## 2 Materials and Methods
### Participants  
Nineteen individuals with knee OA (17 females and 2 males) who met the inclusion criteria were enrolled in the study. A given control participant was recruited to match a corresponding knee OA participant, based on the same gender, age (\(\pm 3\) years). The study was approved by the university's Institutional Review Board and written informed consent was obtained from all participants. Nineteen participants in each group were calculated via an a priori power analysis to provide 97.5% power with an effect size of 1.33 at \(\alpha=0.05\) to detect differences. The data used for the estimates were the result of comprehensive equilibrium scores reported in a study that was conducted by [PERSON] and colleagues on postural control of individuals with fibromyalgiaalgia [36].  
All participants in both groups were free of the following: (1) concurrent medical conditions that could impair balance, such as neurological or significant musculoskeletal disease, inner ear disease, or permanent lower-limb injury; (2) inability to walk without assistance; and (3) an abnormal optometric or ophthalmic examination within the preceding six months. The diagnosis of knee OA was made based on a mild to moderate diagnosis of knee OA in one knee. The following conditions were excluded from this study: asymptomatic osteoarthritis of one or both knees, inflammatory arthritis, major lower extremity joint surgery (e.g., knee arthrotomy within the previous six months), any condition that significantly limits local ambulation (e.g., amputation or stroke), use of gait aids for ambulation, and dementia or inability to understand and follow directions.  
On the basis of gender, age, height, weight and BMI, participants with knee OA were matched to asymptomatic control participants (healthy knee group). Control participants with rheumatoid or any other type of arthritis, a history of lower extremity injury, or prolonged knee pain requiring medication or knee surgery were excluded from the control group. Additionally, control participants with recurrent or prolonged knee pain within the previous month were excluded, even if they were pain-free on the day of testing. Participant characteristics are presented in Table 1. Demographic variables assessed for this study included (a) age, (b) height, (c) mass and (d) body mass index (BMI). These data results were analyzed using independent t-test to evaluate differences among variables and there were no statistically significant differences between knee OA group and healthy knee group in demographics.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Participant** & **Knee OA** & **Healthy Knee** & **t** & **df** & \(p\) \\
**Characteristics** & **Mean (S.D.)** & **Mean (S.D.)** & & & \\ \hline Age (yr) & 52.53 (\(\pm 10.80\)) & 51.32 (\(\pm 10.26\)) & \(-0.354\) & 36 & 0.725 \\ Height (cm) & 163.90 (\(\pm 10.30\)) & 164.43 (\(\pm 8.33\)) & 0.179 & 36 & 0.859 \\ Mass (kg) & 77.05 (\(\pm 12.78\)) & 75.26 (\(\pm 13.02\)) & \(-0.427\) & 36 & 0.672 \\ BMI (kg/m\({}^{2}\)) & 28.83 (\(\pm 5.04\)) & 27.81 (\(\pm 4.29\)) & \(-0.669\) & 36 & 0.508 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Participant demographics.