Metabolic cost and mechanical work for the step-to-step transition in walking after successful total ankle arthroplasty

Abstract

The aim of this study was to investigate whether impaired ankle function after total ankle arthroplasty (TAA) affects the mechanical work during step-to-step transition and the metabolic cost of walking. Respiratory and force plate data were recorded in 11 patients and 11 healthy controls while they walked barefoot at a fixed walking speed (FWS, 1.25 m/s) and at their self-selected speed (SWS). At FWS metabolic cost of transport was 28% higher for the TAA group, but at SWS there was no significant increase. During the stepto-step transition, positive mechanical work generated by the trailing TAA leg was lower and negative mechanical work in the leading intact leg was larger. Despite the increase in mechanical work dissipation during double support, no significant differences in total mechanical work were found over a complete stride. This might be a result of methodological limitations of calculating mechanical work. Nevertheless, mechanical work dissipated during the step-to-step transition at FWS correlated significantly with metabolic cost of transport: r = .540. It was concluded that patients after successful TAA still experienced an impaired lower leg function, which contributed to an increase in mechanical energy dissipation during the step-to-step transition, and to an increase in the metabolic demand of walking.

Mechanical and energetic consequences of reduced ankle plantarflexion in human walking

“…3). But positive COM work over a stride appears not to capture the increased work demands resulting from reduced push-off (Doets et al, 2009), which appear to be met by the knee and hip (Fig. 7).…”

“…Its importance is illustrated by cases of impaired or reduced push-off, which generally require considerably more metabolic energy expenditure to walk at the same speed (Doets et al, 2009;van Engelen et al, 2010;Waters and Mulroy, 1999). If walking were only a matter of supplying a requisite amount of forward propulsion, then other joints might be expected to supply a greater proportion of the mechanical work to offset reduced push-off work, and not necessarily at higher metabolic cost.…”

“…For example, the peak can be reduced by more than half in patients with multiple sclerosis, those recovering from stroke (Bregman et al, 2011) and individuals with ankle arthrodesis or arthroplasty (Singer et al, 2013). The energetic penalty varies considerably with severity and condition, but typically entails an increase of 30% or more in net metabolic power (subtracting the cost of upright standing from gross power) to walk at the same speed (Doets et al, 2009;Torburn et al, 1995;Waters and Mulroy, 1999). There are surely many pathologyspecific contributors to that penalty, but here we examined fundamental costs that may potentially stem from altered mechanics during push-off.…”

“…In humans, the positive and negative work overlap during double support (Donelan et al, 2002a), but with earlier phasing for push-off (Adamczyk and Kuo, 2009). Indeed, in cases of total ankle arthroplasty, patients produce less push-off, resulting in greater collision losses and greater metabolic energy expenditure at a given speed (Doets et al, 2009). But one discrepancy is that overall positive work performed on the COM is not observed to increase (Doets et al, 2009), as would be expected from the imbalance between push-off and collision.…”

“…Indeed, in cases of total ankle arthroplasty, patients produce less push-off, resulting in greater collision losses and greater metabolic energy expenditure at a given speed (Doets et al, 2009). But one discrepancy is that overall positive work performed on the COM is not observed to increase (Doets et al, 2009), as would be expected from the imbalance between push-off and collision. The theory of step-to-step transitions would therefore appear to only partially explain the effects of reduced push-off.…”