Use of a powered ankle-foot prosthesis reduces the metabolic cost of uphill walking and improves leg work symmetry in people with transtibial amputations

Abstract

People with transtibial amputations (TTAs) who use a powered ankle-foot prosthesis have equivalent metabolic costs and step-to-step transition work for level-ground walking over a range of speeds compared to non-amputees. The effects of using a powered compared to passive-elastic prosthesis for sloped walking are unknown. We sought to understand how the use of passive-elastic compared to powered ankle-foot prostheses affect metabolic cost and step-to-step transition work during sloped walking. Ten people (six M, four F) with TTAs walked 1.25 m s-1 at 0°, ±3°, ±6° and ±9° using their own passive-elastic prosthesis and the BiOM powered ankle-foot prosthesis, while we measured metabolic rates, kinematics and kinetics. We calculated net metabolic power, individual leg step-to-step transition work and individual leg net work symmetry. The net metabolic power was 5% lower during walking on +3° and +6° uphill slopes when subjects used the BiOM compared to their passive-elastic prosthesis (p < 0.05). The use of the BiOM compared to a passive-elastic prosthesis did not affect individual leg step-to-step transition work (p > 0.05), but did improve individual leg net work symmetry on +6° and +9° uphill slopes (p < 0.01). People with TTAs who use a powered ankle-foot prosthesis have the potential to reduce metabolic costs and increase symmetry during walking on uphill slopes.

Keywords: amputee; gait; leg work; prosthetic; slopes; step-to-step transition.

Conflict of interest statement

We declare we have no competing interests.

© 2018 The Author(s).

Figures

Figure 1.

‘Malleolus’ marker placement on the encoder/centre of rotation for the BiOM powered prosthesis. (Online version in colour.)

Figure 2.

Results of iteratively tuning the BiOM for subjects walking at 1.25 m s−1 compared to non-amputees (black) (a) ankle range of motion, (b) peak ankle moment, (c) peak ankle power and (d) net ankle work (mean ± s.e.). BiOM prosthetic ankle data collected at the end of the tuning day (white) and on the final day of the protocol (grey). Data collected on day 6 were used for analyses.

Figure 3.

Net metabolic power (mean ± s.e.) of subjects with a TTA walking 1.25 m s−1 on slopes of −9° to +9° with the BiOM powered ankle–foot (white) and passive-elastic ESAR (grey) prostheses. *Significant difference between BiOM and ESAR.

Figure 4.

Positive affected leg (AL) trailing step-to-step transition work (mean ± s.e., J kg−1, top) and negative unaffected leg (UL) step-to-step transition work (±s.e., J kg−1, top) for subjects with a TTA walking 1.25 m s−1 on slopes of −9° to +9° with the BiOM powered ankle–foot (white) and passive-elastic ESAR (grey) ankle–foot prostheses. There were no significant differences between prostheses.

Figure 5.

Net leg work (positive work + negative work = net work) symmetry (AL/UL) over an entire stride for subjects with a TTA walking 1.25 m s−1 on slopes of −9° to +9° with the BiOM powered ankle–foot (white) and passive-elastic ESAR (grey) ankle–foot prostheses. 1.0 indicates perfect symmetry. *Significant difference between BiOM and ESAR prostheses.