Background and Aims Needle trauma has been associated to peripheral nerve injury and neurological dysfunction. However, inadvertent needle puncture is not infrequent while post-block dysfunction is rare. We conducted a cadaveric study to evaluate the association between needle puncture and fascicular injury.

Methods Five median and five ulnar (isolated) nerves were obtained from unembalmed fresh human cadavers. 4 different needles were used for the punctures: A 22G nerve block needle (Stimuplex 360, 30 degrees beveled), and 22G, 25G and 27G spinal needles (Yale, 15 degrees beveled). 10 transfixing punctures were made with each needle type on each nerve (40 punctures per nerve). Needles were withdrawn and nerves fixed in 5% formalin for 72 hours. Perpendicular microtome sections of the punctured segments were obtained. Samples were embedded in paraffin and analyzed under microscope with hematoxylin-eosin staining. For each section, the following variables were obtained: ratio of fascicular/epineurial tissue, number of fascicles per nerve, number of injured fascicles.

Results A total of 400 transfixing punctures were made (200 in median and 200 in ulnar) and 144 histological nerve sections analyzed (74 median and 70 ulnar). Median nerves had 15 +/-3 fascicles and ulnar 17+/- 4. The ratio of fascicular/epineural tissue was 47 +/-14% in median and 43+/-6% in ulnar. Three fascicular injuries were found (1 in median, 2 in ulnar). All 3 injuries were caused by a 15 degree beveled needle (22G in median, 27G and 22G in ulnar).

Conclusions The risk of fascicular injury is low following a transfixing needle puncture.