How Facet Block Injections Work

A facet joint injection is used to treat chronic neck and back pain. The facet joints, also called the zygapophysial joints, are along the posterior spine. These small bony projections from each vertebra connect the bones of the spine. When the joints become inflamed, pain occurs in the neck and spine.

Why do the facet joints hurt?

To understand facet joint pain, you must first understand how facet joints work. These small joints are affected by arthritis, wear-and-tear, or injury. Damage to the joint’s cartilage affects spinal mobility and can produce debilitating back and/or neck pain. Chronic facet joint pain is diagnosed when pain persists for more than three months. This pain is caused by spinal arthritis, facet degeneration, joint injury, and/or synovial cysts. – 0

What medications are used in facet joint injections?

The injection contains a mixture of a corticosteroid and a local anesthetic. Agents commonly used include:

  1. Betamethasone acetate/betamethasone sodium phosphate – This is a glucocorticoid in the 16 beta-methyl group. This drug works by enhancing the anti-inflammatory action of the molecule and reducing the sodium and water-retaining properties of the fluorine atom bound at carbon 9. Corticosteroids are formed in the adrenal cortex, and have important anti-inflammatory effects. The efficacy of corticosteroids had been demonstrated in many studies, and they affect the action of cytokines, which are chemicals involved in inflammation. In addition, these drugs reduce the accumulation of cellular components in the joint, which reduces pain. Steroidal drug preparations contain corticosteroid esters, which are highly insoluble in water. Betamethasone products provide a dual action of quick onset and long-acting therapy. The duration of action is reported between 14 and 90 days for most corticosteroids.
  1. Bupivacaine hydrochloride – This local anesthetic blocks the generation and conduction of nerve impulses in the body. In addition, it increases the threshold for electrical excitation in the nerve by slowing propagation of the nerve impulse and reducing the rate of action potential. Anesthetics are used to provide local relief of discomfort. They act through inhibition of sodium-specific ion channels on nerve cell membranes, preventing the development of an action potential and inhibiting pain signal transmission.
  2. How are the injections done?

    The neurologist, pain management specialist, or orthopedic specialist will do injections in the office. You must allow an hour for the entire procedure, but the actual injection process only takes around 20-30 minutes. The procedure involves injection a small amount of local injection through the needle to numb the skin. After numbing, the anesthetic and steroid mixture is injected into the facet joints using x-ray guidance. If the first series of joint injections work, but the pain returns, you may have another injection series.

    What happens after the injection?

    The anesthetic will offer immediate pain relief when injected in the facet joint. However, it takes a few days for the steroid to work. The patient should rest for the remainder of the day, and perform activities as tolerated. There will be some soreness at the injection site for 24-48 hours.

    Are facet joint injections effective?

    In a two-year follow-up controlled study, researchers assessed facet joint nerve blocks for effectiveness. The found that the rate of effectiveness was 92% for patients after one year, and around 85% effective after two years. Many clinical studies show significant improvement from facet joint injections. Pain improvement was seen in a recent randomized controlled trial for up to six months.


    Barnsley L, Lord SM, Wallis BJ, Bogduk N. Lack of effect of intraarticular corticosteroids for chronic pain in the cervical zygapophyseal joints. N Engl J Med. 1994;330:1047–50.

    Carette S, Marcoux S, Truchon R, Grondin C, Gagnon J, Allard Y, et al. A controlled trial of corticosteroid injections into facet joints for chronic low back pain. N Engl J Med. 1991;325:1002–7.