Authors of a study addressing how stumble conditions affected transfemoral prosthesis users concluded that introducing muscle strength or task-specific motor skill training and/or modifying assistive devices may improve stumble responses. Specifically, the researchers wrote, training or exoskeleton assistance could help facilitate sufficient thigh/knee flexion for elevating, and training or prosthesis assistance could provide support-limb counteracting torques to help with elevating and initiate and safely complete prosthetic swing.
Six unilateral transfemoral prosthesis users walked on a treadmill at 0.8 m/s while researchers targeted a series of obstacle perturbations to occur in early, mid, and late swing phase (less than 40 percent, 40-60 percent, and greater than 60 percent swing) on the prosthetic side and on the sound side. A 35 lb. obstacle was positioned on a ramp in front of the treadmill and held in place by an electromagnet; when cued from an onboard targeting algorithm, the electromagnet released the obstacle down the ramp and onto the treadmill belt. The number of steps prior to perturbation, limb stumble, and swing phase targeted were randomized.
Data from a previous stumble study with seven adults without amputations who underwent a similar process was used for comparison. Those participants experienced approximately 28 obstacle perturbations while walking at 1.1 m/s, and no participants fell. The latest study provided data about fall outcome, recovery strategy, and kinematics of each response to characterize recoveries versus falls and prosthesis user recoveries versus healthy adult recoveries. The researchers also considered factors including the prosthesis user’s age, prosthesis type, side tripped, and swing phase of perturbation.
Out of 26 stumbles, 15 resulted in falls with five of six transfemoral prosthesis users falling at least once. The two oldest participants fell after every stumble, and stumbles in mid swing resulted in the most falls; prosthesis type was not related to strategy/fall outcomes.
The researchers found that the prosthesis users who recovered used the elevating strategy in early swing, lowering strategy in late swing, and elevating or lowering/delayed lowering with hopping in mid swing, but they exhibited increased thigh abduction on their prosthetic side and increased trunk flexion relative to healthy controls.
Falls occurred if the tripped sound limb did not reach ample thigh/knee flexion to sufficiently clear the obstacle in the elevating step or if the prosthetic limb did not help provide a successful step response after the sound side elevating or lowering step.
The open-access study, “Factors leading to falls in transfemoral prosthesis users: A case series of sound-side stumble recovery responses,” was published in the Journal of NeuroEngineering and Rehabilitation.
