DIFFERENCES IN ARCH INDEX, REARFOOT PLANTAR PRESSURE, AND FOREFOOT DEVIATION FROM CENTER OF FORCE TRAJECTORY IN THOSE WITH CHRONIC ANKLE INSTABILITY, NO HISTORY OF LATERAL ANKLE SPRAIN, AND COPERS.

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2014-05
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The purpose of this study was to investigate differences in arch index, rearfoot plantar pressure, and forefoot deviation from center of force trajectory in those with chronic ankle instability, copers, and no history of lateral ankle sprain. A total of fifty-seven subjects from the local community volunteered for this study. There were 20 subjects in the CAI group (age, 20 ± 3 years; height, 173.61 ± 7.84 cm; mass, 73.91 ± 17.58 kg), 20 subjects in the control group (age, 20 ± 1 years; height, 169.90 ± 9.50 cm; mass, 64.53 ± 14.01 kg), and 17 subjects in the copers group (age, 20 ± 2 years; height, 171.34 ± 7.75 cm; mass, 71.18 ± 13.00 kg). Each subject completed one session of testing in which they walked barefoot across pressure mats at a self-selected speed. The composite footprint of each trial was then divided into rearfoot, midfoot, and forefoot for arch index (foot contact area), medial and lateral rearfoot for medial/lateral rearfoot pressure ratios, and then center of force trajectory deviation from a bisection line in the forefoot. The mean of three trials was used for statistical analysis. Each dependent variable (arch index, medial/lateral rearfoot pressure ratio, and forefoot deviation of center of force trajectory) was analyzed through separate 1-way ANOVA, with 1 between-subject factor (CAI, copers, and control) and a Chi-square Test of Independence. Alpha was set at p < .05. For arch index, a one-way ANOVA yielded no significant differences between the three groups (F2,54 = 0.26, p = 0.77, p2 = 0.01, power = 0.09). A Chi-Square test of independence was calculated comparing the categorical foot types between the three groups, which showed no significant differences (2(4) = 6.59, p = 0.16). For rearfoot medial/lateral pressure ratio, a one-way ANOVA yielded no significant differences between the three groups (F2,54 = 0.69, p = 0.50, p2 = 0.03, power = 0.16). A Chi-Square test of independence was calculated comparing the categories of medial versus lateral rearfoot pressure between the three groups, which showed no significant difference (2(2) = 4.80, p = 0.09). For maximal forefoot deviation from center of force trajectory, a one-way ANOVA yielded no significant differences between the three groups (F2,54 = 1.19, p = 0.31, p2 = 0.04, power = 0.25). A Chi-Square test of independence was calculated comparing the categories of medial versus lateral rearfoot pressure between the three groups, which revealed no significant difference (2(4) = 2.77, p = 0.60). These results of the statistical analysis revealed no significant differences between the three groups in regards to arch index, medial/lateral rearfoot pressure, or forefoot deviation from center of force trajectory. Since these dependent variables may not contribute to the development of chronic ankle instability, other factors such as proprioceptive deficits and neuromuscular differences may play a greater role. Therefore, clinicians should work on improving proprioception and strengthening of the ankle joint rather than focusing on foot type or locations of plantar pressure.
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