College of Public Health and Human Sciences

BACKGROUND: Foot positioning before heel strike has been attributed to chronic ankle instability injury mechanics, and may play a role in developing and perpetuating chronic ankle instability.

PURPOSE: This study was undertaken to determine if a group of individuals with mechanical instability (MI) or a group with functional instability (FI) of the ankle joint demonstrate less foot-floor clearance and a more inverted and plantar flexed position of the foot during the terminal swing phase of the running and walking cycles when compared with a group of ankle sprain copers who had an injury but no residual instability.

STUDY DESIGN: Controlled laboratory study.

METHODS: Three-dimensional motion analysis was performed on 3 groups (n = 11 male athletes each) differentiated based on ankle injury history and ligamentous laxity during walking and running on a raised platform.

RESULTS: The MI group (14.8° ± 12.0°) demonstrated greater maximum foot external rotation than the FI (3.2° ± 6.0°) and coper groups (2.9° ± 11.0°) (P = .01; η(p) (2) = .25) during running and greater rotation than the coper group during walking (3.3° ± 6.1° vs -4.5° ± 4.1°; P = .03; η(p) (2) = .21). The FI group (6.1° ± 3.2°) had greater plantar flexion at minimum than the MI group (0.1° ± 3.5°) during walking (P = .02; η(p) (2) = .25). Other group differences demonstrated large effect sizes, but not statistical significance, including unstable groups having lower minimum metatarsal height than copers during running.

CONCLUSION: Differences in foot and leg position during terminal swing were observed between MI and FI groups and copers. Greater plantar flexion and lower minimum metatarsal height may increase risk for inadvertent contact and thus episodes of instability.

CLINICAL RELEVANCE: Rehabilitation programs may need to address terminal swing to improve mechanics and avoid potential episodes of giving way at the ankle.