Fascicular injury is rare following needle transfixion: a study on median and ulnar isolated human nerves.

Background: Needle trauma has been associated with peripheral nerve injury and neurological dysfunction. However, inadvertent needle puncture is frequent while postblock 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 fresh human cadavers. Four different needles were used for the transfixing punctures: A 30° beveled (22G) nerve block needle, and 15° beveled (22G, 25G and 27G) Quincke spinal block needles. 10 transfixing punctures were made with each needle type on each nerve (40 punctures per nerve). Samples were then immersed in 5% formaldehyde solution for 30 days. Perpendicular cross-sections of the punctured segments were obtained. Samples were embedded in paraffin and analyzed under light microscopy with H&E staining. On each slice, the following variables were obtained: ratio of fascicular/epineurial tissue, the number of fascicles per nerve and the number of injured fascicles.

Results: A total of 400 punctures were made (200 median and 200 ulnar) and 144 histological nerve sections analyzed (74 median and 70 ulnar). The median number of fascicles per section was 16 (range 7-23) and 17 (range 8-27) with a fascicular/epineural tissue ratio of 45% (range 35%-52%) and 44% (range 39%-54%) for median and ulnar, respectively. Three fascicular injuries were identified: one in ulnar and two in median. All injuries were caused by a 15° beveled needle, the ulnar with a 22G and the median with a 22G and a 27G.

Conclusions: Fascicular injury is rare following needle transfixion. Needle injury alone is unlikely to explain postblock neurological dysfunction.