Individuals with Diabetes Mellitus and Neuropathy (DN) are at increased risk for ulcer development at sites exposed to repetitive, high plantar loading. Limited joint mobility may contribute to increased forefoot loading by limiting foot flexibility and restraining the forward progression of body weight during the stance phase of gait. However data substantiating the causes and consequences of limited mobility in forefoot loading is limited. The purpose of this study was to compare plantar fascia thickness, passive and active 1^st metatarsal (Met) mobility and loading in patients with and without DN.

All procedures were approved by the Institutional Review Board at the University of Iowa Hospitals and Clinics. 15 subjects with DN and 15 non-diabetic, age and gender matched control subjects participated in this study. Sagittal T1 scans were acquired using a 3T Trio scanner (Siemens Corp). Plantar fascia thickness was measured using ImageJ. Passive 1^st Met mobility and stiffness were measured using the device described by Glasoe et al. 1 Foot mobility during walking was captured using a two-segment model tracking the 1^st Met and calcaneus. Kinematic data were collected at 120 Hz, using 3 iReds on each segment (Optotrak, NDI, CAN), plantar loading data were collected at 50 Hz using a pedobarograph (EMed, Novel Inc). Kinematic data were low-pass filtered using a fourth order butterworth filter with cut-off frequencies of 6 Hz and processed using Visual3D (C-motion Inc., MD). Motion of the distal segment was expressed relative to the proximal segment using Euler angles. For kinematic data, stance phase mean was subtracted from pattern to correct for systematic offsets.

Subjects with DN showed increased plantar fascia thickness, decreased passive 1^st Met mobility and increased passive 1^st Met stiffness. Subjects with DN showed reduced 1^st metatarsal sagittal, transverse and frontal motion and increased medial forefoot loading (Table 1).

Plantar fascia thickness was negatively associated with passive 1^st Met mobility (r = -0.40, p < 0.05) when considering both groups together (n = 30). In subjects with DN, 1^st Met sagittal motion was negatively associated with peak pressure sustained under the medial forefoot (r = -0.42 and -0.06, DN and Ctrl respectively, p = 0.02).

Our results indicate that increased plantar fascia thickness limits passive first Met mobility. However we did not find evidence that passive 1^st Met mobility or stiffness influences 1^st Met mobility during gait. In individuals with DN, loss of sagittal 1^st Met mobility correlated with increased medial forefoot loading, highlighting the importance of 1^st Met mobility during functional activities.