Postural Instability During Single Limb Stance For Individuals With Previous Ankle Injury

Abstract

Up to 74% of people who sprain their ankle develop chronic ankle instability (CAI). Despite a history of lateral ankle trauma, some people can remain active without recurrent injury or loss of function (copers). Understanding the differences between copers and CAI patients may elucidate the mechanism present in copers but absent in CAI patients. PURPOSE: To investigate postural instability during single limb stance in CAI, Copers and Controls. METHODS: Twenty four CAI (age 21.7 ± 2.8 yrs), 24 Copers (age 20.8 ± 1.5 yrs), and 24 Controls (age 21.8 ± 2.6yrs) completed four, single limb, quiet stance trials (2 trials per limb, 30 seconds each). Copers and CAI patients had at least one previous moderate ankle sprain but copers resumed all pre-injury activity without limitation or recurrent injury while CAI patients had recurrent sprains and giving way episodes. Ground reaction forces (GRF), collected at 100HZ, were used to calculate the Center of Pressure (COP) location. GRF accelerations were doubly integrated to obtain estimates of the Center of Mass (COM) location. The distances between the COP and COM in the transverse plane (COP-COM moment arm) were then calculated to identify the peak moment arms in the mediolateral (Xmax), anteroposterior (Ymax) and resultant (Rmax) directions as well as the mean resultant moment arm (Rmean) for each trial. Limb averages were then submitted for statistical analysis. RESULTS: Separate two-way ANOVAs (Limb x Group) indicated significant group main effects for Xmax, Ymax, and Rmean. Post hoc analyses revealed that CAI had larger Xmax (1.21±0.25 cm) and Ymax (1.16±0.21 cm) peak moment arms when compared to controls (Xmax: 1.07±0.18 cm, Ymax: 1.01±0.16 cm) (both p<0.02) but copers (Xmax: 1.11±0.22 cm, Ymax: 1.08±0.19 cm) and controls did not differ for Xmax or Ymax. Both CAI and Copers had larger Rmean (CAI: 0.35±0.06 cm, Copers: 0.33±0.06 cm) values when compared to controls (0.30±0.04 cm) (p<0.01) but did not differ from each other. CONCLUSION: The Rmean results indicate that individuals with previous ankle injury (CAI and Copers) have increased postural instability during single limb stance. However, CAI patients' inability to limit peak separations of the COP-COM moment arm may represent the mechanism absent in CAI patients. Supported by the University of Florida, CHHP Opportunity Fund.