The relationship of static foot structure to dynamic foot function.

Many theories have been advanced concerning the relationship between structure and function in the human foot, yet few of these theories have been subjected to quantitative examination. In this study, foot structure was characterized by 27 measurements taken from standardized lateral and dorsi-plantar weight-bearing plain radiographs of 50 healthy adult subjects. Regional plantar pressure distribution data collected from the same feet were chosen as the functional measures. A stepwise regression analysis was performed to (1) explore what portion of the variance in peak plantar pressure during walking can be explained by the radiographic measurements, and (2) identify structural characteristics of the foot which are significant predictors of peak plantar pressure under the heel and the first metatarsal head (MTH1). Most of the radiographic measurements were highly reliable. However, only 31 and 38% of the variance in peak plantar pressure at the heel and MTH1, respectively, could be explained using multiple regression analyses with the radiographic measurements as independent variables. Among the structural predictors that were identified, soft tissue thickness (e.g. calcaneus or sesamoid heights), and arch-related measurements were the strongest predictors of plantar pressure under both the heel and the first metatarsal head. We conclude that, in normal subjects, only about 35% of the variance in dynamic plantar pressure can be explained by the measurements of foot structure derived from radiographs. This implies that the dynamics of gait are likely to exert the major influences on plantar pressure during walking.