Facet joints are small joints at each segment of the spine that provide stability and help guide motion. Facet joints can become painful due to arthritis, back injury, or mechanical stress. With a facet joint block, the doctor can determine if the pain you are suffering is originating from the facet join between the vertebrae. Once his has been determined a injection can provide relief. The mixture of numbing anesthetic and anti-inflammatory steroid medication can have an effect in as little as one or two injections.