The purpose of this study was to investigate the energy cost of walking after total ankle arthroplasty (TAA), and to investigate if possible differences could be attributed to changes in external mechanical work required for the step-to-step transition.

Eleven patients, 6 months to 4 years after successful unilateral TAA, and 11 healthy controls walked on a treadmill at a self-selected speed (SWS) and a fixed walking speed (FWS, 1.25 m/s). Ground reaction forces and oxygen uptake were measured. External mechanical work was analyzed using the double inverted pendulum model.

At SWS, velocity in the TAA group was reduced (v=1.29 vs 1.42 m/s, p=0.05) but metabolic energy cost was not different (E=2.50 vs 2.24 J/kg/m, p=0.32). At FWS, metabolic energy cost in the TAA patients was significantly higher (E=2.58 vs 1.96 J/kg/m, p=0.003). The difference in metabolic energy cost at FWS coincided with an increased negative work in the leading leg and reduced positive work in the trailing leg with TAA during double support. Although this indicates that the mechanical work for the step-to-step transition increases, the total external mechanical work over a complete stride was not different between the TAA and the control group.

TAA patients walk at a higher metabolic energy cost. This cannot be explained by differences in external mechanical work. Other factors, such as changes in muscle function, should be taken into account.