Loss of resistance (LOR) is the most commonly used method to confirm the epidural space. The advantage of LOR is its simplicity; only saline or air filled syringe is required. LOR is felt through the sudden decrease of pressure and this pressure gradient is generated when the needle is within the passage of interspinous ligament, ligamentum flavum and epidural space. The presence of ligamentum flavum is crucial for the identification of epidural space by LOR. However, gaps in ligamentum flavum, paravertebral muscle and cyst in interspinous ligament can modify this passage and a false LOR is generated consequentially. The false positive rate of the lumbar and cervical area was reported to be 8.3~17% and 30~68%, respectively. If the false positive rate is high, repeated attempts of epidural steroid injection (ESI) are required, with additional discomfort or pain to the patient.