The role of needle tip position on the accuracy of diagnostic selective nerve root blocks in spinal deformity

Abstract

The specificity of a selective nerve root block (SNRB) is dependant on isolating only the required nerve root whilst avoiding injectate flow to traversing nerves. Needle tip position is therefore crucial. Nerve root blocks (SNRBs) in the presence of deformity can be particularly technically challenging to perform. The aims of this study were to document the relationship of needle tip position and SNRB accuracy in patients with and without spinal deformity. Over an 8-month period, all SNRBs performed by one spinal surgeon were included. Patients with radiographic evidence of spinal deformity were analysed separately and their lumbar deformity graded using the Schwab grading system. Needle tip position in relation to the superior pedicle and flow of contrast was documented. 76 patients received 85 injections without deformity, 26 patients with deformity underwent 30 SNRBs. In the normal spinal alignment group, there was on overall accuracy of 70.1% regardless of needle tip position, which improved to 91.8% for a lateral needle tip position (P < 0.001). In patients with deformity, the overall accuracy was significantly lower irrespective of needle tip position 36 versus 70%, respectively (P < 0.0019). Selective nerve root blocks are accurate in patients without deformity where a needle tip placement lateral to the middle third of the pedicle is achieved. The presence of spinal deformity significantly reduces the accuracy of SNRBs with a higher chance of epidural infiltration.