Technical challenges of performing S1 root block: role for double needle and multilevel needle technique

S1 root block is performed for pain in the lower limbs due to S1 nerve root inflammation at the L5/S1 disc level or compression in the lateral recess. We often note anterior or posterior spread of contrast away from the L5/S1 disc through an anatomically appropriate needle tip placement. We frequently encounter vascular spread when performing S1 root blocks, and the reported incidence varies between 10.4% and 27.8%. There is no clear strategy published to manage these challenges. In such clinical scenarios, we propose a double needle and/or a multilevel needle technique.

A 39-year-old male presented with radicular pain in the left S1 distribution which matched the magnetic resonance imaging (MRI) scan findings and thus he was listed for a left S1 root block. A 22G needle was placed at the S1 level and upon injecting the contrast, vascular spread and anterior and distal spread along the nerve root were noted and the contrast did not reach the site of the pathology, the L5/S1 disc. The contrast continued to spread anteriorly despite withdrawing the needle. A second needle was placed medial and inferior to the first needle and the contrast spread now was adequate, that is, towards the L5/S1 disc and thus the injection was accomplished in a safe and satisfactory manner without needing to reschedule the procedure.

Double needle technique can assist in overcoming problems encountered when performing an S1 root block. The alternatives could be the multilevel technique or to reschedule the procedure or consider a less optimal technique such as a caudal or a lumbar interlaminar epidural. In this technical report, we have highlighted various intervention options to mitigate such challenges and included a flow diagram to assist in decision-making. We have also discussed the possibility of altering the consent to accommodate the changes to the planned procedure.