Are diagnostic lumbar medial branch blocks valid? Results of 2-year follow-up

The precise cause of low back pain based on clinical history, physical examination, radiological imaging, and electrophysiological testing can be identified in only 15% of patients in the absence of disc herniation and neurological deficit. The prevalence of chronic lumbar zygapophysial (facet) joint pain ranges from 15% to 45% utilizing comparative local anesthetic blocks in controlled settings in accordance with the criteria established by the International Association for the Study of Pain. Currently, facet joint injection procedures are considered as the gold standard in the diagnosis of facet joint pain. Facet blocks have been criticized as lacking diagnostic validity, along with other tests, including discography, neurophysiologic tests, stress radiographs, x-ray studies, bone scintigraphy, thermography and diagnostic ultrasound. However, these assumptions have been based on biased evaluations without consideration of the criteria of the International Association for the Study of Pain, as well as the nature of controlled diagnostic blocks. Utilizing the criteria established by the Agency for Healthcare Research and Quality (AHRQ) for Systems to Rate the Strength of Scientific Evidence, it was shown that the validity, specificity, and sensitivity of facet joint nerve blocks are considered strong in the diagnosis of facet joint pain. The accuracy of a diagnostic test is best determined by comparing it to an appropriate reference standard, such as biopsy, surgery, autopsy or long-term follow-up. Since we are unable to apply reference standards of biopsy, surgery, or autopsy, and pain relief has been argued as an inconsistent feature, long-term follow-up has been considered as the best indicator. This study was undertaken to evaluate stability of the diagnosis of lumbar facet joint pain following comparative local anesthetic blocks at a follow-up after 2 years. The results showed that 85% of the patients available for follow-up withstood the diagnosis of facet joint pain at the end of 2 years, whereas this proportion decreased to 75%, if all the patients in the study were included in the analysis.