A research team analyzed the stumble recovery response of six transfemoral prosthesis users and found four key deficits in commercially available prostheses. The researchers concluded that mechanical or mechatronic changes to prosthetic design could improve recovery and reduce the likelihood of a fall.
The participants were perturbed on their prosthetic limb at least three times while walking on a treadmill using obstacle perturbations in early, mid-, and late swing. Kinematic data was collected to characterize the response, while fall rate and key kinematic recovery metrics were used to assess the quality of recovery and highlight functional deficits in current prostheses.
Across all participants, 13 of the 24 trials (54 percent) resulted in a fall (defined as greater than 50 percent body-weight support) with all but one participant (83 percent) falling at least once and two participants (33 percent) falling every time. In contrast, in a previous study of seven young, unimpaired, nonprosthesis users using the same experimental apparatus, no falls occurred across 190 trials.
For the prosthesis users, early swing had the highest rate of falling at 64 percent, followed by midswing at 57 percent, and late swing at 33 percent. The trend in falls was mirrored by the kinematic recovery metrics (peak trunk angle, peak trunk angular velocity, forward reach of the perturbed limb, and knee angle at ground contact). In early swing, all four metrics were deficient compared to nonprosthesis user controls. In midswing, all but trunk angular velocity were deficient. In late swing only forward reach was deficient.
Based on the stumble recovery responses, the researchers identified four potential deficiencies in the users’ prostheses: insufficient resistance to stance knee flexion upon ground contact; insufficient swing extension after a perturbation; difficulty initiating swing flexion following a perturbation; and excessive impedance against swing flexion in early swing preventing the potential utilization of the elevating strategy.
The open-access study, “Factors leading to falls in transfemoral prosthesis users: a case series of prosthesis-side stumble recovery responses,” was published in Journal of NeuroEngineering and Rehabilitation.
