Nerve perforation with pencil point or short bevelled needles: histological outcome

Background In the case of needle nerve contact during peripheral blocks, pencil point needles are considered less traumatic compared with bevelled needles. However, there are not enough data to prove this notion. Therefore, the aim of this study was to challenge the hypothesis that nerve perforation with short bevelled needles is associated with major nerve damage compared with pencil point needles. Methods In five anaesthetised pigs, the brachial plexus was exposed bilaterally. Up to eight nerves underwent needle nerve perforation using a pencil point needles cannula or an short bevelled needle. After 48 h, the nerves were resected. The specimens were processed for visual examination and the detection of inflammatory cells (haematoxylin-eosin, i.e. CD68-immunohistochemistry to detect macrophages), myelin damage (Kluver-Barrera staining) and intraneural haematoma. The grade of nerve injury was characterised by an objective score ranging from 0 (no injury) to 4 (severe injury). Results Fifty nerves were examined. According to the injury score applied, there was no significant difference between the pencil point needles [median (inter-quartile range) 2.0 (2.0-2.0)] and the short bevelled-needle group [median 2.0 (2.0-2.0) P=0.23]. No myelin damage was observed. Signs of post-traumatic inflammation were equally distributed among both groups. Conclusions In the present study, the magnitude of nerve injury after needle nerve perforation was not related to one of the applied needle types. Post-traumatic inflammation rather than structural damage of nerve tissue is the only notable sign of nerve injury after needle nerve perforation with either needle type. However, neither the pencil point- nor the short bevelled needle can be designated a less traumatic device.