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C7 NERVE ROOT SENSORY MAPPING: A FUNCTIONAL MRI INVESTIGATION
Presenter: Jacques A Machol IV, MD
Co-Authors: Li R; Hettinger PC; Flugstad NA; Yan JG; Matloub HS; Hyde JS
Medical College of Wisconsin

Introduction: In the case of severe brachial plexus avulsion injury, the C7 nerve root is identified as a possible donor for nerve transfer. This study aims to elucidate the linear relationship of each major upper limb nerve (ulnar, median, radial, and musculocutaneous) to the C7 cortical map by means of sensory stimulation. We hypothesize that if the linear makeup is less than the 20% of each nerve, then this will help to expound why C7 is a suitable donor for brachial plexus injury treatment.

Methods: An operating microscope was utilized to isolate the brachial plexus and the C7 nerve root in male Sprague-Dawley rats (150-200 g). A 125 m diameter stainless steel bipolar electrode was placed circumferentially around the right C7 nerve root. Functional magnetic resonance imaging (fMRI) was performed while mild electrical C7 stimulation at 10 Hz frequency was applied. This was compared for voxel overlap within the S1FL cortex of previously mapped data for each major upper extremity peripheral nerve sensory region.

Results: The C7 nerve root sensory cortical representation area only occupies a very small amount of total activated area in all nerve maps: less than 1% in the musculocutaneous, 6% in the ulnar, 16% in the radial, and 19% in the median nerve (P<0.005 for each).

Conclusions: As hypothesized, the overlap is always under 20% for each major nerve. This is exclusively within the ability of each major nerve to compensate and is likely a facet of why C7 is a suitable donor for brachial plexus injury repair.


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