Background: Lumbar facet (zygapophysial) joints have been implicated as the source of chronic pain in 15% to 45% of patients with chronic low back pain. Diagnosis may be confounded by false-positive results with a single diagnostic block and administration of anxiolytics and narcotics prior to or during the diagnostic facet joint blocks.
Objective: To evaluate the effect of midazolam and fentanyl on the diagnostic validity of of lumbar facet joint pain.
Study Design: Randomized, prospective, double-blind, placebo-controlled evaluation.
Methods : The design consisted of a placebo group receiving sodium chloride solution and two experimental groups receiving either midazolam or fentanyl. The patients included in the study were diagnosed with facet joint pain with controlled comparative local anesthetic blocks of medial branches or L5 dorsal rami. They had been treated with lumbar facet joint nerve blocks with good pain relief, and were presenting for repeat treatment after a period of symptom relief.
The study was undertaken in an interventional pain management practice.
Outcome Measures: Outcomes were assessed at baseline and after the administration of 1 of the 3 solutions (Group I, sodium chloride solution; Group II, midazolam; or Group III, fentanyl).
Outcome measures included numeric pain scale, proportion of pain relief, and ability to perform prior painful movements.
Results: Pain relief of >80% was noted in 2% of the patients in Group I, 5% of the patients in Group II, and 7% in Group III. Pain relief of >50% was noted in 7% of the patients in Group I, 5% of the patients in Group II, and 13% of the patients in Group III. There were no significant differences among the groups.
Conclusion: The administration of sedation with midazolam or fentanyl is a confounding factor in the diagnosis of lumbar facet joint pain in patients with chronic low back pain. However, this study suggests that if strict criteria including pain relief and ability to perform prior painful movements is used as the standard for evaluating the effect of controlled local anesthetic blocks, the diagnostic validity of lumbar facet joint nerve blocks may be preserved.
Keywords: Chronic low back pain, lumbar facet joint pain, controlled comparative local anesthetic blocks, false-positives, confounding factors, analgesia