Research Article: Kinematic and biomimetic assessment of a hydraulic ankle/foot in level ground and camber walking

Date Published: July 13, 2017

Publisher: Public Library of Science

Author(s): Xuefei Bai, David Ewins, Andrew D. Crocombe, Wei Xu, Steven Allen Gard.


Improved walking comfort has been linked with better bio-mimicking of the prosthetic ankle. This study investigated if a hydraulic ankle/foot can provide enough motion in both the sagittal and frontal planes during level and camber walking and if the hydraulic ankle/foot better mimics the biological ankle moment pattern compared with a fixed ankle/foot device. Five active male unilateral trans-femoral amputees performed level ground walking at normal and fast speeds and 2.5° camber walking in both directions using their own prostheses fitted with an “Echelon” hydraulic ankle/foot and an “Esprit” fixed ankle/foot. Ankle angles and the Trend Symmetry Index of the ankle moments were compared between prostheses and walking conditions. Significant differences between prostheses were found in the stance plantarflexion and dorsiflexion peaks with a greater range of motion being reached with the Echelon foot. The Echelon foot also showed significantly improved bio-mimicry of the ankle resistance moment in all walking conditions, either compared with the intact side of the same subject or with the “normal” mean curve from non-amputees. During camber walking, both types of ankle/foot devices showed similar changes in the frontal plane ankle angles. Results from a questionnaire showed the subjects were more satisfied with Echelon foot.

Partial Text

Gait analysis is commonly used in the assessment of different prosthetic components to support the design, optimisation and selection of prostheses. Recently, there has been a series of gait studies on the functional performance of a clinically available ankle-foot hydraulic prosthetic device [1–5]. The hydraulic ankle-foot device is a passive single axis articulating design that allows custom control of the resisting moment. The gait from amputees with a hydraulic prosthetic ankle was compared with that using a fixed device and it was found that the hydraulic ankle/foot enabled decreased residual limb internal stresses, increased subjects’ self-selected walking speed, smoother and more rapid progression of prosthetic side plantar centre of pressure, and increased hip and knee joint power in both limbs [1–4].

One subject (subject TF4) fell during a trial of level ground normal speed walking with the first fitted prosthetic ankle/foot. The subject was not injured but for safety consideration, he was not asked to perform fast speed walking with either type of prosthetic ankle/foot. Another subject (subject TF2) had difficulties in getting clean single foot contacts with both force plates due to the large stride width in all tested walking conditions. Although the subject could deliberately reduce stride width to enable clean single foot contacts on both sides, as a “common” and “comfortable” walking condition was expected, we focused on clean single foot contacts from the prosthetic side only. Therefore the symmetry TSI of subject TF2 has not been calculated.

The primary aim of this research was to assess the kinematic and kinetic performance of a hydraulic prosthetic ankle/foot on level and camber walking conditions compared with a fixed prosthetic ankle/foot. This was carried out in two ways. Firstly, the kinematic performance in the sagittal was investigated on level ground walking at two speeds and on camber surfaces at normal speed. The second approach was to investigate if the hydraulic prosthetic ankle/foot device could provide better bio-mimicry of the resistance moment pattern compared with a fixed prosthetic device using symmetry and normalcy TSI as assessment tools. The secondary aim of this study was to assess the inversion/eversion movement of both types of prosthetic ankle/foot.

In conclusion, in all walking conditions (level ground normal speed walking, level ground fast speed walking, and camber walking from two directions), the hydraulic ankle/foot (Echelon) provides an increased range of motion in both plantarflexion and dorsiflexion during stance and better bio-mimicking of the ankle moment pattern than the fixed ankle design (Esprit). The inversion/eversion angle indicated that both types of the prosthetic ankles/feet allow adaption to a 2.5° camber from either direction. The questionnaire results suggest subjects are more satisfied with the hydraulic ankle/foot. Overall, bearing in mind the limitations outlined above, it is suggested that for active TFAs, the hydraulic ankle/foot enables an improved walking experience and comfort.




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