in three trials for analysis.

Statistical Analysis:

Data management and analysis were conducted using the statistical package for social studies (SPSS) version 22 for windows (IBM SPSS, Chicago, IL, USA). Normal distribution of the data was tested using the Shapiro-Wilk test. The homogeneity of variances between groups was examined using Levene's test. Descriptive data are expressed as mean ± standard deviation. An independent t-test was conducted for comparison of subject characteristics; age, body mass index (BMI), weight and height, between both groups. A univariate test of one way MANOVA was performed to compare EMG onset of each muscle between both groups. Post-hoc analysis using the Bonferroni method was carried out for subsequent multiple comparison. The level of significance for all statistical tests was set at p < 0.05.