Incidence of genitofemoral nerve block during lumbar sympathetic block: comparison of two lumbar injection sites.

Background and objectives: Genitofemoral nerve (GFN) block is a known side effect of a lumbar sympathetic block (LSB), although the incidence has not been well documented. Furthermore, genitofemoral neuralgia can occur following neurolytic LSB. Because the level at which the GFN exits the psoas sheath varies, this study was designed to identify differences in the incidence of GFN block following LSB at the level of the second versus the fourth lumbar vertebrae.

Methods: Patients requiring LSB to evaluate chronic lower extremity pain were prospectively studied. Patients were injected at the second lumbar (L2 group) or fourth lumbar (L4 group) vertebral body depending on the location of the pain syndrome in the lower extremity. Lumbar sympathetic blocks were performed using 10 mL of a 0.5% bupivacaine solution with radiocontrast; spread of injectate was verified using fluoroscopy. An observer evaluating for presence of GFN block was blinded to the lumbar level of injection.

Results: Thirty patients were enrolled (L2 group, n = 15; L4 group, n = 15). Spread of local anesthetic/radiocontrast solution was limited to approximately one vertebral body above and one below the target level. There was no difference in the ability to achieve a LSB; success rates were 66% and 73% using L2 and L4, respectively. The incidence of GFN block was 0% (0/15) in the L2 group versus 40% (6/15) in the L4 group; this was statistically significant (P = .017, Fisher's exact test).

Conclusions: The GFN is less likely to be blocked when the LSB is performed near the second lumbar vertebra as compared with the fourth lumbar vertebra.