Spread of contrast during L4 and L5 nerve root infiltration under fluoroscopic guidance.

Background: Lumbar selective nerve root blocks have been performed to establish the origin of lumbar radiculopathy in clinically difficult cases. The diagnostic ability of selective nerve root blocks remains controversial because of concern over potential spread of an injectate onto adjacent structures.

Objective: To investigate the spread of different volumes of water-soluble contrast during L4 and L5 selective nerve root blocks.

Design: Retrospective, observational case series.

Methods: Analysis of medical records and X-ray images obtained during L4 and L5 selective nerve root blocks.

Results: During L4 selective nerve root block 1 ml of contrast spread onto L5 nerve roots in 46.1% of subjects and during L5 nerve root block 1 ml of contrast spread onto S1 nerve root in 57.7%. There was statistically significant difference (p<0.0001) between spread of contrast onto the medially located nerve root in the same lumbar segment and nerve roots in the lumbar segment above.

Conclusions: Injection of 1 ml of contrast under fluoroscopic guidance does not guarantee selective spread of the contrast around L4 or L5 nerve roots only. There is also spread toward the more medial nerve root in the same spinal segment during L4 and L5 nerve root infiltration. These findings suggest that it is possible to differentiate between L4 and L5 nerve root pathology using a sequential nerve root blocks under fluoroscopic guidance.