Caudal epidural block is useful not only for regional anesthesia of low abdominal, perineal area or lower extremities but for relieving acute or chronic pain of low back and lower extremities. Recently, there were some reports that there was a difference of the contrast flow pattern during lumbar epidural block according to a location of needle tip in the lumbar epidural space. Therefore, the investigators hypothesize that there is a difference of contrast flow pattern in caudal epidurography when a needle is inserted with intentionally lateral direction.

Inclusion Criteria:

• patients with unilateral radiculopathy

Exclusion Criteria:

• patients with sepsis
• chronic infection
• coagulopathy
• local infection near the sacral hiatus
• the allergy of the contrast
• history of spine surgery, scoliosis and kyphosis

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