Have you every watched gymnasts bend backwards? Then run, leap, summersault in the air, and twist and stick the landings with two feet!? It’s incredible. Their arms and legs providing power. Their backs allowing for those highly controlled adjustments in the air. Those slight bends in the spine, at each vertebra*—at least amongst the 24 bones with movable joints—allow for the astonishing mechanics of a human body flipping in the air, and then landing without injury. Would you believe that the ability to do this relies on a tiny joint, smaller than a dime, connecting two stacking vertebrae on both the right side and the left side?
The facet joint is marvelous. It’s not a flat joint, like the intervertebral joint that has a top facing directly up and the bottom facing directly down. Rather, the facet joint has a slight angle, and this allows the parts of the vertebra that stick out in the back—kind of like ears—to slide a little. When this is repeated over each joint, the effect is a smooth curve of the entire back—to either the right, left, backward or forward—without having to create a severe angle at any one joint. And that’s extremely important since this protects the spine from severe injury, and the spine is what houses the spinal cord, which communicates everything between the brain and the neck down.
Unfortunately, like all joints, injuries can cause tiny tears, either along the ligaments connecting the bones or the tissue in between. If these tears don’t heal properly, leading to more inflammation, the nerves nearby may continue to communicate that there is an injury, leading to a persistent pain sensation. A specific nerve along the facet joint, called the medial branch nerve of the dorsal ramus of the spinal nerve, is a little famous amongst interventional pain specialists because it processes both proprioceptive innervation and nociceptive innervation. This means it detects where our bodies are in space, as well as pain. And so small injuries or degeneration to this area can lead to both disability and pain.
After a good physical and neurological exam, a common way for an interventional pain specialist to know whether this nerve might be a source of chronic pain is by doing an anesthetic block. This is short-term pain reducing medicine that is injected along side the nerve and facet joint, under low dose x-ray guidance. It’s a diagnostic procedure. If the patient has improvement in their pain symptoms afterwards, then physician and patient can discuss more permanent pain relief options, like using strong anti-inflammatory medication or radiofrequency ablation.
*Vertebra means a single back bone, and vertebrae means more than one back bone
Angelie Singh, MD, MPH, MS