Lumbar Medial Branch Blocks

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AP fluoroscopy image of left L3 and L4 medial branch and L5 dorsal ramus blocks.
Lumbar Medial Branch Blocks
Indication	Diagnostic test for Lumbar Zygapophysial Joint Pain
Syringe	3mL syringe
Needle	22-25g 3.5 inch spinal needle with a bent tip
Steroid	Not appropriate
Local	1-4% lidocaine or 0.5-0.75% bupivacaine
Volume	0.5mL over each targeted nerve

Controlled lumbar medial branch and L5 dorsal ramus blocks are the only validated tool for diagnosing lumbar zygapophysial joint pain.

Anatomy

Each zygapophysial joint is innervated by two nerves and so both need to be anaesthetised. At the L1-4 neural segments the target is the medial branch of the dorsal ramus. At the L5 neural segment the target is the L5 dorsal ramus. The medial branches at each level are located at the junction of the superior articular process (SAP) and transverse process (TP) of the level below. The L5 dorsal ramus is at the junction of the S1 SAP and sacral ala. The L4 medial branch is found at the junction (jx) of the L5 SAP and TP, etc.

Joint	Inferior innervation	Superior innervation
L5/S1 facet joint	L5 dorsal ramus at S1 jx SAP and sacral ala	L4 medial branch at L5 jx SAP and TAP
L4/5 facet joint	L4 medial branch at L5 jx SAP and TP	L3 medial branch at L4 jx SAP and TAP
L3/4 facet joint	L3 medial branch at L4 jx SAP and TAP	L2 medial branch at L3 jx SAP and TAP

The medial branches run at what is called the "inflexion" which is the curve between the base of the SAP and the upper border of the TP and the mamillo-accessory ligament. There is no mamillo-accessory ligament at S1. The mamillo-accessory ligament passes between the mamillary process on the base of the superior articular process and the accessory process on the proximal end of the transverse process.

Indications

The indication is chronic low back pain that is not responding to conservative management to assess whether the pain is arising from one or more lumbar zygapophysial joints. Positive blocks can lead to the validated treatment option of radiofrequency neurotomy. It is the primary test in the older patient where zygapophysial joints may account for 40% of axial pain. In younger patients zygapophysial joint pain is usually only considered when discogenic pain has been excluded.

Pre-Procedural Evaluation

Obtain adequate consent. An emphasis should be placed on this procedure being a test not a treatment. This concept should be repeated several times and also be provided in written information. The concept can be reinforced through visual means by drawing a pain graph for the patient showing the expected response with pain going back up to baseline. Despite all this some patients may still be surprised that the pain came back after the anaesthetic wears off.

Appropriate target(s) should be selected. The majority of positive cases are found to be single level and unilateral. Injections of >2 levels and routine bilateral injections are not supported.

Premedication is not recommended because it can interfere with the interpretation of the results. If the patient cannot tolerate the procedure without premedication due to anxiety then the anxiety should be treated first rather than proceeding to medial branch blocks.

No physiological monitoring or intravenous access is required.

Before the procedure the patient records a pain diagram, their pain ratings (worst ever experienced, worst ever for index pain, and index pain on day of procedure), and four activities that are limited by the index pain. The recording sheet has a section for recording the pain before, immediately following, and several hours after the procedure, along with an area for recording whether painful activities are restored.

Technique

L1-L4 Medial Branches

• Preparation
  • Position: Patient is prone with a pillow under their abdomen in order to decrease the lordosis.
  • Prep and drape
• Target visualisation
  • Under fluoroscopy first evaluate the lumbosacral region for transitional anatomy
  • Palpate the spine to find the level to be tested. Use maximal point tenderness.
  • Position the C-arm so that the target vertebra is in the middle
  • "Square off" the superior endplate. This refers to tilting the C-arm cephalo-caudally so that the beam is parallel to the endplate. For example if the target is the L4 medial branch at L5 then square off the superior endplate of L5
  • Rotate the C-arm ipsilaterally to obtain an oblique view. Visualise the inflexion point between the SAP and TP, usually this is at about 40 degrees.
  • The target is approximately 1/3 to 1/2 the distance between the inflexion and mamillary process.
• Needle placement
  • Optional local anaesthetic intradermally
  • Insert spinal needle slightly lateral to target, go down the beam, and advance until bone is contacted
  • Confirm needle position in AP view. The needle tip should be located right at or slightly medial to the lateral margin of the SAP
  • Use a decline view to confirm needle tip location. The tip should point into the notch located between the SAP and TP.
  • If there is concern about depth an inadvertent entry into the foramen then obtain a lateral view
  • Twist needle so that the bevel faces medially
• Injection
  • Connect a low volume extension tube to the syringe
  • Contrast: inject 0.1-0.3 mL of contrast under live fluoroscopy. Observe for aberrant flow especially venous uptake which can lead to a false negative. The contrast should cover the path of the medial branch. The decline view can again be used to confirm spread.
  • Inject 0.3-0.5mL of local anaesthetic

Post-Procedural Evaluation

The patient should be evaluated 30-60 minutes post-injection. It is ideal if the evaluator is independent and also blinded to the anaesthetic used.

A positive test requires close to 100% relief of the index pain with provocative movement. 80% relief may be considered when residual pain is <1/10.

A 30% false positive rate is seen, and so controlled blocks are required prior to undertaking radiofrequency neurotomy.