Are clinical measures of foot posture and mobility associated with foot kinematics when walking?

Background: There is uncertainty as to which foot posture measures are the most valid in terms of predictingkinematics of the foot. The aim of this study was to investigate the associations of clinical measures of static footposture and mobility with foot kinematics during barefoot walking. Method: Foot posture and mobility were measured in 97 healthy adults (46 males, 51 females; mean age 24.4 ±6.2 years). Foot posture was assessed using the 6-item Foot Posture Index (FPI), Arch Index (AI), Normalised NavicularHeight (NNHt) and Normalised Dorsal Arch Height (DAH). Foot mobility was evaluated using the Foot Mobility Magnitude(FMM) measure. Following this, a five-segment foot model was used to measure tri-planar motion of the rearfoot,midfoot, medial forefoot, lateral forefoot and hallux. Peak and range of motion variables during load acceptance andmidstance/propulsion phases of gait were extracted for all relative segment to segment motion calculations. Hierarchicalregression analyses were conducted, adjusting for potential confounding variables. Results: The degree of variance in peak and range of motion kinematic variables that was independently explained byfoot posture measures was as follows: FPI 5 to 22 %, NNHt 6 to 20 %, AI 7 to 13 %, DAH 6 to 8 %, and FMM 8 %. The FPIwas retained as a significant predictor across the most number of kinematic variables. However, the amount of varianceexplained by the FPI for individual kinematic variables did not exceed other measures. Overall, static foot posturemeasures were more strongly associated with kinematic variables than foot mobility measures and explained morevariation in peak variables compared to range of motion variables. Conclusions: Foot posture measures can explain only a small amount of variation in foot kinematics. Static foot posturemeasures, and in particular the FPI, were more strongly associated with foot kinematics compared with foot mobilitymeasures. These findings suggest that foot kinematics cannot be accurately inferred from clinical observations of footposture alone