Sensory Feedback for Lower Extremity Prostheses Incorporating Targeted Muscle Reinnervation (TMR)
Abstract
Body armor and improvements in battlefield medicine are saving lives in current conflicts, but rates of major limb amputation have increased. Nearly 1500 of the 1715 Iraq and Afghanistan US military battle-injury amputations as of December 3, 2012 have been major limb amputations. Overall in the United States there are about 1.7 million people with limb amputations, and increasing. Many significant theaters of operations for the armed services are now urban, so Service members returning to active duty with amputations would greatly benefit from an improved ability to navigate over stairs and steps. Stair ambulation is an activity of daily living for civilians and Veteran amputees as well. The purpose of this research is to improve the confidence and performance of below-knee amputees in stair descent. We will deliver feedback of prosthetic foot placement with respect to the edge of the stair and explore how this feedback should be delivered to subjects having undergone Targeted Reinnervation (TR) surgery. TR is an innovative surgical procedure for redirecting nerves leading to the amputated extremity to target remaining muscles. TR nerve transfers promote motor reinnervation, which has proven useful for controlling myoelectric prostheses. An unintended and potentially equally important finding is that there can be profound sensory reinnervation as well -- when the amputee is touched at the site of the TR, he or she feels the sensation in the missing limb. Until now, however, research on the sensory reinnervation of TR recipients has been primarily limited to upper extremity. It has been shown that feedback on the skin of the TR site can improve function. For example, a subject receiving feedback of prosthetic fingertip forces might report that the feedback naturally feels as if it is coming from the missing fingertips. We have an analogous opportunity then to address the sensory deficits caused by lower limb loss for challenging ambulation tasks requiring precise movement, such as stair descent. The user of a prosthetic foot, even the new microprocessor-controlled active ones, has extremely limited access to ankle dorsiflexion. When below-knee amputees in stair descent place their prosthetic foot with little overhang over the stair, they exhibit a markedly asymmetric movement pattern characterized by increased load on the contralateral leg joints. One strategy for overcoming this restricted range of motion is to place the prosthetic foot with greater overhang off the lip of the stair, using vision to ensure proper placement. The resultant moment on the prosthetic ankle is reduced, and the body pivots over the stair lip. The consequences of foot placement are great, but cannot be felt until the step has already begun. We propose to develop a vibrotactile sensory replacement system for foot placement on a stair and to lay the groundwork for adapting the system for the subject-specific characteristics of TR amputees. Specific Aim 1: Systematically map and characterize the sensory capabilities of TR sites under vibrotactile stimulation. The sensory consequences of lower extremity TR have not yet been shown in the context of a vibrotactile feedback array. We will map the extent and acuity of sensory reinnervation as it has previously been done for upper extremity, using monofilaments to touch the skin, but also by using vibrating tactors, as it would actually be felt when using a sensory-feedback prosthetic device. We will compare the discriminability of the stimulation with amputees not having TR. Specific Aim 2: Determine the effects of vibrotactile cues of foot placement on stair descent of below knee amputees. We will compare self-selected speed and foot placement during stair descent using an integrated motion capture stair machine. The system will allow the user to descend at any rate without exiting the stair-workspace. There has been only limited study of stair descent in amputees,
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 29, 2016
- Source ID
- W81XWH1510417
Entities
People
- Eric Rombokas
Organizations
- Seattle Institute for Biomedical and Clinical Research
- United States Army