Facet joint pain typically presents with low back pain with, or without referred pain into the leg. Studies have shown that facet joints can be damaged in accidents (e.g. motor vehicle accidents), and that these changes in the facet joints may not show up on x-ray, CT scan or MRI scanning.
The only way to determine whether the facet joints are the cause of pain is to inject the joint or its nerve supply with local anaesthetic. If pain is substantially eliminated while the anaesthetic is acting, it is assumed that the facet joint is the source of pain. This injection process is known as a block (the aim is to block out the pain). The nerve supply to the facet joint is via the medial branches of the adjacent dorsal rami (branches of nerves), which originate from the spinal nerve. Thus, blocks of the nerve supply to the facet joints are called medial branch blocks.
Studies show that a successful block means that there is a 70 per cent chance that the diagnosis is facet joint pain. That means, false positive blocks (blocks that incorrectly diagnose the facet joints to be causing the patient’s symptoms) do occur. A second positive block using other anaesthetic agents increases the diagnostic confidence to 90 per cent.
Medial branch blocks are used for stubborn chronic pain if specific treatment to the facet joint is required. This treatment is known as radiofrequency neurotomy (RFN), or radiofrequency denervation. This treatment applies heat lesions to the nerve and can lead to prolonged pain relief.