Pressure Relief and Load Redistribution by Custom-made Insoles in Diabetic Patients with Neuropathy and Foot Deformity

Objective: To study the effects of custom-made insoles on plantar pressures and load redistribution in neuropathic diabetic patients with foot deformity.

Design: Cross-sectional.

Background: Although custom-made insoles are commonly prescribed to diabetic patients, little quantitative data on their mechanical action exists.

Methods: Regional in-shoe peak pressures and force-time integrals were measured during walking in the feet of 20 neuropathic diabetic subjects with foot deformity who wore flat or custom-made insoles. Twenty-one feet with elevated risk for ulceration at the first metatarsal head were analysed. Load redistribution resulting from custom-made insoles was assessed using a new load-transfer algorithm.

Results: Custom-made insoles significantly reduced peak pressures and force-time integrals in the heel and first metatarsal head regions; pressures and integrals were significantly increased in the medial midfoot region compared with flat insoles. Custom-made insoles successfully reduced pressures in and integrals at the first metatarsal head in 7/21 feet, were moderately successful in another seven, but failed in the remaining seven. Load transfer was greatest from the lateral heel to the medial midfoot regions.

Conclusions: Custom-made insoles were more effective than flat insoles in off-loading the first metatarsal head region, but with considerable variability between individuals. Most off-loading occurred in the heel (not a region typically at risk). The load transfer algorithm effectively analyses custom-made-insole action.

Relevance: Because similar insole modifications apparently exert different effects in different patients, a comprehensive evaluation of custom designs using in-shoe pressure measurement should ideally be conducted before dispensing insoles to diabetic patients with neuropathy and foot deformity.