K3 Promoter™ Prosthetic Foot Reduces the Metabolic Cost of Walking for Unilateral Transtibial Amputees

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Abstract
Though the designs of lower-leg prostheses have changed over time, none have substantially improved metabolic energy demand, preferred walking speed, or gait symmetry. If elastic energy can be more effectively stored and returned from a prosthetic foot that has a spring stiffness similar to that of a biological human ankle, persons with transtibial amputations may be able to experience biomimetic gait patterns and a more economical metabolic cost during walking. We compared the metabolic rates, kinematics, and kinetics of four unilateral transtibial amputees while they walked at 0.75–1.50 m/s using their own elastic storage and return prosthesis and using a recently developed prosthetic foot (K3 Promoter™). The K3 Promoter is novel, because it has a nonlinear loading response that qualitatively emulates the loading response of a biological ankle, and it has midfoot and metatarsal-phalangeal joints with biological functional ranges of motion. We found that amputees' average net rates of oxygen consumption were 4%–12% lower, varying with speed of locomotion, while wearing the K3 Promoter compared with wearing their own conventional elastic storage and return prosthesis. However, the K3 Promoter did not dramatically improve gait symmetry, thus the effects of symmetry on metabolic cost deserve further attention. The K3 Promoter could considerably improve walking endurance for amputees by reducing fatigue and may be particularly beneficial to amputees with limited cardiovascular capacity.

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