Plantar tissue stiffness in patients with diabetes mellitus and peripheral neuropathy

Abstract

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+/-9.39 y; control: 55.91+/-10.97 y), gender (DM: 14 men, 6 women; control: 14 men, 6 women), and body mass index (DM: 32.96+/-8.39 kg/m(2); control: 32.58+/-7.69 kg/m(2)).

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 measure: 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+/-0.55 N/mm vs.72+/-.32 N/mm; third:.96+/-.32 N/mm vs.79+/-.17 N/mm; fifth:.90+/-.31 N/mm vs.69+/-.28 N/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.