A Coronally-Clutching Ankle to Improve Amputee Balance on Coronally-Uneven and Unpredictable Terrain

Abstract

To improve amputee balance on coronally-uneven and unpredictable terrain, a coronally-clutching ankle (CCA) prosthesis was developed and tested using amputee participants. In its adapting mode, the CCA device enabled free coronal rotation of the prosthetic foot of up to ±15° from horizontal, and approximately 100 ms after heal strike, would cease further rotation. The CCA was tested on three healthy amputee participants that stood still on, and walked across, an instrumented disturbance device that was capable of producing unpredictable inversions and eversions of 15°. Participants’ balance during gait over the coronally-uneven and unpredictable terrain was evaluated using the range of coronal angular momentum. This metric exhibited no significant pairwise differences between participants’ as prescribed prosthesis and the CCA in its adapting mode, suggesting the CCA did not improve gait balance on coronally-uneven and unpredictable terrain. Lateral sway of participant’s center of pressure measured their balance as they stood still on the coronally-uneven terrain. Again, no significant pairwise differences were observed between prosthesis conditions; however, it appeared the CCA in its adapting mode may have slightly improved participant balance, especially in inversion. During walking trials, the CCA in adapting mode was able to match the coronal angle of the foot to that of the terrain. However, evaluation of the moment about the CCA pivot revealed that its distance from the bottom of the prosthetic foot prevented the CCA from reducing the disturbance moment produced when amputees stepped on the coronally-uneven and unpredictable terrain. Furthermore, when the CCA was adapting to coronally-uneven and unpredictable terrain, large oscillations of the disturbed limb’s hip moment were observed, suggesting participants required additional recovery strategies to compensate for the CCA’s adaption. Thus, while the CCA in this study was able to adapt the coronal foot angle to coronally-uneven and unpredictable terrain, a clear benefit to gait balance was not observed. A possible benefit to standing balance was observed, but was not statistically significant. Future iterations of the CCA device will incorporate the learnings of this study to improve the balance outcomes of amputees on coronally-uneven and unpredictable terrain.