Relationship between diabetes-related large-fiber neuropathy and dorsiflexion range of motion at the ankle and first metatarsophalangeal joints

Background: Diabetes-related peripheral neuropathy (DPN) and limited joint mobility of the foot and ankle are implicated in the development of increased plantar pressures and diabetesrelated foot ulcers. The extent of this relationship has not been conclusively established. We aimed to determine the relationship between ankle joint and first metatarsophalangeal joint dorsiflexion range of motion and DPN using a cross-sectional observational study design. Methods: Primary outcomes were DPN status, ankle joint range of motion (extended and flexed knee lunge tests), and nonweightbearing first metatarsophalangeal joint range of motion. Correlations were performed using Pearson r, and hierarchical regression analyses were undertaken to determine the independent contribution of DPN to the variance in dorsiflexion range of motion of ankle and first metatarsophalangeal joints using standardized β regression coefficients, controlling for age, sex, body mass index, diabetes duration, and hemoglobin A_1c level. Results: One hundred one community-dwelling participants (mean ± SD age, 65.0 ± 11.2 years; 55 men; 97% type 2 diabetes; mean ± SD diabetes duration, 8.7 ± 7.8 years; 23% with DPN) were recruited. Diabetes-related peripheral neuropathy demonstrated significant correlations with reduced range of motion at the ankle joint (knee extended: r = –0.53; P < .001 and knee flexed: r = –0.50; P < .001) and the first metatarsophalangeal joint (r = –0.37; P < .001). Also, DPN made significant, unique contributions to the regression models for range of motion at the ankle joint (knee extended: r² change = 0.121; β = –0.48; P < .001 and knee flexed: r² change = 0.109; β = –0.45; P < .001) and first metatarsophalangeal joint (r² change = 0.037; β = –0.26; P = .048). Conclusions: These findings suggest that DPN contributes to reduced ankle and first metatarsophalangeal joint range of motion. Due to the established link between reduced ankle and first metatarsophalangeal joint range of motion and risk of diabetes-related foot ulcer, we recommend that clinicians assess dorsiflexion range of motion at these joints as part of routine foot assessment in people with diabetes, especially those with DPN.