The effect of foot structure on the three-dimensional kinematic coupling behavior of the leg and rear foot.

ABSTRACT

BACKGROUND AND PURPOSE: Differences in foot structures have been reported to account for the large variability in findings in previous studies that have examined the relationship between foot structure and the interdependent rotations of the lower extremity. The purpose of this study was to determine, in individuals with radiographically distinct foot structures, the effect of foot structure on three-dimensional kinematic behavior of the leg and rear foot during running. SUBJECTS AND METHODS: Based on radiographic measurements, 10 recreational runners were assigned to a low rear-foot group and another 10 recreational runners were assigned to a high rear-foot group. Three-dimensional kinematic data were collected during treadmill running. Individual axis rotations and the "coupled" relationship between the leg and rear-foot segments were defined using a Cardan angle system of three ordered rotations. RESULTS: The predominant rotations suggest a combined subtalar and talocalcaneal joint axis to favor calcaneal eversion and inversion for the low rear-foot group and tibial medial and lateral rotation for the high rear-foot group. Group differences were also found for the coupling ratio, which described the proportion of calcaneal eversion and inversion transferred or coupled to tibial axial rotation. CONCLUSION AND DISCUSSION: The rotational patterns and coupling response unique to each foot group may enhance our understanding of lower-extremity injuries related to certain foot structures. An assessment of the coupling relationship in combination with traditional frontal-plane measurements may better guide decisions regarding selection of footwear and orthoses.