Epidural steroids are commonly administered in the treatment of "failed back surgery syndrome." Because patient response is dependent on accurate steroid placement, fluoroscopic guidance has been advocated. However, because of ever-increasing medical expenditures, the cost-benefit of routine fluoroscopy should be critically evaluated. Therefore, 50 patients were enrolled into this institutional review board-approved, prospective, controlled, single-blinded study. At a predetermined intervertebral level, the epidural space was identified using an air loss of resistance technique. Thereafter, an epidural catheter was inserted 2 cm through the epidural needle. To determine the accuracy of the clinical placement, contrast medium was administered through the epidural catheter; antero-posterior and lateral lumbar spine radiographs were then obtained. The number of attempts required to successfully locate the epidural space, the reliability of the air loss of resistance technique in indicating successful epidural penetration in failed back surgery syndrome, the ability of the clinician to accurately predict the intervertebral space at which the epidural injection was performed, and the spread of contrast medium within the epidural space were recorded. A total of 48 epidurograms were performed. The number of attempts to successfully enter the epidural space was 2 +/- 1. In 44 cases, the radiological studies confirmed the clinical impression that the epidural space had been successfully identified. In three patients, the epidural catheter was in the paravertebral tissue. One myelogram was recorded. In 25 patients, the epidural catheter did not pass through the predetermined intervertebral space. In 35 cases, the contrast medium did not reach the level of pathology.
Implications: The clinical sign of loss of resistance is a reliable indicator of epidural space penetration in most cases of "failed back surgery syndrome." However, surface anatomy is unreliable and may result in inaccurate steroid placement. Finally, despite accurate placement, the depot-steroid solution will spread to reach the level of pathology in only 26% of cases.