The external force associated with callus formation under the first metatarsal head is reduced by wearing rocker sole shoes

Introduction: Callus is one of the main causes of diabetic foot ulcers. Therefore, preventing callus formation is very important. In a previous study, it was clarified that callus formation under the first metatarsal head (MTH) is associated with high shear stress time integral/pressure time integral (SPR-i). another study, it was clarified that rocker sole shoes are effective in reducing peak pressure under the first MTH. Therefore, we hypothesized that rocker sole shoes reduce SPR-i under the first MTH. This study aimed to clarify the effect of rocker sole shoes for external forces and leg motions in comparison with that of the normal sole shoes. Methods: In-shoe external forces and leg motions were measured during walking wearing the normal sole shoes or the rocker sole shoes in healthy participants. As the external forces, the peak plantar pressure (PP), pressure time integral (PI), peak shear stress (PSS), and shear stress integral (SSI) of each gait cycle were calculated. Additionally, shear stress-pressure ratios (SPR) were calculated by dividing shear stress by pressure; concretely, peak values (SPR-p) and time integral values (SPR-i). As the leg motion, hip and knee joint motions were analyzed for the axis of flexion- extension. Three axes of ankle joint motion (inversion-eversion, plantar flexion-dorsiflexion, and adduction-abduction) were analyzed. Results and Discussion: Six participants attended, and twelve feet were analyzed. When wearing the rocker sole shoes, the SPR-i under the first MTH was significantly smaller than when wearing the normal sole shoes. The SPR-i higher than 0.60 is associated with callus formation under the first MTH. In three of five feet with callus, SPR-i exceeded 0.60 in the normal sole shoes. The SPR-i of all three feet became smaller than 0.60 when wearing the rocker sole shoes. Although the knee (flexion-extension) and ankle (plantar flexion-dorsiflexion) joint motion became smaller when wearing the rocker sole shoes, there was no significant difference in walking speed. It is considered that propulsion was maintained by the push-off support provided by rocker sole shoes. Conclusion: It was suggested that rocker sole shoes are effective preventing callus formation under the first MTH.

I. Introduction

Callus is one of the main causes of diabetic foot ulcers. Many foot ulcers progress to lower limb amputation and can seriously affect the quality of life (QOL), reduce physical activity, and increase psychological stress [1]. In addition, even when an ulcer has successfully healed, the risk of recurrence is high, with reported rates ranging between 30% and 40% within one year [2]. Therefore, the prevention of foot ulcers is of paramount importance and has long been recognized as a priority by the International Working Group on the Diabetic Foot (IWGDF) [3].