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.