American Society for Peripheral Nerve

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Features of Vagus Nerve Innervation to Motor Nerves Utilizing Helicoid End-to-Side Neurorrhaphy in Rats
David Rivedal, MD1; Ji-Geng Yan, MD, PhD2; Feng-Yi Shen, MD3; Juan Figueroa, MD4; Hani Matloub, MD5; Lin-Ling Zhang, MD5; Robert Havlik, MD5
1Medical College of Wisconsin, Wauwatosa, WI, 2Department of Plastic Surgery, Medical College of Wisconsin, Wauwatosa, WI, 3Froedtert Health - Community Memorial Hospital, Menomonee Falls, WI, 4Medical College of Wisconsin, Milwaukee, WI, 5Plastic Surgery, Medical College of Wisconsin, Milwaukee, WI

Total avulsion brachial plexus nerve injury (TABPI) is debilitating. Lack of donor nerves makes TABPI extremely difficult to repair. Traditionally, the semi-autonomic phrenic nerve (PN) can be utilized as a donor and coapted end-to-end (EE) to a peripheral recipient nerve; however dissection can be tedious and cause diaphragm compromise. The autonomic vagus nerve (VN) has a wide diameter and is easy to dissect. This study examines whether VN can be converted to a somatic motor nerve by helicoid end-to-side neurorrhaphy (HS) and to validate this technique as reliable and effective for nerve transfer.

Sprague Dawley (SD) male rats were used in this Institutional Animal Care and Use Committee approved study. The rats were divided into four groups: HS-VN - saphenous nerve (SN) was grafted helicoidally around VN, another end was coapted to the transected musculocutaneous nerve (McN); HS-PN - SN was grafted helicoidally between PN and McN; EE-PN - SN was grafted EE between transected PN and McN; control - McN was transected and ligated. Three months post-surgery EMG and biceps force testing was performed along with histologic studies. ANOVA and two-sample t-tests were used for statistical analysis.

Twenty-four SD rats were evenly divided into four groups. Mean elbow flexion angle and mean recovery rate in order of size was HS-VN>HS-PN>EE-PN>control (110, 85, 45, 0 degrees; 90%, 71%, 38%, 0%). Compared to each group, HS-VN had statistically significant increased recovery. Rhythmic elbow flexion with regular breaths was seen in HS-PN and EE-PN groups, however this co-contraction was not seen in HS-VN. Mean compound muscle action potentials (CMAP) and CMAP recovery in order of size was HS-VN>HS-PN>EE-PN>control (19, 16, 12, 0 mV; 79%, 67%, 50%, 9%). Mean contractile forces in order of size was HS-VN>HS-PN>EE-PN>control (227, 220, 252, 5 grams). HS-VN/HS-PN contractile force was greater than EE-PN (p=0.0009). HS-VN mean nerve fiber numbers of VN proximal and distal to HS was 2237 and 2150, which were not statistically significant. Regenerated myelinated nerve fibers distal to SN-McN coaptation site in HS-VN, HS-PN, EE-PN and control groups were 1530, 1649, 1391, and 0.

This study demonstrated VN innervated somatic muscle after HS leads to at least equivalent muscle contraction compared to traditional EE nerve transfer. Compared to PN, there was no muscle co-contraction with biceps flexion. Finally, VN is a safe and reliable donor nerve in the rat model with future potential in humans.

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