American Society for Peripheral Nerve

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Neuroma Formation after Soleus Grafting in a Peripheral Nerve Interface
Benjamin Wei, MD; Ziya Baghmanli; Kristoffer Sugg; Paul S. Cederna; Melanie G. Urbanchek
University of Michigan, Ann Arbor, MI, USA

Objective: Our goal is to develop a regenerative peripheral nerve interface (RPNI) for neural control of an artificial limb. Our RPNI uses the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), to reduce impedance and limit biofouling. Neuromas often accompany nerve lesions; they increase pain sensitivity and can cause signal interference. von Frey evaluations are used to evaluate sensitivity threshold. More sensitivity may imply more pain due to neuroma formation within the RPNI. Muscle can be used as an end organ for regenerating nerves. Our hypotheses are that a) tactile sensitivity is unaffected by the presence of PEDOT, and b) embedding divided nerves into free soleus grafts reduces tactile sensitivity.

Methods: In a rat model, the peroneal nerve is divided, and the proximal stump is coapted to a scaffolding of small intestinal submucosa (SIS). Animals designed to evaluate PEDOT are given scaffolds electrochemically polymerized with PEDOT. The contralateral soleus muscle is transferred to the ipsilateral thigh for peroneal nerve embedding. The study groups are as follows: Sham, SIS alone, SIS with Soleus, SIS with PEDOT, and SIS with PEDOT and Soleus. Tactile sensation is evaluated with von Frey filament stimulation at the operative site at 3 and 6 months. Statistical significance was determined by Kruskal-Wallis analysis.

Results: All of the experimental groups were more sensitive than the Sham group (α<0.06), consistent with an intact nerve differing from a divided nerve (Fig 1). Adding Soleus, PEDOT, or a combination of the two to the SIS scaffolding did not result in measurable differences. The presence of PEDOT and soleus muscle interact in their effect on sensitivity (Fig 2). The effect of PEDOT on sensitivity depends on the presence of soleus muscle. At 3 months of recovery, the addition of soleus increases sensitivity. However at 6 months, the addition of soleus decreases sensitivity. Histology is underway.

Conclusions: PEDOT showed minimal differences in tactile sensitivity compared to SIS scaffolding alone. These data suggest that PEDOT alone has minimal effect on sensitivity (neuroma formation). Our results also indicate that the effect of neurotizing soleus muscle has interactions with the effects of PEDOT as well as postoperative recovery time.


Figure 1: Tactile Sensitivity at 3 and 6 Months. Lower bars indicate greater sensitivity. *Different than sham, α < 0.06.


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