Nerve Action Potential Recording for Nerve Lesions

Experiments with lesioned primate nerves suggested positive nerve action potential (NAP) recordings could antedate clinical as well as electromyographic recovery by weeks to months. Negative recordings after the elapse of several months correlated with less favorable regeneration through lesions in continuity. Axonal counts of resected nerves suggested that a regenerative NAP depended on the presence of 4000 to 5000 nerve fibers 5 microns or greater in diameter.

Similar operative recordings using tripolar electrodes for stimulation and bipolar electrodes for recording, and a variety of oscilloscopic recording instruments have been completed on 1736 patients with 3393 injuries in continuity involving a variety of peripheral nerves and plexus elements. Where a NAP was recordable beyond the lesion in the early months post injury, recovery with neurolysis led to a grade 3 or better level by using the LSUHSC grading system in 94.7% of nerves or plexus elements (1285 of 1356). Inspection as well as differential fascicular recordings led to split repair in 62 nerves with recovery in 58. Almost all of the lesions resected because of absence of an NAP across the lesion (1975) were neurotemetic or Sunderland grade III or IV by histologic evaluation. Recovery from suture or graft repair in this category was 56% (1111 of 1975 to grade 3 or better).

Recordings in 950 entrapped nerves usually but not always confirmed preoperative electrodiagnostic studies. Recordings in 364 ulnar entrapments validated the diagnosis in 62 cases where preoperative conductive studies were normal and documented the olecranon notch as the site of maximal nerve involvement in 95% of cases. Operative recordings at the supraclavicular level in a series of 160 suspected thoracic outlet cases showed amplitude and velocity abnormalities at the level of spinal nerves T1 and C8 close to the spinal column and not more laterally between the first rib and clavicle.

Need for recording proximal to the lesion or from less involved nerve or elements, differentiation of NAPs from muscle action potentials and preganglionic from post ganglionic responses, as well as proper electrode positioning were stressed, as well as the basic neurophysiology from which the technique has been derived.