In a study published in the Archives of Physical Medicine and Rehabilitation, researchers applied a user-modulated control strategy to improve control of a powered knee-ankle prosthesis during sit-to-stand and stand-to-sit movements.
Four men and three women who had unilateral transfemoral amputations and were capable of community ambulation participated in the within-subject comparison study. Each participant performed ten repetitions of sit-to-stand and stand-to-sit actions using a powered knee-ankle prosthesis and with their prescribed passive prosthesis in a randomized order. With the powered prosthesis, knee and ankle power generation were controlled as a function of weight transferred onto the prosthesis. The research team measured vertical ground reaction force limb asymmetry and durations of movement were compared statistically.
According to the study abstract, the results indicated that for sit-to-stand, peak vertical ground reaction forces were significantly less asymmetric using the powered prosthesis (19.3 percent [11.8 percent]) compared to using the prescribed prosthesis (57.9 percent [13.5 percent]), where positive asymmetry values represented greater force through the intact limb. For stand-to-sit, peak vertical ground reaction forces were also significantly less asymmetric using the powered prosthesis (28.06 percent [11.6 percent]) compared to using the prescribed prosthesis (48.2 percent [16.0 percent]). Duration of movement was not significantly different between devices (sit-to-stand: p=0.18; stand-to-sit: p=0.063).
The study, published online December 10, concludes that allowing individuals with transfemoral amputations more control over the timing and rate of knee and ankle power generation enabled them to stand and sit with their weight distributed more equally between limbs.