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. The inability of in-shoe pressure-measurement systems to measure shearing forces beneath the foot, the required bending of the flat two-dimensional sensor insole to fit the pressure insole to the three-dimensional curves of the orthosis, the subsequent unbending of the sensor insole to display it on a computer monitor, and variations in the load-deformation characteristics of orthoses are all sources of potential error in examination of the kinetic effects of foot orthoses. Consequently, caution is required when interpreting the results of orthotic research that has used in-shoe pressure insole technology. The limitations of the technology should also be given due respect when in-shoe pressure measurement is used to make clinical decisions and prescribe custom foot orthoses for patients.

Effect of extrinsic rearfoot post design on the lateral-to-medial position and velocity of the center of pressure.

Findings from investigations of the effects of external forefoot and rearfoot posts added to foot orthoses have been inconclusive. This study was undertaken to examine the effects of rearfoot post design on the lateral-to-medial position and velocity of the center-of-pressure path. Four identical pairs of neutral-cast polypropylene orthotic shells were constructed; three pairs had a rearfoot post of specified design added. The fourth pair, the control, did not have a post added. Stance period data were broken down into four functional phases, and the statistically significant differences between the experimental conditions were calculated and analyzed. The addition of a rearfoot post to an orthotic shell affects center-of-pressure lateral-to-medial position and velocity. Although the effect of the post designs seemed to provide reasonably predictable changes in center-of-pressure position, the effect on center-of-pressure velocity was variable and inconsistent. The effect of the orthotic post was dependent on design and phase of gait. The addition of a rearfoot post and, specifically, the design of the post can probably be used to alter the center-of-pressure position and velocity.

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. The device was also used in a series of subjects to determine its dynamic capabilities. It is possible, then, that the subtalar joint axis locator can reliably track the spatial location of the subtalar joint axis during weightbearing movements of the foot.

The effect of 5-degree valgus and varus rearfoot wedging on peak hallux dorsiflexion during gait.

The dynamic effects of 5 degrees varus and valgus rearfoot wedging on peak hallux dorsiflexion were investigated in 30 asymptomatic subjects (5 males and 25 females). Statistically significant reductions in peak hallux dorsiflexion were found with rearfoot varus wedging and rearfoot valgus wedging. Furthermore, the reduction in peak hallux dorsiflexion occurring with rearfoot varus wedging was statistically significant compared with that associated with rearfoot valgus wedging. These findings have implications for the orthotic management of a variety of lower-limb pathologies.