Effects of extended stance time on a powered knee prosthesis and gait symmetry on the lateral control of balance during walking in individuals with unilateral amputation.
Andrea Brandt, He Helen Huang
PMID 31783759WHAT IT FOUND
Visual feedback helped six people with leg amputations walk more symmetrically on a powered prosthesis.
However, this increased side-to-side body sway and hip muscle effort, and reduced their stability margin on the prosthetic side, suggesting symmetry comes at a balance cost.
Key findings
01Visual feedback targeting longer stance time significantly improved stance time symmetry by 20% compared to no feedback.
02Increasing stance time on the prosthetic side significantly decreased the lateral margin of stability, indicating reduced dynamic balance.
03Participants increased hip abductor muscle activity and medial-lateral center-of-mass excursion to manage the balance demands of longer stance times.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The sample size was extremely small (n=6), limiting generalizability. Participants had very limited training time with the powered prosthesis (only two sessions), which may not reflect established use. Different prosthetic ankle components were used across subjects, introducing potential confounds in balance mechanics. The alpha level was set at 0.1 (less conservative than standard 0.05) to reduce Type II error risk, which increases the chance of false positives. The study was conducted on a treadmill at self-selected speeds, which may not fully replicate overground walking demands.
Declared interests
Funding was provided by the National Science Foundation and the National Institute of Health. No commercial conflicts of interest were declared in the text, though the study used a commercial powered knee prosthesis (Power Knee).
The easy way to misread this
Do not interpret the improved stance time symmetry as a clear clinical win. The study shows this symmetry came with a significant decrease in lateral stability and increased muscular effort, which might make the gait pattern harder to maintain outside the lab or riskier for patients with compromised balance.