Long-term experience with implanted intrathecal drug administration systems for failed back syndrome and chronic mechanical low back pain

BACKGROUND Continuous intrathecal drug delivery has been shown in open studies to improve pain and quality of life in those with intractable back pain who have had spinal surgery. There is limited data on long term effects and and even less for patients with mechanical back pain without prior spinal surgery. METHODS We have investigated spinal drug administration systems for patients with failed back syndrome and chronic mechanical low back pain by patient questionnaire study of the efficacy of this therapy and a case notes review. RESULTS 36 patients (97% of 37 approached) completed questionnaires, 24 with failed back syndrome and 12 with chronic mechanical low back pain. Recalled pre-treatment levels with current post-treatment levels of pain and a range of quality of life measures (recorded on 11-point numerical rating scales) were compared. Pain improved significantly in both groups (Wilcoxan signed ranks test, p < 0.005). The majority of quality of life measures improved significantly in the failed back syndrome group (Wilcoxan signed ranks test, p < 0.005) although work interruption and the effect of pain on sex life did not change. There was a trend towards improvement in the majority of quality of life measures in the mechanical back pain group but this did not reach statistical significance due to the smaller numbers in this cohort (p > 0.005, Wilcoxan signed ranks test with Bonferroni correction).Diamorphine was used in all 37 patients, bupivacaine in 32, clonidine in 27 and baclofen in 3. The mean dose of diamorphine increased for the first 2 years but did not change 2-6 years post implant, averaging 4.5 mg/day. Revision surgery was required in 24% of cases, but reduced to 12% in the later years of our experience. CONCLUSIONS We conclude that spinal drug administration systems appear to be of benefit in alleviating pain in the failed back syndrome and chronic mechanical low back pain but need to be examined prospectively.