A Haptic Feedback System for Lower Limb Amputees Based on Gait Event Detection

Lower limb amputation has significant effects on a person’s quality of life and
ability to perform activities of daily living. Prescription of prosthetic device post
amputation aims to help restore some degrees of mobility function, however studies
have shown evidence of low balance confidence and higher risk of falling among
amputee community, especially those suffering from above knee amputation. While
advanced prostheses offer better control, they often lack a form of feedback that
delivers the awareness of the limb position to the prosthetic user while walking.
This research presents the development and evaluation of a wearable skinstretch haptic feedback system intended to deliver cues of two crucial gait events,
namely the Initial Contact (IC) and Toe-off (TO) to its wearer. The system comprises
a haptic module that applies lateral skin-stretch on the upper leg or the trunk,
corresponding to the gait event detection module based on Inertial Measurement Unit
(IMU) attached at the shank. The design and development iterations of the haptic
module is presented, and characterization of the feedback parameters is discussed.
The validation of the gait event detection module is carried out and finally the
integration of the haptic feedback system is described.
Experimental work with healthy subjects and an amputee indicated good
perceptibility of the feedback during static and dynamic (walking) condition, although
higher magnitude of stretch was required to perceive the feedback during dynamic
condition. User response time during dynamic activity showed that the haptic
feedback system is suitable for delivering cues of IC and TO within the duration of
the stance phase. In addition, feedback delivered in discernible patterns can be learned
and adapted by the subjects.
Finally, a case study was carried out with an above-knee amputee to assess the
effects of the haptic feedback on spatio-temporal gait parameters and on the vertical
ground reaction force during treadmill and overground walking.
The research presented in this report introduces a novel design of a haptic
feedback device. As such, the outcome includes a well-controlled skin-stretch effect
which contributes to the research by investigating skin-stretch feedback for conveying
discrete event information rather than conveying direction information as presented in other studies. In addition, it is found that stretch magnitude as small as 3 mm could
be perceived in short duration of 150 ms during dynamic condition, making it a
suitable alternative to other widely investigated haptic modality such as vibration for
ambulatory feedback application. With continuous training, the haptic feedback
system could possibly benefit lower limb amputees by creating awareness of the limb
placement during ambulation, potentially reducing visual dependency and increasing
walking confidence.