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Anesthesia

Facet Neck Injections

03/03/2009

Question:

What exactly happens during the injection and how long does it take for the anesthetic to take effect? I`ve read up but nowhere does it state where the injection is given or why you need to come back twice for the other side. Thank you

Answer:

Most pain doctors inject the medial branches (little nerves that supply the facet joints, each joint is supplied by a small nerve from the same level and from the level above), not the joint. There is evidence that injecting the facet joints is not helpful. The injection of the medial branches is typically done for diagnostic purposes, i.e. to figure out whether blocking the nerves are conducting the pain from the facet joints would relieve the pain. Initial diagnostic studies looked at triple paradigms whereby the nerves were injected with a small volume (<0.5 cc or < 10th of a teaspoon) with numbing medicine on two separate occasions and salt water (which should not relieve the pain) as placebo on a different occasions. Only patients who responded to local anesthetics but not the placebo were deemed to truly have facet mediated pain. Later, studies looking at blocking the nerves on different occasions with local anesthetics were also sensitive at predicting facet mediated pain; hence the clinical use of two different diagnostic blocks (to decrease the chance of placebo response). If there is 80-100% pain relief after each of the two diagnostic blocks with local anesthetics, then radiofrequency lesioning should be helpful for a longer term (3-9 months) and sometimes longer especially if physical therapy is maintained. Below are some of the original references for the diagnostic blocks.

Barnsley L et al., Clin J Pain. 1993 Jun;9(2):124-30

Lord SM et al., Clin J Pain. 1995 Sep;11(3):208-13

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Response by:

Salim M Hayek, MD, PhD Salim M Hayek, MD, PhD
Associate Professor of Anesthesiology & Perioperative Medicine
School of Medicine
Case Western Reserve University