Ankle osteoarthritis (OA) compromises ankle joint stability in regards to static balance. Unilateral and bilateral osteoarthritis patients often exhibit different limb-loading patterns during static balance tasks. Symmetrical loading has been posited to improve balance performance. Therefore, the purpose of this study was to quantify balance performance in both ankle osteoarthritis patient groups. Twenty-two unilateral and twenty-one bilateral ankle osteoarthritis patients performed three 10-s quiet standing trials with their feet together. Ground reaction force data were collected from force platforms with one under each foot. Center of pressure excursion in the anteroposterior and mediolateral directions as well as the resultant center of pressure were calculated using custom Matlab software. A 2 × 2 repeated measures ANOVA with Cohen's d were used to analyze the differences between groups (unilateral vs. bilateral) and between limbs (affected vs. unaffected) (α = 0.05). No significant differences were found between limbs or groups in either the anteroposterior or mediolateral direction for any measured variable. Though not statistically different, moderate to large effect sizes were observed for mean resultant distance between unilateral and bilateral (d = 0.096, d: 1.0) as well as anteroposterior excursion (p = 0.077, d: 1.731) and mean velocity (p = 0.084, d: 1.50) between affected and unaffected limbs. These large effect sizes suggested clinically relevant differences may exist, particularly in the anteroposterior direction. These findings may suggest that center of pressure is a better measure of postural strategy while center of mass measures may be more representative of postural steadiness. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2749-2754, 2017.

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