Thoracic Facet Joint Injection

The thoracic spine is composed of 12 pairs of facet joints. In contrast to the lumbar spine, the superior and inferior articular processes of the thoracic spine cannot be identified separately because the joints are mostly in the frontal plane and they do not face sideward. The articular facets are covered by articular cartilage, and a synovial membrane bridges the margins of the articular cartilage of the 2 facets in each joint. Thoracic facet joints exhibit features typical of a synovial joint. Differences in the thoracic spine are related to the anatomy of pedicles pointing straight backwards and considerably upwards, compared to those in the lumbar region which point slightly laterally, recognizable as a ‘Scotty dog’ configuration. Further the presence of ribs can make visualization more difficult.

Thoracic facet joints have been shown to produce thoracic pain in normal volunteers. Stimulation of thoracic facet joints by distention produces mid back and upper back pain, identical to that seen in patients. This pain can be relieved by anaesthetizing the thoracic facet joints deemed to be responsible for the pain. Pain originating from thoracic facet joints is predominantly present in the upper and mid back.

The pathophysiology of thoracic facet pain remains poorly understood. The thoracic facet joints can be affected by osteoarthritis, rheumatoid arthritis and spondylitis. Degeneration, inflammation, and injury of facet joints can lead to pain upon joint motion, leading to restriction of motion secondary to pain, which eventually leads to overall physical deconditioning. Irritation of the facet joint innervation in itself may lead to secondary muscle spasm. The degeneration of the disc has been assumed to lead to associated facet joint degeneration and subsequent spinal pain.

Presence of degenerative changes does not necessarily mean that the facet joints are the cause of pain. Hence imaging may not necessarily be helpful in management of thoracic facet syndrome.

Patients with thoracic facet joint syndrome commonly present with pain in upper and mid back. Pain can radiate to the scapular area and some times to the anterior chest wall. Pain is exacerbated by standing, bending and twisting movements.

Injections are generally avoided in patients with systemic infection or skin infection over puncture site, bleeding disorders or coagulopathy, allergy to local anaesthetics or any of the medications to be administered.

The procedure is usually done on an outpatient basis. The procedure is performed under fluoroscopic guidance to ensure accuracy of needle placement. Patients need to be aware that the outcome of the procedure is variable and they may not receive the desired benefits. Similarly, they must be aware of the transient nature of the therapeutic benefits and that they may need repeated injections.

Generally a mixture of local anaesthetic and steroid is injected. The local anaesthetic agent within the injectate may act on the nociceptive fibres in the synovium, whereas intracapsular corticosteroids may reduce inflammation of the synovium. The anaesthetic is probably responsible for immediate pain relief, whereas steroids are believed to be responsible for pain relief 2–6 days after their administration. For a diagnostic block, a short-acting anaesthetic alone is sufficient. The role of steroids is controversial, with some studies showing no advantage from the addition of steroids to the injectate.

Complications are rare, particularly if the facet joint injections are performed using a precise needle-positioning technique. Possible complications include spondylodiscitis, septic arthritis, and reaction to the injectates. Septic arthritis can be avoided with appropriate aseptic precautions. Severe allergic reactions to local anaesthetics are uncommon. Steroid injections may produce local reactions, occurring most often immediately after injection. These local reactions last for 24 to 48 hours, and are relieved by application of ice packs. Post-procedural pain flare-up may occasionally occur, and may be treated with pain killers. Neurological complications including paraesthesias, numbness and paralysis have been described but are extremely rare. Infections including epidural abscess and chemical meningitis can occur but the incidence is very low as the procedure is performed under strict aseptic conditions.

In addition, pneumothorax is a well recognized complication of thoracic procedures.

When performed under fluoroscopic visualisation, thoracic facet joint injections are accurate and clinically useful in the diagnosis and therapeutic management of chronic spinal pain. The diagnostic accuracy of facet joint blocks is strong for cervical and lumbar facet joints, and moderate for thoracic facet joints. In contrast to clinical evaluation and imaging techniques, diagnostic injections can identify facet joint pain with a higher level of certainty. However, the diagnostic value is limited by the high false-positive rates seen with single blocks (without control).