Histological analysis after peripheral nerve puncture with pencil-point or Tuohy needletip.

Background: Continuous peripheral nerve blocks typically are performed with a "through-the-needle technique" and require needles with an inner diameter allowing catheter placement. In case of direct needle-nerve contact, the pencil-point needletip is currently considered less traumatic than are other needle configurations. In this study we determined whether nerve puncture with pencil-point needles is associated with fewer nerve injuries in comparison with Tuohy needles.
Methods: In 6 anesthetized pigs the brachial plexus were exposed bilaterally. Up to 8 nerves underwent nerve puncture with a pencil-point or a Tuohy needle. After 48 hours, the nerves were resected during anesthesia. The specimens were processed for visual examination and the detection of inflammatory cells, myelin damage, and intraneural hematoma. The grade of nerve injury was assessed using an objective score ranging from 0 (no injury) to 4 (severe injury).
Results: Fifty-eight nerves, including controls, were examined. According to the applied injury score, there was no significant difference between the pencil-point needle group [median (interquartile range) 3 (3-4)] and the Tuohy needle group [3 (3-4) P = 0.97]. The occurrence of posttraumatic regional inflammation, myelin damage, and intraneural hematoma was similarly high in both groups.
Conclusions: Regardless of the needletip configuration applied for nerve puncture, pencil-point and Tuohy needletips may both lead to comparable magnitude of posttraumatic inflammation and considerable structural changes within the nerve. No significant differences were found comparing pencil-point with Tuohy tip-configured needles.