DOES THE POSITION OF INJECTION AFFECT OUTCOME OF SACRAL EPIDURAL INJECTION FOR SCIATICA? A PILOT STUDY

Abstract

Purposes: To determine the effect of gravity on outcome in sacral epidurals injected in the prone compared to the lateral position in patients with unilateral back related leg pain.

Methods: A randomised controlled trial with 2 arms. This pilot study was conducted to determine the standard deviation (SD) of the primary outcome measure to allow calculation of a final sample size. Forty patients who met the inclusion/exclusion criteria were randomly allocated to prone or lateral sacral epidural injection. Twenty patients were allocated to the prone and 20 to the left or right lateral position dependent on their radicular back pain. The primary outcome measure of back and leg pain severity was assessed using a visual analogue scale (VAS) (0= none, 10 = worst imaginable). The Oswestry disability index, SF-36 and straight leg raise were also measured. Outcomes were assessed at baseline and at 6 and 12 week follow-up. A repeated measures analysis using mixed model methodology was used to determine statistical significance.

Results: The 2 groups were comparable in gender and age. The prone group had a mean improvement in VAS back pain score at 6 weeks follow-up of 0.5 compared to 1.6 in the lateral group. At 12 weeks follow-up there was a negative response of 0.1 compared to baseline in the prone group and 1.4 improvement in the lateral group. Repeated measures analysis showed no significant difference in back pain scores between the groups at the 5% level (F2,38 = 3.24; P = 0.0797). Similarly mean improvement in VAS leg pain scores at 6 weeks follow-up were 1.4 in the prone group and 1.7 in the lateral group. At 12 weeks follow-up the scores were 1.1 for the prone and 2.4 for the lateral group. Repeated measures analysis showed no significant difference in leg pain scores between the groups (F1,38= 0.76; P = 0.3898). A post-hoc power calculation using the sample VAS SD showed we had reached only 65% power.

Conclusion: This pilot study has shown that sacral epidural injection for sciatica in the lateral position gives superior pain relief compared to the prone position but the difference is not statistically significant. More patients will now be recruited in order to minimise a type II error that may have occurred.