Plastic Surgery Research Council
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Presenter: Edward P Washabaugh IV, Student
Co-Authors: Langhals NB; Kung TA; Moon JD; Cederna PS; Urbanchek MG
University of Michigan

Background: Myoelectric robotic arms can provide reasonable functional recovery for an upper extremity amputee. Unfortunately, there is no reliable, stable way to provide motor control of high fidelity neuroprosthetic devices. A permanent alternative is the regenerative peripheral nerve interface (RPNI). RPNIs are surgically transferred autogenous muscle which is neurotized with residual native nerve endings. An electrode is implanted in each RPNI. Our purpose is to increase the number of functional RPNIs reinnervated by one peripheral nerve.

Methods: Rats (n=6) were assigned to surgical groups: 1 RPNI, 2 RPNIs, or 3 RPNIs (Fig 1). The RPNI groups had unilateral peroneal nerve (PN) transected at the knee. Then the ipsilateral soleus muscle was grafted into the upper thigh. For the 1 RPNI group, the entire distal end of the peroneal nerve was implanted into the soleus muscle. For the 2 RPNI and 3 RPNI groups, either 1 or 2 additional donor soleus muscles were implanted in the thigh. The PN was split with each fascicle neurotizing one RPNI. Additionally each RPNI had a fine wire electrode implanted within the grafted RPNI muscle. Three months postoperatively, RPNI-evoked electromyography and force were measured.

Results: All RPNIs were reinnervated and recovered contractile function. Recovered CMAP areas for the 1RPNI, 2RPNI, and 3RPNI groups were 25%, 25%, and 10% when compared with normal soleus muscle. Active contractility was isolated to specific RPNI when the nerve section innervating the RPNI was stimulated indicating RPNI independent function. The specific forces for each group were 50% lower than normal muscle indicating the RPNIs contained increased non-contractile material (Fig 2, Table 1).

Conclusions: Peripheral nerve signal amplification of these magnitudes verifies that we can successfully reinnervate multiple RPNIs from a single nerve. By separating these fascicles, we have validated our model of multiple independent RPNIs within a small region of the body for use in providing multiple movement control in replacement prostheses.
This work was sponsored by DARPA Contract No. N66001-11-C-4190.

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