Electrodiagnostic values through the thoracic outlet using C8 root needle studies, F-waves, and cervical somatosensory evoked potentials.

Mid-humerus cadaver determinations of ulnar F-wave, C7 spinal somatosensory evoked potential (SEP), and modified C8 root stimulation (RS) were performed bilaterally on 20 normal subjects to standardize technique and obtain normal values for the segment from mid-humerus to cervical spine. Our cadaver study shows that the best position for upper extremity measurement of mid-humerus-cervical spine distance is at 60 degrees of shoulder abduction, 45 degrees of internal rotation, and at the distance of 35cm, measured by caliper. Using this position and distance the following normal values were obtained: 1) Mid-humerus F-wave minimal, maximal, and mean latencies, and minimal nerve conduction velocity (NCV) were 21.8 +/- 1.2msec, 22.3 +/- 1.2msec, 22.3 +/- 1.1msec, and 59.7 +/- 2.4m/sec, respectively. Latency difference between minimal and maximal F-wave was 1.4 +/- 0.4msec. 2) Cervical spine SEP was 5.1 +/- 0.4msec, with left to right difference of less than 0.9msec. 3) C8 RS and mid-humerus ulnar nerve (UN) pick-up latency and NCV were 4.9 +/- 0.2msec and 71.4 +/- 2.2m/sec, whereas C8 root pick-up and mid-humerus UN stimulation latency and NCV were 5.2 +/- 0.4msec and 66.9 +/- 5.2m/sec, respectively. To evaluate proximal nerve conductivity through the thoracic outlet, the sequential use of the three modified techniques for 35cm mid-humerus-cervical spine distance is recommended.