Volume of contrast and selectivity for lumbar transforaminal epidural steroid injection.

BACKGROUND It has been shown that L4/L5 selective nerve root blocks become nonselective after injecting 1 mL and 0.5 mL of contrast. Volumes of less than 0.5 mL have not been used to determine a volume of definite specificity. OBJECTIVE This study attempts to identify the minimum volume of contrast at which selectivity is maintained without spread to the superior or inferior end plate. STUDY DESIGN Prospective, nonrandomized, observational human study of 70 patients receiving lumbar transforaminal epidural steroid injection. METHODS Using biplanar imaging, needle tip position was confirmed just caudad to the pedicle shadow at 6 o'clock position in the AP view and mid or ventral aspect of the foramen in the lateral view. Contrast was then injected in aliquots of 0.2 mL to a total volume of 2.0 mL. Fluoroscopic images were recorded at 0.2 mL increments. These images were evaluated to determine which 0.2 mL volume increment was no longer specific. Volume of contrast at which the spread extended to the superior and inferior end plates and crossed the midline to the contralateral side was also recorded. RESULTS Three patients had extraforaminal flow and one had an initial intravascular injection. Data were analyzed for 66 patients. Average (s.d) volume of contrast at which selectivity was demonstrated was 0.41 mL (0.26). Superior and inferior spread was noted at 0.82 mL (0.49) and 0.83 mL (0.44), respectively. Seventy-eight point eight percent of SNRB were selective for the specified nerve root after injecting 0.2ml of dye. Selectivity decreased to 33.3% after injecting 0.6 mL; 1.2 mL of dye injected was selective only in 6% of patients. Superior spread of contrast was more common as compared to inferior (P = 0.016). Also, initial spread was superior in 50% of cases at L4 level and 64.7% at L5 level (P <0.05). LIMITATIONS Relatively small number of patients with a nonrandomized design. CONCLUSIONS Diagnostic selective nerve root blocks limiting injectate to a single, ipsilateral segmental level cannot reliably be considered diagnostically selective with volumes as low as 0.2 mL. Also, spread of the contrast to the superior nerve root was more likely than spread to the inferior nerve root.