Lumbosacral transforaminal epidural steroid injection (TFESI) is helpful for the treatment of lumbosacral radicular pain, but in case of intravascular injection, infrequently serious complication can be developed. Against this backdrop, if there is any difference of frequency of intravascular injection incidence during S1 (sacrum 1) TFESI between method using medial approach and method using lateral approach in anteroposterior view, the result can be crucial factor in selecting the approach. In addition, appropriate volume of injection will be checked in each approach.

Inclusion Criteria:

1. Adult patients (20-80 years of age) who were scheduled to receive S1 transforaminal epidural steroid injection for lumbosacral radicular pain at pain management clinic

Exclusion Criteria:

1. pregnancy
2. coagulopathy
3. systemic infection
4. any active infection at the injection site
5. history of allergy to contrast media, local anesthetics, corticosteroid
6. patients unable to communicate or patients with cognitive dysfunction