Development of rotation-inducing insoles for the lower leg

Osteoarthritis of the knee (knee OA) is a prevalent condition that negatively impacts a patient's quality of life by affecting various aspects of daily living, including ambulation, mental health, and sleep. Although several engineering treatments for knee OA have been developed, no orthotic device has been successfully implemented owing to challenges such as cost, size, and aesthetic concerns. The present study aimed to develop a cost-effective and aesthetically unobtrusive tool for the prevention and treatment of knee OA. Recent studies have focused on rotational movements of the lower leg in knee OA, demonstrating that inducing such movements may be effective in preventing and alleviating knee OA by reducing the knee adduction moment. In this study, we propose a novel insole-based tool with low manufacturing costs that can be embedded into shoes without altering the appearance of the shoes. This device incorporates a rotational guidance mechanism that generates rotational motion when the body weight is applied to the insole. This mechanism uses the force applied during normal walking; therefore, it does not require external power and allows the production of lightweight devices. Initially, finite element method (FEM) simulations were conducted to establish the correlation between the internal configuration of the rotation-inducing mechanism and resulting rotation angle. Based on these findings, a prototype of the rotation-inducing mechanism was fabricated and its rotational angle and stability were comprehensively evaluated. Finally, an insole incorporating the rotation-inducing mechanism (rotation-inducing insole) was developed, and a series of experiments were conducted to assess its effect on walking. The results showed that the rotation-inducing mechanism can adjust the rotation angle by modifying its internal structure. By adjusting the rotation angle, the mechanism can be applied to treat symptoms of varying severity. In addition, rotation-inducing insoles promoted external rotation of the lower leg during gait and affected walking patterns. These findings suggest that utilizing rotation-inducing insoles to control lower leg rotational movement could contribute to the prevention and improvement of knee OA.