Multi-material, Layer, and Density Insoles for a Patient-specific Approach to Shear and Pressure Reduction in the Treatment and Prevention of Diabetes-related Foot Ulcer

Device Description: The Dynamic Foot Orthosis (DFO) is designed with a rolling link mechanism at the distal 3rd. It is designed to reduce sliding friction and torque at the metatarsal heads in addition to decreasing compressive forces that is accomplished by the conventional multi-durometer FOs. The relative sliding motion of two compliant surfaces over each other allows some deformation horizontally and lowers frictional resistance. The DFO addresses the friction element by accommodating the normal sliding and rolling motion at the distal 3rd of the foot during gait. Additionally, the DFO has a silicone layer at the metatarsal head and the remainder of the anterior section made of 2 separated orthotic layers that slide over each other. This provides an articulating surface to provide a relative motion between the orthotic segments while transmitting load.

Study Objectives: In this pilot study, the first objective is to bench test a novel shear reducing insole and compare it to current standard insoles and shoes. The second objective is to study twenty-seven insensate diabetes patients with pre-ulcerative foot callus to examine for changes in spatial temporal gait including gait initiation, risk of falling, static and dynamic balance, and plantar temperature response to walking and consecutive plantar stress in both footwear conditions.

Study Design: This is an interventional study. For objective one, changes in compression stiffness and static coefficients of friction will be measured using a force dynamometer in the lab of Professor Albert Shih. A test platform will be built to evaluate the performance of the shear reduction shoe sole design and characteristic of the force, in two directions parallel (shear) and perpendicular to the ground, and the associated deformation under the steady-state and impulse conditions.

For objective two, diabetes patients presenting to the Michigan Orthotics and Prosthetics Center for fabrication and dispensing of diabetic shoes and innersoles will be invited to participate. Twenty-seven insensate diabetes patients with pre-ulcerative foot callus will be enrolled. Patients will wear body worn sensors (LegSys) to measure changes in spatial-temporal gait and static and dynamic balance parameters prior and post usage of the insoles. To reduce the effects of learning from naïve use of novel footwear, the testing sequence between the experimental and standard footwear will be randomized. We will examine increase on foot temperature over 200 steps of continuous walking using the DFO and using standard insoles. We will also examine if the thermal changes are mediated by autonomic neuropathy as measured by sudomotor function. The footwear testing sequence will be randomized and an acclimatization procedure will be followed in an effort to minimize the potential effects of cumulative plantar temperature responses to walking and footwear conditions. We will also examine static balance by measuring center of mass with eyes open and eyes closed condition.

Outcome Measures: For objective one, the primary endpoints will be the compression stiffness and static coefficients of friction. For objective two, plantar foot temperature changes in regions-of-interest in response to walking 200 steps will be measured in each footwear condition and compared to baseline. Other outcome measures include gait analysis, including gait initiation, gait speed, double support time, medial and lateral center of mass displacement, and inter-cycle variability under single and dual task conditions. This will be measured during each footwear condition. Static balance will also be measured in each footwear condition. Using the Romberg's test, we will also assess center of mass displacement and reciprocal hip and ankle motion under eyes open and closed conditions. Sudomotor function will be measured by electrical sweat conductance (ESC), as expressed in microSiemens (µS).