A new device for foot sensory examination employing auto-presentation of shear force stimuli against the skin

Abstract

A new plantar foot sensation-testing instrument (PFS Tester) was developed for the practical screening of diabetic neuropathy and the prediction of fall risk for frail elderly people. Human plantar sensation may play an important role in many processes, including postural control, walking, and the clinical testing of diabetic peripheral neuropathy. The PFS Tester uses shear force on the skin as the mechanical stimulus, unlike any existing devices or tools for sensory examination, and it automatically provides the test site on the plantar foot with a pre-programmed sequence of stimuli. Although the PFS Tester uses two factors to distinguish stimulus intensity (a variable range and the speed of the shearing movement), measurements of the shear force on a material that simulates a human body showed that only a range of the probe movement affected the stimulus intensity. Also, the increment profiles of twenty-grade stimulus of the PFS Tester were similar to those of the Semmes-Weinstein (SW) monofilament, which is the most typical sensory exam tool. In addition, repetitive measurements of the force using the PFS Tester and the SW monofilament showed that the stimulus intensity of the PFS Tester had better reproducibility than that of the SW monofilament. To verify the validity of the sensory examination's results of the PFS Tester, sensory thresholds on three sites of the plantar foot in nineteen subjects with diabetes mellitus were measured using the SW monofilament test and the PFS Tester. The sensory thresholds obtained by the PFS Tester had a favorable correlation to those obtained by the SW monofilament test. The results of this study demonstrated that a PFS Tester could be used as a simple sensory examination machine with good reliability, simplified operation, and a high compatibility with the SW monofilament test.