Contemporary prosthetic knees include passive (mechanical), adaptive (computerized), or active (motorized) control systems and have the potential to mitigate amputation-related functional impairments and activity limitations. Researchers at the University of Washington studied physical performance and self-report outcomes associated with use of each type of knee in people with unilateral transfemoral amputations.
The study concludes that middle-aged or older members of this population may benefit from prosthetic knees with adaptive control as the most functional and desirable intervention. The findings suggest that adaptive knee control may enhance function compared with passive control, but that active control can restrict mobility in these users. Compared with passive control, adaptive control significantly improved comfortable Timed Up and Go (TUG) test time and reported physical function. Active control significantly increased comfortable TUG, fast TUG, ramp times, and increased balance confidence when compared with passive control.
During the 14-month randomized crossover trial, 12 participants who had a mean age of 58 years were tested under three prosthetic conditions: passive control (existing knee), adaptive control (Össur Rheo Knee II), and active control (Össur Power Knee II). Training and acclimation time for the adaptive and active knees were provided to the participants. Outcome measures included indoor tests (TUG, stairs, and ramp), outdoor tests (walking course and perceived exertion), step activity monitor, self-report surveys (mobility, balance confidence, physical function, fatigue, and general health), and fall incidence.
Adaptive knee control, as implemented in the Össur Rheo Knee II, significantly improved users’ mobility at self-selected walking speeds and perceived function in daily activities, but limited the speed with which they ascended and descended ramps. That the knee with adaptive control was ultimately selected by all users who experienced the studied knee technologies suggests that walking speed or perceived function were important factors in their choice or that outcomes that showed nonsignificant improvements (e.g., fast walking speeds, stair ascent/descent, or step activity) may be perceptible, wrote the study’s authors.
Active knee control, as found in the Össur Power Knee II, significantly limited users’ laboratory-based mobility and overall daily activity. Users’ long-distance walking ability and perceived mobility, function, and health were comparable between knees with active and passive control. However, generally poor outcomes and high attrition of subjects in the active knee condition suggest that active knee control, as it is implemented in the Power Knee II, may not be ideal for middle-age or older people with a transfemoral amputation.
The study was published in the Journal of Rehabilitation Research & Development (JRRD) Volume 52 Number 6, 2015.
