Electron microscopy evaluation of block needle‐related trauma to the tibial nerve

Background: Direct puncture by a needle is a risk factor for nerve damage. This investigation used scanning electron microscopy (SEM) to attempt to visualize the damage caused by different needles. Method: A 15 cm section of the tibial nerve was removed from the ankle of a patient undergoing below‐the‐knee amputation. The nerve specimen was punctured perpendicular to the fibers once by each of four needles: an insulated 22 G short‐beveled (30°), a 25 G long‐beveled Quincke spinal needle, an 18 G Tuohy, and a 25 G Whitacre pencil point. The distal and proximal ends on either side of the needles were marked and the nerve was sectioned into 0.5 cm pieces. Each sample was preserved and then prepared for SEM. The needle tract was observed for evidence of mechanical damage at magnifications between × 47 and × 102 using SEM. Results: The epineurium, perineurium, fascicles, endoneurium, and vessels were identified in each sample. In both the short‐beveled and the Whitacre samples, all fascicles along with the surrounding perineurium were intact. In both the Tuohy and the Quincke samples, obvious transection of fascicles and disruption of the perineurium were observed. Conclusions: This investigation suggests that both the Tuohy and the Quincke needles may be more likely to cause trauma to the tibial nerve than either the short‐beveled or the Whitacre needles.