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PURPOSE: Our ultimate goal is the development of a regenerative peripheral nerve interface (RPNI) for closed loop neural control of prostheses. This interface integrates amputee's residual peripheral nerves with transferred skeletal muscle. The purposes of this study are; with respect to controls: a) to compare the electrical properties of RPNI at 1 and 3 months after implantation and b) to compare the resultant RPNI neurotization and muscle function at 3 months.
METHODS: Rats (n = 29) were divided into three groups: sham operated (Sham), free muscle transfer with no nerve innervation (MT), and muscle transfer with residual nerve implantation (RPNI). During sham surgeries, the right leg was dissected to expose the soleus muscle and then surgically closed. For both MT and RPNI groups the right soleus muscle was transferred between interstitial tissues of the left thigh, parallel with the femur. In the RPNI group the left peroneal nerve was divided and the proximal end sutured within the transferred muscle. After either 1 or 3months of implantation the transferred muscles were tested using both nerve conduction studies and muscle force testing. Histology was performed on nerves and muscles.
RESULTS: All surgical group muscles were viable at 1 and 3 months post-surgery; all data were analyzed. The RPNI at 3 months showed greatly improved functions over the 1 month RPNI values. Compound muscle action potential (CMAP) amplitude improved by 200%, CMAP area improved by 370%, and stimulus threshold voltage was beneficially decreased by 80% (Tables 1 & 2). RPNI values at 1 month showed distinctly less function when compared with Sham muscles but better function than the MT not neurotized controls.. But by 3 months of recovery, RPNI improved function was no longer different from Sham muscles for CMAP amplitude, CMAP area, stimulus threshold, or maximal muscle force. RPNI neuromuscular junction density was 317% increase over Sham muscles.. The negative control MT muscles showed significantly worse function than the Sham muscles at 3 month recovery for nerve conduction measurements.
CONCLUSION:
That functional neurotization follows nerve implantation into transferred muscle is the basis for RPNI use as a neural interface. We measured recovery of conduction and contractile functions within RPNI which compared favorably with Sham operated rats. These data confirm that neurotization occurs within the RPNI, allowing recovery of muscle responsivity to moderate stimulation and muscle contractile forces similar to sham muscle. These finding support RPNI use as an interface to neuroelectric prostheses.
The views expressed in this work are those of the authors and do not necessarily reflect official Army policy. This work was supported by the Department of Defense Multidisciplinary University Research Initiative (MURI) program administered by the Army Research Office under grant W911NF0610218.