Effect of a carbon reinforcement for maximizing shoe outsole bending stiffness on plantar pressure and walking comfort in people with diabetes at high risk of foot ulceration

Background: Different shoe design features can reduce peak plantar pressure to help prevent foot ulcers in people with diabetes. A carbon reinforcement of the shoe outsole to maximize bending stiffness is commonly applied in footwear practice, but its effect has not been studied to date. Research question: What is the effect of a carbon shoe-outsole reinforcement on peak plantar pressure and walking comfort in people with diabetes at high risk of foot ulceration? Methods: In 24 high-risk people with diabetes, in-shoe regional peak pressures were measured during walking at a comfortable speed in two different shoe conditions: an extra-depth diabetes-specific shoe with a non-reinforced outsole and the same type of shoe with a 3-mm-thick full-length carbon reinforcement of the outsole. The same custom-made insole was worn in both shoe conditions. Walking comfort was assessed using a Visual Analogue Scale (0–10, 10 being highest possible comfort). Results: Significantly lower metatarsal head peak pressures (by a median 10–22 kPa) were found with the reinforced shoe compared to the non-reinforced shoe (p < .001). In >83% of cases with the reinforced shoe and >71% with the non-reinforced shoe metatarsal head peak pressures were <200 kPa. At the hindfoot, peak pressures were significantly higher (by a median 24 kPa) with the reinforced shoe (p = .001). No significant shoe effects were found for the toes. No significant shoe effects were found for walking comfort: median 6.1 for the reinforced shoe versus 5.6 for the non-reinforced shoe. Significance: Adding a full-length carbon reinforcement to the outsole of a diabetes-specific shoe significantly reduces peak pressures at the metatarsal heads, where ulcers often occur, in high-risk people with diabetes, and this does not occur at the expense of patient-perceived walking comfort.