Abstract
Functional instability (FI) is a term used to describe the condition of recurrent sprains and/or the feeling of giving way. It is believed that impaired proprioception and decreased postural stability accompany the FI ankle. However, recent studies reported that postural control is not affected by ankles with FI. For comprehensive understanding, this study evaluated the difference between FI and normal healthy ankles in proprioception and static postural control. Sixteen male subjects were recruited: eight had unilateral FI ankles and eight had non-injured ankles. The Biodex III isokinetic dynamometer was used to asses active and passive ankle repositioning sense. Static balance ability was assessed by Kistler force plates as mean radius of center of pressure (COP) distribution. Pearson's correlation, independent t test and one-way ANOVA were used to evaluate the difference between groups. We found the following: (1) strong correlations between active ankle repositioning sense and static balance abilities; (2) FI ankles have large passive ankle repositioning sense and mean radius of COP compared to healthy ankles; (3) significant correlations between active ankle repositioning sense and static balance control for healthy ankles. We conclude that FI ankles have impaired passive repositioning sense and poor static balance control compared to normal ankles. More research is needed to examine the effects of exercise training or rehabilitation programs on passive ankle repositioning sense.