Comparison Of Nerve Injury In Scalp Block Performed On Male Wistar Rats (Rattus Norvegicus) Using Sharp Versus Blunt Needles

Abstract

Background: Scalp block is a regional anesthesia technique commonly used in neurosurgical procedures such as craniotomy to reduce perioperative pain, decrease opioid requirements, and maintain hemodynamic stability. However, complications such as nerve injury may occur, and the needle type used plays a critical role. Sharp needles can directly penetrate the fasciculus, leading to axonal injury, while blunt needles tend to cause milder compressive trauma.

Objective: To compare the degree of nerve injury caused by sharp and blunt needles in scalp block using Wistar rats (Rattus norvegicus) as an experimental model.

Methods: A randomized post-test only experimental study was performed on 22 healthy male Wistar rats (6–8 weeks, 150–200 g), divided into sharp and blunt needle groups. Bilateral scalp block was performed at the supraorbital, auriculotemporal, and occipital nerves using 0.2% ropivacaine. After 24 hours, nerve tissue was harvested and examined histopathologically with Hematoxylin–Eosin staining. Injury severity was graded using Steinfeldt’s scoring system (0–4).

Results: The sharp needle group showed significantly higher nerve injury scores than the blunt group. Sharp needles more frequently caused grade 3–4 injuries, particularly at the supraorbital and auriculotemporal sites (p=0.031 and p=0.001), while blunt needles mostly resulted in grade 2 injuries. No significant difference was observed in the occipital block (p=0.108). Overall, injury severity was significantly greater in the sharp needle group (p=0.005).

Conclusion: The type of needle plays a role in determining the degree of nerve injury in scalp block procedures. Blunt needles have been shown to cause less severe nerve damage compared to sharp needles.