A Preliminary Study of the Effects of Active Recovery Reflexes on Stumble Recovery in a Swing-Assist Knee Prosthesis

This paper explores the effects of a swing phase stumble recovery controller in a swing-assist prosthesis. The prosthesis detects a stumble event and employs either a lowering recovery response - wherein the user's swing is truncated, and the leg is prepared for loading- or an elevating recovery response - wherein an amplified swing flexion is employed to step over the obstacle causing the perturbation. The controller described in this paper choses which of these responses to use based on the perturbation timing within the gait cycle, where stumble events which occur prior to an estimated 35 percent of the way through swing trigger an elevating response, and later stumbles trigger a lowering response. The potential efficacy of this approach was assessed in a preliminary study with two participants with transfemoral amputation; wherein each participant's walking was perturbed in early, mid, and late swing phase when wearing both their prescribed prosthesis and the swing-assist prosthesis prototype. When wearing the swing- assist device, 0 of the 13 perturbations resulted in falls, with none of the trials being classifiable as “near falls”. Conversely, when using their prescribed device, one participant had a fall rate of 3 out of 6 perturbations, with 1 of the 3 recoveries being classifiable as a “near fall”; the second participant had a fall rate of 0 of 3 trials, with 2 of the 3 recoveries being classifiable as “near falls”. For both participants, when recovery was achieved, it was accompanied by significantly longer periods of irregularity and asymmetry in gait when using their prescribed devices, as compared to the test device. These results suggest the possibility of substantial benefit provided by a low-power, reflex- based stumble recovery feature in knee prostheses.