“A lack of evidence of compelling clinical benefits is a key factor limiting the adoption of commercialized powered robotic knee prostheses into mainstream clinical practice,” write the authors of a new study investigating the clinical effects of the latest generation Össur Power Knee. “Previous studies have demonstrated mixed results, potentially due to a combination of limitations in prosthetic hardware, control algorithms, and testing methodologies.” Their study concluded that the Power Knee can create clinical improvements in walking and sit/stand behaviors compared to passive microprocessor knees, although the effects are sensitive to the user’s mobility level and the Power Knee’s control policy.
Seven people with transfemoral amputations and K3 or K4 mobility levels completed repeated sitting and standing, a stand, walk, sit shuttle test, and fast walking on a treadmill. The researchers tested the Power Knee’s standard control policy and a novel control policy and compared the metrics to those found with the users’ prescribed passive prostheses.
The data indicated that the clinical effects of the Power Knee varied with mobility level and the control policy used. The phase-based controller often produced stronger walking and sit/stand improvements for the higher mobility group compared to the default controller; it also presented a steeper learning curve and reduced walk-to-sit transition speed. The default control policy was perceived as easier to master but was less assistive to the higher mobility group and produced slower sit/stand cycles.
The K3 participants experienced improvements in standing speed inter-limb ground reaction force symmetry and inter-limb peak knee moment symmetry during sit-to-stand tasks relative to their passive prostheses. The K4 participants benefited less in sit/stand but showed improvements while walking, including increased toe clearance, greater early stance knee flexion and, for the novel control policy, a reduced swing-phase peak hip flexion moment.
Neither control policy produced significant benefits in endurance or repeated task performance compared to the passive condition. Sit-to-stand cycle count in the lower mobility group was unchanged, and it was reduced in the higher mobility group with the standard condition. In the shuttle walk test, laps completed by higher mobility users decreased with the novel control policy, and no significant differences were found for lower mobility users. No significant changes in fast walking distance or speed were observed across conditions.
Some negative effects of the Power Knee were also observed, including reduced agility, slower transitions, and thermal limitations, which might be addressed through future control innovations or with more thorough acclimation, according to the authors.
The open-access study, “The clinical effects of the Össur Power Knee with phase-based and default control during sitting, standing, and walking,” was published in the Journal of NeuroEngineering and Rehabilitation.
