Anatomy of Lumbar Facets

Spinal anatomy is a remarkable combination of strong bones, flexible ligaments and tendons, large muscles and highly sensitive nerves. It is designed to be incredibly strong, protecting the highly sensitive nerve roots, yet highly flexible, providing for mobility on many different planes. Most of us take this juxtaposition of strength, structure and flexibility for granted in our everyday lives - until something goes wrong. Once we have back pain, we're driven to know what's wrong and what it will take to relieve the pain and prevent a recurrence.





Origin of Pain

The lumbar spine refers to the lower back, where the spine curves inward toward the abdomen. It starts about five or six inches below the shoulder blades, and connects with the thoracic spine at the top and extends downward to the sacral spine. A joint is where two or more bones are joined. Joints allow motion (articulation). The joints in the spine are commonly called Facet Joints. Other names for these joints are Zygapophyseal or Apophyseal Joints. Each vertebra has two sets of facet joints. One pair faces upward (superior articular facet) and one downward (inferior articular facet).

Producing Back Pain

There is one joint on each side (right and left). Facet joints are hinge–like and link vertebrae together. They are located at the back of the spine (posterior).Facet joints are synovial joints. This means each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing joints to move or glide smoothly (articulate) against each other. These joints allow flexion (bend forward), extension (bend backward), and twisting motion. Certain types of movement are restricted. The spine is made more stable due to the interlocking nature to adjacent vertebrae.

Causes of Back Pain

Many different structures in the spine can cause back pain, potentially when:

  • The large nerve roots that go to the legs and arms are irritated
  • The smaller nerves that innervate the spine are irritated
  • The large paired back muscles (erector spinae) are strained
  • The bones, ligaments or joints themselves are injured
  • The disc space itself is a source of pain

Therefore, a review of spinal anatomy is important to understand the causes of back pain, neck pain, and sciatica (leg pain), and evaluate treatment options.

Applications For Lumbar Facet Pain Control

What is a medial branch nerve?

The medial branch is the branch of the spinal nerve that carries sensation and pain signals from the facet joint back to the spinal cord.

What are the indications for a facet joint injection or medial branch block?

These injections are performed as a diagnostic test when it is thought that a facet joint or joints is part of the process that is causing the pain. A small amount of a local anesthetic is injected into the joint or over the medial branch nerve to see if this will temporarily relieve your back pain.

How long will the pain relief last after a facet joint injection or medial branch block?

The local anesthestic block will only last a few hours. A small amount of steroid may be injected along with the local anesthetic and may provide pain relief from days to months.

How do the facet joints cause pain?

The facet joints are just like any other joint in the body, they are succeptable to acute injury (sprain or strain) as well as degenerative arthritis. In the back, the facet joints may cause low back pain, hip and buttock pain, and leg pain. The pain is especially bad when leaning backwards or twisting your spine. The pain also tends to be worst first thing in the morning and in the evening.

What if a facet joint injection does not improve my pain?

Facet joint injections or medial branch blocks are performed to diagnose pain being caused by the facet joints in your back and will not relieve pain caused by intervertebral discs, spinal nerves, or muscles, which can continue to cause pain after the procedure. If your pain is not relieved after the procedure, the facet joints have been ruled out as the source of your pain.

What if the facet joint injection is successful?

If the facet joint injection successfully treat your pain for a significant period of time, they may be repeated as necessary. If the facet joint injection relieves your pain for a short period of time, then you will likely be scheduled for radiofrequency ablation (RFA) of the medial branch nerves.

Are there any restrictions following the facet joint injection?

We ask that you not immerse in water for 24 hours after the injections. This means that you can shower, but not take a bath or go swimming for the rest of the day. There are no other specific restrictions on activity however, we recommend that you "take it easy" the rest of the day and slowly resume your normal activities.

What are the risks of the facet joint injection?

Overall, facet joint injections (and medial branch blocks) are a very safe procedure. Serious side effects or complications are rare, however, like all injection procedures, possible adverse effects are possible. The most common complications include bleeding and bruising at the needle puncture site, post-procedure headaches, and lightheadedness or dizziness immediately following the procedure. Other very rare complications include transient numbness or weakness, paralysis (partial or complete), contrast or allergic reactions, sexual dysfunction, and death. If you experience any concerning symptoms after your injection, you should call your doctor immediately or go to an emergency room for evalulation.

Anatomic Formation

The anatomical, biomechanical and physiological characteristics of the facet joints in the cervical and lumbar spines have become the focus of increased attention recently with the advent of surgical procedures of the spine, such as disc repair and replacement, which may impact facet responses. In order to better understand the physiological implications of tissue loading in all conditions, there are many reviews of mechanotransduction pathways in the cartilage, ligament and bone is also presented ranging from the tissue-level scale to cellular modifications.

Posterior Spinal Segment

Experimental studies are showed as they relate to the most common modifications that alter the biomechanics and health of the spine-injury and degeneration.





Technique

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

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.

Clinical outcome?

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