Background/Purpose: Postural stability is an indicator of static standing balance and a critical component of physical function and fall prevention among those with knee OA. Examining associations between postural stability and physical or functional health outcomes can inform the better monitoring of disease progression and design of ideal treatments. There is limited research on the association between postural stability and outcomes of physical health and functional status in knee OA. The purpose of this study was to investigate the relationships between postural stability and pain, stiffness, physical function, walking ability, and muscle strength and power in a large population of adults with symptomatic knee OA.

Methods: We performed a cross-sectional analysis of baseline data collected as part of a randomized trial comparing Tai Chi with physical therapy. Participants who met the ACR criteria for symptomatic knee OA completed the WOMAC and a battery of physical performance tests (Berg Balance, 6 Minute Walk, 20 Meter Walk, muscle strength and power) at baseline (Table). Postural stability was quantified using a standardized balance force plate to measure center of pressure (COP) excursions in Anterior–Posterior (A-P) and Medial-Lateral Direction (M-L), with eyes open and closed. Greater excursion amplitude indicates greater postural instability.

Results: There were 173 participants (mean age: 60 years, BMI: 33, 69% female, 55% white, and 93% Kellgren/Lawrence Grade ≥ 2). Greater COP excursion amplitude, with eyes open or closed and in the A-P or M-L direction, was associated with higher pain (r=0.15-0.16, P<=0.05) and stiffness (r=0.24-0.25, P<=0.002). Greater COP excursion amplitude in the M-L direction (eyes open or closed) or A-P direction (eyes open) was also significantly associated with lower peak power at low (r=-0.15- -0.17, P<=0.05) or high resistance (r=-0.16- -0.19, P<=0.04). COP excursion variables were not significantly associated with BMI, WOMAC function, dynamic balance (Berg balance), muscle strength, or the walk tests (Table).

Conclusion: Participants with symptomatic knee OA who had greater postural stability tended to have less pain, less stiffness, and more muscle power. Our findings indicate that therapeutic interventions that positively modulate postural stability may reduce pain and stiffness among those with knee OA. In addition, static postural stability may be an informative performance metric to assist researchers and clinicians to better monitor symptoms, design novel treatment, or prevent future falls.