Calcaneal movement measured by skin versus shoe-mounted markers

Pronation or foot movement - What is important

OBJECTIVES

Despite difficulties to quantify foot pronation non-invasively and during dynamic tasks, pronation was frequently discussed with respect to injury risk and footwear development. Typically, surrogate measures were used to approximate the movement of pronation showing inconsistent results due to the high variability in the methodology and protocols. This study determines the relationships between all identified pronation variables and aims to reduce the data set to its dominant factors.

DESIGN

Cross-sectional.

METHODS

Forty barefoot participants (14 F, 26 M) performed four standing tasks (subneutral, bipedal, single-leg with 20° and single-leg with 30° knee flexion), over ground walking (1.5m/s) and running (3.5m/s) trials. Manual assessment data, motion capture data, ground reaction forces, and plantar pressure distributions were collected. Sixty-one commonly used pronation measures were compared using Spearman Correlations and a Principal Component Analysis (PCA).

RESULTS

Two groups of correlated variables were found, 4.2% of them correlated mainly with the longitudinal arch angle (LAA), the other 10.2% correlated with the Achilles tendon angle (β). The remaining 85.6% were not significantly correlated to each other.

CONCLUSIONS

The LAA is representative for the movement of the mid foot and β quantifies rear foot eversion relative to the shank. Since these dominant variables varied independently from each other, both cannot quantify pronation simultaneously. Therefore, it is important to consider and report both, LAA-pronation and β-pronation separately to represent prevalent foot movement properties. Separately assessing the two dominant underlying mechanisms of foot movement may lead to improved guidelines for clinical screening and footwear manufacturing.

Relationships between the foot posture Index and static as well as dynamic rear foot and arch variables

Clinicians, podiatrists and researchers have been quantifying foot posture and movement in various speed conditions and populations. Common variables to assess foot posture/movement are the Foot Posture Index (FPI-6), Achilles tendon angle (β), rear foot angle (γ) and longitudinal arch angle (LAA). These variables were frequently used in clinical and biomechanical settings. This study aimed to determine the relationship between the biomechanical variables (β, γ & LAA) in static and dynamic conditions and the clinically used FPI-6 and their redundancy. Forty participants performed bipedal standing, over ground walking and running trials. Manual assessment data (FPI-6), kinematic data and ground reaction forces were collected. Discrete biomechanical variables (β, γ & LAA) were calculated at various time points (e.g. heel strike). A Principal Component Analysis (PCA) was performed to quantify the contribution of each variable to the overall variance in the data set. Spearman correlations were used to assess the relationship between the sub-measures of the FPI-6 and the biomechanical variables. Two major components were found that explained 85.2% of the overall variance, consisting of LAA and β variables, respectively. Only LAA variables showed significant, but moderate correlations (r < -0.6) with the fifth sub-measurement of the FPI-6. The LAA and β describe independent movements, which dominate foot posture/movement in static and dynamic conditions. The FPI-6 sub-measurements did not closely reflect static nor dynamic behavior of the rear and mid foot. The FPI-6 and biomechanical variables may not be used interchangeably for screening or grouping individuals according to their foot posture/movement.