Comparing plantar shear strain in patients with a previous diabetes-related foot ulcer and those at low risk for ulceration using the STrain Analysis and Mapping of the Plantar Surface (STAMPS) system.

Abstract

BACKGROUND: STrain Analysis and Mapping of the Plantar Surface (STAMPS) is an innovative system using a plastically deformable insole with a stochastic speckle pattern, developed to measure peak plantar shear strain (SMAG) in people with diabetes. The aim was to determine whether patients with a prior DFU exhibit higher SMAG than low-risk patients. METHODS: Participants walked 20 steps with the STAMPS insole within a standardised shoe and 10 m with the Pedar-X TM (Novel, Inc.) measurement insole. SMAG was compared in participants with either a recently healed diabetic foot ulcer (Prior DFU group) or diabetes and low risk for ulceration (NICE NG-19). Measurements were repeated three times. Images were analysed using the DIC software 'GOM correlate' (Zeiss, Inc.) and post-processed using MATLAB. Outcomes were overall and regional peak SMAG and peak plantar pressure (PPP). Consenting prior DFU participants subsequently repeated the walking assessments wearing a diabetic below-knee walker-boot. Overall and regional peak SMAG and PPP were compared between the standard shoe and walker-boot. RESULTS: Twenty participants with prior DFU and 14 at low risk were recruited. Overall peak SMAG within the prior DFU and low-risk groups was 27.9% (IQR - 17.3-37.5%) and 11.5% (IQR 9.6-20.3%) respectively, p = 0.003. Within the prior DFU group, SMAG was elevated at DFU sites compared with non-DFU sites; peak SMAG was 11.7% (IQR 7.6-25.6%) and 7.70% (4.4-13.1%). Sixteen participants completed the offloading assessments. Peak SMAG within the standard shoe and walker-boot was 27.4% (IQR 17.2-32.7) and 8.03% (IQR 6.3-12.2). CONCLUSION: Participants with a recently healed DFU exhibited elevated strain characteristics compared with the low-risk group. Furthermore, prospective work will explore the relationship between SMAG and DFU formation.