THE EFFECT OF FOOT STRUCTURE ON THE 3-DIMENSIONAL KINEMATIC COUPLING BEHAVIOR OF THE LEG AND REAR FOOT

Background and Purpose. Differences in foot structures have been repor ted to account for the large variability in findings in previous studi es that have examined the relationship between foot structure and the interdependent rotations of the lower extremity. The purpose of this s tudy was to determine, in individuals with radiographically distinct f oot structures, the effect of foot structure on three-dimensional kine matic behavior of the leg and rear foot during running. Subjects and M ethods. Based on radiographic measurements, 10 recreational runners we re assigned to a low rear-foot group and another 10 recreational runne rs were assigned to a high rear-fool group. Three-dimensional kinemati c data were collected during treadmill running. Individual axis rotati ons and the ''coupled'' relationship betwen the leg and rear-foot segm ents were defined using a Cardan angle system of three ordered rotatio ns. Results. The predominant rotations suggest a combined subtalar and talocalcaneal joint axis to favor calcaneal eversion and inversion fo r the low rear-foot group and tibial medial and lateral rotation for t he high rear-foot group. Group differences were also found for the cou pling 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 t o each foot group may enhance our understanding of lower-extremity inj uries related to certain foot structures. An assessment of the couplin g relationship in combination with traditional frontal-plane measureme nts may better guide decisions regarding selection of footwear and ort hoses.