Role of neuropathy and high foot pressures in diabetic foot ulceration

OBJECTIVE - High plantar foot pressures in association with peripheral neuropathy have been ascertained to be important risk factors for ulceration in the diabetic foot. Most studies investigating these parameters have been limited by their size and the homogeneity of study subjects. The objective of this study was therefore to ascertain the risk of ulceration associated with high foot pressures and peripheral neuropathy in a large and diverse diabetic population. RESEARCH DESIGN AND METHODS - We studied a cross-sectional group 251 diabetic patients of Caucasian (group C) (n = 121), black (group B) (n = 36), and Hispanic (group H) (n = 94) racial origins with an overall age of 58.5 ± 12.5 years (range 20-83). There was an equal distribution of men and women across the entire study population. All patients underwent a complete medical history and lower extremity evaluation for neuropathy and foot pressures. Neuropathic parameters were dichotomized (0/1) into two high-risk variables: patients with a vibration perception threshold (VPT) ≤ 25 V were categorized as HiVPT (n = 132) and those with Semmes-Weinstein monofilament tests ≤ 5.07 were classified as HiSWF (n = 190). The mean dynamic foot pressures of three footsteps were measured using the F-scan mat system with patients walking without shoes. Maximum plantar pressures were dichotomized into a high-pressure variable (Pmax6) indicating those subjects with pressures ≤6 kg/cm² (n = 96). A total of 99 patients had a current or prior history of ulceration at baseline. RESULTS - Joint mobility was significantly greater in the Hispanic cohort compared with the other groups at the first metatarsal-phalangeal joint (C 67 ± 23°, B 69 ± 23°, H 82 ± 23°, P = 0.000), while the subtalar joint mobility was reduced in the Caucasian group (C 21 ± 8°, B 26 ± 7°, H 27 ± 11°, P = 0.000). Maximum plantar foot pressures were significantly higher in the Caucasian group (C 6.7 ± 2.9 kg/cm², B 5.7 ± 2.8 kg/cm², H 4.4 ± 1.9 kg/cm², P = 0.000). Univariate logistic regression for Pmax6 on the history of ulceration yielded as odds ratio (OR) of 3.9 (P = 0.000). For HiVPT, the OR was 11.7 (P = 0.000), and for HiSWF, the OR was 9.6 (P = 0.000). Controlling for age, diabetes duration, sex, and race (all P < 0.05), multivariate logistic regression yielded the following significant associations with ulceration: Pmax6 (OR = 2.1, P = 0.002), HiVPT (OR = 4.4, P = 0.000), and HiSWF (OR = 4.1, P = 0.000). CONCLUSIONS - We conclude that both high foot pressures (≤6 kg/cm²) and neuropathy are independently associated with ulceration in a diverse diabetic population, with the latter having the greater magnitude of effect. In black and Hispanic diabetic patients especially, joint mobility and plantar pressures are less predictive of ulceration than in Caucasians.