A foot arch is a multi-segmented curved structure which acts as a spring during locomotion. It is well known that ligaments are important components contributing to this spring-like property of the arch. In addition, intrinsic and extrinsic foot muscles contribute to arch support. According to the windlass foot model, arch height and midfoot joint orientation change during gait. However, it is not known whether altered joint configurations result in increased joint stress during gait. If so, it is possible for there to be a “vicious cycle” in which joint stress increases as the arch height diminishes, which may then lead to further increases in joint stresses and eventual bone destruction.

The purpose of this study was to examine joint pressure differences of the midfoot in normal and diabetic feet during walking simulation using a robotic system. This study focused on the relative importance of muscles, ligaments and bony structures. Sixteen cadaver foot specimens were used in this study. Joint pressures were measured dynamically during full stance at four medial locations (the first cuneometatarsal, medial cuneonavicular, middle cuneonavicular, and first intercuneiform). Human gait at 25% typical walking speed and 66.7% body weight was simulated with the Universal Musculoskeletal Simulator.

It was shown that diabetic cadaver feet had, on average, a 46% higher peak in pressures, than control cadaver feet across all four tested joints. There were inverse correlations between the arch height and the peak joint pressure during the simulated arch collapse. It was proven that the acquired flat foot, caused by the tibialis posterior dysfunction, caused medial peak joint pressure increase by 12% across all tested joints.

These results could be used in furthering our understanding of the etiology of diabetic foot diseases. Also, these findings could suggest better treatment for diabetic patients, who are at risk for Charcot foot abnormalities.