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PLoS One. 2018 Sep 26;13(9):e0204512. doi: 10.1371/journal.pone.0204512. eCollection 2018.

Bimodal ankle-foot prosthesis for enhanced standing stability.

Author information

Minneapolis Department of Veterans Affairs Health Care System, Minneapolis, MN, United States of America.
Division of Rehabilitation Science, Department of Rehabilitation Medicine, University of Minnesota, Minneapolis, MN, United States of America.


Previous work suggests that to restore postural stability for individuals with lower-limb amputation, ankle-foot prostheses should be designed with a flat effective rocker shape for standing. However, most commercially available ankle-foot prostheses are designed with a curved effective rocker shape for walking. To address the demands of both standing and walking, we designed a novel bimodal ankle-foot prosthesis that can accommodate both functional modes using a rigid foot plate and an ankle that can lock and unlock. The primary objective of this study was to determine if the bimodal ankle-foot system could improve various aspects of standing balance (static, dynamic, and functional) and mobility in a group of Veterans with lower-limb amputation (n = 18). Standing balance was assessed while subjects completed a series of tests on a NeuroCom Clinical Research System (NeuroCom, a Division of Natus, Clackamas, OR), including a Sensory Organization Test, a Limits of Stability Test, and a modified Motor Control Test. Few statistically significant differences were observed between the locked and unlocked ankle conditions while subjects completed these tests. However, in the absence of visual feedback, the locked bimodal ankle appeared to improve static balance in a group of experienced lower-limb prosthesis users whose PLUS-M mobility rating was higher than approximately 73% of the sample population used to develop the PLUS-M survey. Given the statistically significant increase in mean equilibrium scores between the unlocked and locked conditions (p = 0.004), future testing of this system should focus on new amputees and lower mobility users (e.g., Medicare Functional Classification Level K1 and K2 prosthesis users). Furthermore, commercial implementation of the bimodal ankle-foot system should include a robust control system that can automatically switch between modes based on the user's activity.

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Conflict of interest statement

I have read the journal's policy and the authors of this manuscript have the following competing interests: Several of the authors are co-investigators on grants to develop ankle-foot prostheses that are designed to lock and unlock for different standing and walking activities: Department of Veterans Affairs, Rehabilitation Research and Development (RR&D) Service, Merit Review Award # I01 RX002267 (awarded to SRKM). The following authors have patents related to the bimodal ankle-foot system: United States Patent 8,764,850. Issued July 1, 2014: AHH. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

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