Changes in sub-calcaneal fat pad composition and their association with dynamic plantar foot pressure in people with diabetic neuropathy

Background: Diabetic foot disease is associated with physiological and biomechanical abnormalities in the foot that increase risk for ulceration. The objective was to assess MRI changes in the composition of sub-calcaneal fat pad tissue and its association with plantar pressure during walking. Methods: Fourteen people with diabetes and peripheral neuropathy and five age-matched healthy controls underwent T1-weighted sagittal plane spin-echo Dixon MRI of the rearfoot. Dixon Chemical Shift Imaging was used to create fat-only and water-only images from which the fat signal fraction in a defined ROI of the sub-calcaneal fat pad was calculated. Barefoot plantar pressure distribution during walking was assessed and associated with fat pad outcomes. Findings: Mean ± SD fat signal fraction was significantly lower in the neuropathic subjects than in the healthy controls (0.55 ± 0.11 vs. 0.72 ± 0.03, p < 0.005), and was explained by a lowering in fat signal (R ² 0.87), more than an increase in water signal (R ² 0.32). Mean ± SD peak pressure at the heel was 391 ± 119 kPa for the neuropathic subjects and 325 ± 53 kPa for the healthy controls (non-significantly different). Fat signal fraction and peak pressure were significantly inversely correlated (r = −0.59, p < 0.01). Interpretation: Dixon chemical shift MRI showed a reduced fat signal fraction in sub-calcaneal fat pad tissue in people with diabetic neuropathy. Both neuropathic and non-neuropathic factors may be attributed to this outcome. Fat pad function also seems to be compromised, as indicated by an associated increase in peak plantar pressures. This may increase risk for foot ulceration.