Histological evaluation of fascicular damage following repeated sciatic nerve transfixion: an anatomical study

Background: Ultrasound guidance has improved the accuracy and safety of peripheral nerve blocks, yet intraneural and even intrafascicular needle placement remains possible. The true incidence of fascicular injury after direct nerve transfixion is uncertain due to limited histological data. This study aimed to determine the frequency of fascicular damage after needle transfixion of the sciatic nerve using a human anatomical model. Methods: A sciatic nerve segment was harvested from a fresh-frozen male cadaver without neurological disease. One hundred full-thickness transfixions were performed using a 22-gauge sharp needle, simulating accidental intraneural penetration. Each transfixion was replicated using a standardized technique. The nerve was fixed in formalin, sectioned every 5 mm, embedded in paraffin, and stained with hematoxylin and eosin for histological evaluation. The presence of fascicular injury or displacement was assessed microscopically. Descriptive statistics were used to summarize findings, and proportions with 95% confidence intervals were calculated using the Wald method. Results: All 100 needle trajectories were successfully identified histologically. Clear fascicular damage was observed in 30 of 100 transfixions, corresponding to an incidence of 30% (95% confidence interval, 21 to 39%). In four additional cases, the needle passed in close proximity to fascicles, causing their displacement without visible structural injury, yielding an incidence of 4% (95% confidence interval, 0.2 to 7.8%). In the remaining cases, the needle path did not involve any fascicles. Conclusions: One third of simulated sciatic nerve transfixions performed with a sharp needle resulted in direct fascicular injury, while a smaller proportion produced fascicular displacement without structural disruption. These findings suggest that fascicular penetration is more common than previously believed when sharp needles are used and highlight the potential for mechanical nerve injury during regional anesthesia procedures. The use of sharp needles for peripheral nerve blocks should be avoided, and further research should explore how needle design and tip geometry influence the likelihood of fascicular injury.