Lumbar facet joint injections can provide some pain relief in patients with chronic low back pain emanating from the facet joints. However it is important to note that in some cases injection treatment may not provide the desired results or the pain relief may not be sustained. Overall the current recommendations favour diagnostic lumbar facet joint nerve blocks (medial branch blocks), followed by radiofrequency denervation, rather than intra articular facet injections.
Goldthwait in 1911 first described lumbar facet joints as a source of back pain. In 1933, Ghormley coined the term facet syndrome and defined it as a lumbosacral pain (with or without sciatic pain) that occurs after a twisting or rotary strain to the lumbosacral spine. In 1963 that Hirsch et al injected hypertonic saline into facet joints and experimentally reproduced low back pain along the sacroiliac and gluteal areas with radiation to the greater trochanter. In 1976, Mooney and Robertson, followed by McCall et al. in 1979, used fluoroscopic guidance for facet joint injection with steroids and local anaesthetics.
The facet joints are paired diarthrodial articulations located between the posterior elements of the adjacent vertebrae; also known as zygo-apophyseal joints. They are formed by the articulation of the inferior articular processes of one vertebra with the superior articular processes of the vertebra below. They are typical synovial joints with the facets covered by articular cartilage, bridging synovial membrane, tough fibrous capsule and intervening layer of loose areolar tissue. On the ventral aspect, the capsule is deficient and the joint is in contact with the ligamentum flavum.
The facet joints are richly innervated by the nerve fibres from the medial branch of the dorsal ramus of spinal nerves. Each facet has a dual nerve supply, from the dorsal ramus at the same level as well as from the level above. Each spinal nerve root innervates two facets; it supplies the facet joint at the level it exits, as well as the subsequent lower facet. The exceptions to this dual nerve supply are: singular nerve supply to the atlanto-occipital joint, atlanto-axial joint and C2/3 facet joint, which are innervated by C1, C2 and C3 nerves respectively. Histological studies have shown that capsules of the facet joints are richly innervated with free nerve endings. This means that they are endowed with the appropriate sensory apparatus to transmit proprioceptive and nociceptive information.
Pain of facet joint origin is attributed to a variety of causes, including segmental instability, synovitis, synovial entrapment, trauma, meniscoid impingement and osteoarthritis. Distension and inflammation of the synovial capsule can result in stimulation of the nociceptive nerve endings and the expanded synovial recesses can compress the nerve roots in the spinal canal and neural foramina, thereby causing radiculopathy in patients with facet syndrome. Irrespective of the mechanism, degeneration, inflammation and injury of facet joints can lead to pain upon joint motion. This pain leads to restriction of motion, and eventual physical deconditioning. Irritation of the facet joint innervations can also result in muscle spasm. Pain innervations are also present in other local soft tissue structures adjacent to the joint including the multifidus muscles, the local spinal nerves, and the dura and epidural space. Thus a self-perpetuating painful mechanism is set into motion. Numerous other causes like rheumatoid arthritis, ankylosing spondylitis and capsular tears, have also been described as causes of facet joint pain.
Radiographic changes of osteoarthritis are equally common in patients with and without low back pain, and degenerative joints seen on x rays are not always painful, although some researchers claim that severely degenerated joints are more likely to be symptomatic.
Clinical signs include local paraspinal tenderness; pain that is brought about or increased on hyperextension, rotation, and lateral bending; absence of neurologic deficit; absence of root tension signs; and hip, buttock, or back pain when the straight leg is raised. Symptoms of facet syndrome also include cramping leg pain involving the thigh but generally not radiating below the knee, low back stiffness, and absence of paraesthesia. Low back pain is brought about or increased by maintenance of certain positions, such as sitting erect for a long period of time. Focal tenderness over a facet joint is a strong indication in the appropriate settings, besides the presence of signs of paravertebral spasm or deformity in patients.
It is usually a diagnosis of exclusion, after excluding mimics like nerve entrapment syndrome, discogenic pain, spinal stenosis and osseous abnormalities. In patients with facet joint syndrome, distension of the joint with saline or contrast will reproduce the pain, and injection of a local anaesthetic agent will relieve the pain. This response pattern is the current gold standard for diagnosing the facet syndrome.
The diagnostic injection permits testing of the hypothesis that the target structure (facet joint) is the source of a patient’s pain. Clinical signs are generally unsuitable for making a diagnosis, but may be of value in selecting patients for the diagnostic block of the facet joint.
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 there 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.
When performed under fluoroscopic visualisation, 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). False-positive rates with single blocks are 17%- 47% in the lumbar spine. There is limited literature on the therapeutic efficacy as most of the available data is based on non-controlled and observational studies. There are only few exhaustive randomised control trials available on this subject and they mostly pertain to the lumbar spine. For intra-articular injection of local anaesthetics and steroids, there is moderate evidence of short-term relief and limited evidence of long-term relief of chronic neck and low back pain.
Overall the current recommendations favour diagnostic lumbar facet joint nerve blocks (medial branch blocks), followed by radiofrequency denervation, rather than intra articular facet injections.