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

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™ (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.