Transfemoral limb loss modestly increases the metabolic cost of optimal control simulations of walking

ABSTRACT

Unlike the case of transtibial limb loss, high-functioning military service members with transfemoral limb loss have a high metabolic cost of walking compared to able-bodied peers. In transtibial limb loss, computer simulations suggest that the maintenance of muscle strength between pre- and post-limb loss can maintain the pre-limb loss metabolic cost. Here we performed optimal control simulations of walking with and without transfemoral limb loss to determine if transfemoral limb loss per se increases the metabolic cost of walking. OpenSim Moco was used to generate optimal control simulations of walking in 15 virtual subjects that minimized the weighted sum of (i) deviations from average able-bodied gait mechanics and (ii) the gross metabolic cost of walking, pre-limb loss in models with two intact biological limbs, and post-limb loss with one of the limbs replaced by a transfemoral prosthesis. No other changes were made to the model. Metabolic cost post-limb loss increased by 0.7-9.3% (p < 0.01) depending on whether cost was scaled by total body mass or biological body mass and on whether the prosthetic knee was passive or non-passive. The post-limb loss model had numerous features that predisposed it to low metabolic cost. These results suggest that transfemoral limb loss per se increases the metabolic cost of walking, but that the large differences above able-bodied peers of ∼20-45% in most gait analysis experiments may be avoidable, even when minimizing deviations from able-bodied gait mechanics.