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Novel Methodology For Systematic Sensory Characterization And Stimulus Testing After Major Limb Loss
David A. Boe, BS1, Dennis S. Kao, MD2, Eric Rombokas, PhD1, Yusha Liu, MD, PhD1.
1University of Washington, Seattle, WA, USA, 2Cleveland Clinic, Cleveland, OH, USA.

PURPOSE: Sensory referral is commonly experienced by patients after amputation, in which touches to the residual limb are perceived as originating from the phantom limb. This phenomenon offers a compelling interface for noninvasive delivery of sensory feedback in prosthetic limbs. However, a more comprehensive understanding of the complexities of the sensory experience is necessary, especially with the rising popularity of surgical techniques such as targeted muscle reinnervation (TMR) and regenerative peripheral nerve interfaces (RPNI). We hypothesize that in TMR and RPNI, repurposing and providing transected nerves with muscle targets for reinnervation may alter or induce patterns of referred sensation.
METHODS: To study this, we have developed a novel methodology for detailed sensory characterization of the residual limb, compatible for both upper and lower extremity amputation. We designed a computer program for mapping sensory referral, in which participants interact with a virtual representation of their phantom limb (Fig 1). With a touchscreen laptop, participants can zoom and rotate to see the entire limb. Light touch, deep pressure, and vibratory stimuli are presented to the residual limb, and participants tap on the virtual limb to mark the location of the perceived sensation.


RESULTS: Our software interface is intuitive for participants to use and is designed to provide a standardized testing methodology, such that any researcher may quickly and confidently perform rigorous, repeatable sensory characterization of a limb. It also minimizes experimenter bias by eliminating ambiguity in verbal responses; participants tap directly on the virtual limb where the feeling appears to originate without needing to verbally describe that anatomical location. The data points on the virtual limb can then be correlated with the tested points on the residual limb to generate a map of referred sensation.
CONCLUSION: Providing an egocentric virtual body for sensory testing enables participants to indicate with high accuracy where a stimulus is perceived on their phantom limb. With our innovative tool, we can screen for individuals with sensory referral and generate complete sensory referral mappings of the residual limb. Aspects of sensory capabilities can be compared across individuals and groups, including surface area of referring skin and rate of referral to peripheral nerve distributions or phantom limb anatomy. Our systematic methodology will facilitate unbiased explorations of sensory referral after amputation, especially after TMR and RPNI surgery.


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