Plantar tissue stiffness in patients with diabetes mellitus and peripheral neuropathy

Objective: To determine if a difference exists in the plantar soft tissue of patients with diabetes mellitus (DM) and peripheral neuropathy (PN) compared with age-matched controls. Design: Case-control study with a parallel 3-element 1-dimensional viscoelastic model developed to characterize indentation data. Setting: Data collection performed in an academic physical therapy laboratory. Participants: Forty subjects were recruited into 2 groups (20 subjects with DM, PN, and history of plantar ulcers; 20 control subjects), matched for age (DM: 55.22±9.39y; control: 55.91±10.97y), gender (DM: 14 men, 6 women; control: 14 men, 6 women), and body mass index (DM: 32.96±8.39kg/m²; control: 32.58±7.69kg/m²). Interventions: The plantar soft tissue stiffness was measured over the first, third, and fifth metatarsals, and heel of each subject using an indentor system that accurately measures force/displacement (F/D) data. A parallel 3-element viscoelastic mechanical model was then used to transform the F/D data into values that were used to make stiffness assessments. Main Outcome Measures: The element coefficients of our model indicated the stiffness of the plantar tissue. Results: The plantar tissue of the subjects with DM over the metatarsal heads was stiffer than the control population as indicated by one of the spring constants in the parallel 3-element model (first: 1.13±0.55N/mm vs .72c±.32N/mm; third: .96±.32 N/mm vs .79±.17N/mm; fifth: .90±.31N/mm vs .69±.28N/mm; P<.05). Conclusions: The plantar tissue of subjects with DM, PN, and a history of ulcers was stiffer than control subjects. However, additional research is needed to determine the relationship among increased soft tissue stiffness, plantar pressures, and skin breakdown.