In-shoe pressure measurement and foot orthosis research: a giant leap forward or a step too far?

Foot orthoses are believed to exert their therapeutic effect on the human locomotor apparatus by altering the location, magnitude, and temporal patterns of ground reaction forces acting on the plantar foot during weightbearing activities. In-shoe pressure-measurement systems are increasingly being used by clinicians and researchers to assess kinetic changes at the foot-orthosis interface to better understand the function of foot orthoses and to derive more efficacious treatments for many painful foot and lower-extremity abnormalities. This article explores how the inherent three-dimensional surface topography and load-deformation characteristics of foot orthoses may challenge the validity, reliability, and clinical usefulness of the data obtained from in-shoe pressure-measurement systems in the context of foot orthotic therapy and research.

Effect of 7-degree rearfoot varus and valgus wedging on rearfoot kinematics and kinetics during the stance phase of walking.

Background: The scientific evidence behind the mechanical function of foot orthoses is still controversial. Research studies that have investigated the kinematic effect of foot orthoses on the lower extremity have shown variable results, with orthoses causing either no significant change or a small significant change in foot kinematics.

Methods: The right limbs of 12 healthy asymptomatic individuals were studied in three walking conditions: barefoot, with a 7 degrees rearfoot varus wedge, and with a 7 degrees rearfoot valgus wedge.

Static response of maximally pronated and nonmaximally pronated feet to frontal plane wedging of foot orthoses.

Background: Research on foot orthoses has shown that their effect on the kinematics of the rearfoot is variable, with no consistent patterns of changes being demonstrated. It has also been hypothesized that the mechanical effect of foot orthoses could be subject specific. The purpose of our study was to determine if maximally pronated feet have a different response to frontal plane wedging of foot orthoses than do nonmaximally pronated feet during static stance.

In vivo tests of an improved method for functional location of the subtalar joint axis.

The subtalar joint is important in frontal plane movement and posture of the hindfoot. Abnormal subtalar joint moments caused by muscle forces and the ground reaction force acting on the foot are thought to play a role in various foot deformities. Calculating joint moments typically requires knowledge of the location of the joint axis; however, location of the subtalar axis from measured movement is difficult because the talus cannot be tracked using skin-mounted markers.

The subtalar joint axis locator: a preliminary report.

A new clinical device, the subtalar joint axis locator, was created to track the three-dimensional location of the subtalar joint axis during weightbearing movements of the foot. The assumption was that if the anterior exit point of the subtalar joint axis is stationary relative to the dorsal aspect of the talar neck, then, by performing radiographs of the feet with the subtalar joint axis locator in place on the foot, the ability of the locator to track rotations and translations of the talar neck and thus the subtalar joint axis in space could be approximated. In this preliminary study of two adults, the subtalar joint axis locator accurately tracked the talar neck position during weightbearing rotational motions of the subtalar joint.

Determination of subtalar joint axis location by restriction of talocrural joint motion.

The location of the subtalar joint axis is an important determinant of the mechanical function of the foot. The moments of muscle forces and of the ground reaction force about the subtalar joint are dependent upon the location of this joint axis. There is substantial variation in subtalar axis location across subjects, but current methods for determining its location are often invasive or involve expensive imaging protocols.

Effects of simulated genu valgum and genu varum on ground reaction forces and subtalar joint function during gait.

The mechanical effects of genu valgum and varum deformities on the subtalar joint were investigated. First, a theoretical model of the forces within the foot and lower extremity during relaxed bipedal stance was developed predicting the rotational effect on the subtalar joint due to genu valgum and varum deformities. Second, a kinetic gait study was performed involving 15 subjects who walked with simulated genu valgum and genu varum over a force plate and a plantar pressure mat to determine the changes in the ground reaction force vector within the frontal plane and the changes in the center-of-pressure location on the plantar foot.

Reliability and accuracy of biomechanical measurements of the lower extremities.

The reliability of biomechanical measurements of the lower extremities, as they are commonly used in podiatric practice, was quantified by means of intraclass correlation coefficients (ICCs). This was done not only to evaluate interrater and intrarater reliability but also to provide an estimate for the accuracy of the measurements. The measurement protocol involved 30 asymptomatic subjects and five raters of varying experience.