Response: Letter to the Editor

Dear Dr Curran,

A recent letter to the editor has given us the opportunity to further elaborate about the results of our study. ¹ The authors greatly appreciate Michael Dillon and Stefania Fatone for taking an interest in our article. They speculated that the toe plates of the ankle–foot orthoses (AFOs) in our study were too compliant to normalize center of pressure (CoP) excursion or restore the effective foot length, which is an apparent contradiction to previously reported findings using forceplates.^2,3

In our study, we examined the peak plantar pressures and pressure distributions under the diabetic foot. Pressure distributions, directly under the partial foot, were measured using bipedal in-shoe F-Scan sensor system (Tekscan, South Boston, MA). The sensors were taped on top of flat 1/8″ insoles that were placed inside the shoe and on top of the footplate of the AFO. Flat insoles were used to reduce variability between the shoe-only condition and the shoe-with-Blue-Rocker condition, and because the F-Scan sensors didn’t conform to the contours of the custom-molded partial foot insole.

When measuring the CoP with the F-Scan sensors on top of the 1/8″ insole, the CoP did not traverse beyond the distal end of the foot, during either condition. ¹ In fact, this pilot study found that during late stance, the CoP remained further behind the distal end of the residuum while wearing the Blue Rocker AFO as compared to the shoe-only condition. ¹ During late stance when the AFO resists ankle dorsiflexion, load transfers from the anterior shell to the forefoot section of the AFO. The force plate under the shoe would directly measure this load. However, the F-scan sensor only registered pressure under the foot on top of the AFO footplate inside of the shoe. There was no toe filler, and there was nothing to exert force beyond the distal end of the foot. It could be expected that the CoP trajectory derived using ground reaction force plates could be different than that derived from in-shoe pressure sensors. These methodological differences could readily explain differences in findings of these studies.

These questions of how to restore the effective foot length, improve gait kinetics/kinematics and better distribute the peak plantar pressures are equally important in clinical practice. Findings from both methodologies support the beneficial role of above-ankle orthoses toward improving function by reducing distal residuum pressures and extending effective foot length. However, more research is warranted to clarify the in-shoe pressure distribution to aid clinical decision-making. Many clinical questions remain about fitting an above-ankle or a below-ankle orthosis on individuals with transmetatarsal amputations due to neuropathy.