Injections of local anesthetic into the facet (zygapophyseal) joints can be diagnostic.
If steroids are added, the effect is therapeutic, but not diagnostic. These injections are generally easy to perform unless the joints are extremely arthritic. The facet joints in the lumbar spine are roughly “S” shaped on x-ray. The volume they will accommodate is very small with some lumbar joints accepting only ½ cc of solution before the joint ruptures. Once joint rupture occurs, the local anesthetic injected anesthetizes several other structures, and the diagnostic utility is lost. Therefore only very small quantities are to be injected if the block is to be deemed diagnostic.
Usually, this precludes the use of any steroid in the joint because the ½ cc volume is exceeded when combining a local anesthetic and a steroid. All facet injections must be performed under fluoroscopy (x-ray).
Some patients are given IV sedation for the procedure. Usually the procedure is relatively rapid, requiring about 5 minutes per joint blocked. On occasion, as a part of a pain mapping sequence, a block will be performed followed by awakening and walking to reassess the pain.
Other blocks may follow on the same day in order to pinpoint the pain sources.
The cervical facets are often responsible for whiplash injury pain in over 50% of the time.
These joints are also blocked using fluoroscopy. Therapies used once a positive diagnostic block is obtained include laser, RF, and cryoneurolysis of the facet joints.