Facet Joint Pain & Medial Branch Blocks

Medial Branch Block Technique

Medial branch blocks (MBBs) are the reference standard for diagnosing facet-mediated pain. The technique targets the small medial branch nerves of the dorsal rami that innervate the facet joints.

Understanding Dual Innervation

Each lumbar facet joint receives innervation from two medial branch nerves:

• The medial branch at the same level as the superior articular process
• The medial branch from one level above

Example: The L4-5 facet joint is innervated by:

• The L3 medial branch (courses over the L4 transverse process)
• The L4 medial branch (courses over the L5 transverse process)

Practical implication: To completely block or denervate a single facet joint, two nerves must be targeted.

Special case — L5-S1: Innervated by the L4 medial branch and the L5 dorsal ramus (not a medial branch — the L5 dorsal ramus has a different anatomical course along the ala of the sacrum).

Anatomical Targets

• L1-L4 medial branches: Target is the junction of the transverse process and the superior articular process (SAP) at the level below (e.g., L3 medial branch targeted at junction of L4 TP and L4 SAP)
• L5 dorsal ramus: Target is the junction of the S1 SAP and the sacral ala
• Cervical medial branches: Course over the waist of the articular pillar at each level — more consistent anatomy than lumbar

Cervical MBB Technique Details (IPSIS)

Cervical medial branch anatomy and blocking technique differ from the lumbar spine in important ways:

Third Occipital Nerve (TON) — C2-3 Joint

• The C2-3 joint is uniquely innervated by the TON (superficial medial branch of the C3 dorsal ramus), not by a typical medial branch pair
• The TON varies in position from superior to inferior along the lateral C2-3 joint, so three target points are used along the longitudinal bisector of the joint (at the C3 SAP apex, base, and equator)
• Total local anesthetic volume for a 3-injection TON block: 0.6 mL (0.2 mL per target)
• Contrast use is prudent at the TON level given the possibility of aberrant vertebral artery loops near the target

Typical Cervical Levels (C3-6)

• The medial branches course along the waist (concavity) of their respective articular pillars
• The target is the centroid of the articular pillar — the intersection of two diagonals of the diamond-shaped pillar
• A single block point at the centroid is sufficient to anesthetize the medial branch at each typical level
• Recommended local anesthetic volume: 0.25 mL per level (lower than older protocols that used 0.5 mL, to improve diagnostic specificity)
• True lateral segmental imaging is essential — the bilateral articular pillars must be superimposed for accurate target identification

C7 Medial Branch

• The C7 medial branch is not associated with an articular pillar but crosses the C7 SAP or the base of the C7 transverse process
• Its variable location requires three target points: SAP apex, SAP base near the TP junction, and a third point slightly superficial to the SAP apex
• Total local anesthetic volume: 0.6 mL (0.2 mL at each of three targets)
• Contrast is optional at C7 because multiple injections are performed, and residual contrast from one target may obscure subsequent placements

Patient Positioning for Cervical MBBs

• Lateral approach: patient may be lateral decubitus (target side up), supine, or prone with a laterally positioned fluoroscope
• Posterior approach: patient prone with chest bolster to flex the neck; fluoroscope is declined caudally to reveal the articular pillar waists (pillar view)

Lumbar MBB Technique Details (IPSIS)

Anatomy and Target Acquisition — L1-4 Medial Branches

• The bony target lies one-third to one-half the distance along an imaginary line from the inflection (curve between SAP base and TP) to the mamillary process
• The SAP is often angled from medial to lateral in the axial plane, which requires ipsilateral fluoroscopic obliquity (typically 30-40 degrees) to access the medial branch without the needle being deflected laterally by an overhanging dorsal SAP
• Bulbous (mushroom-shaped) SAPs from osteoarthritic changes may demand additional obliquity
• The mamillo-accessory ligament (MAL) covers the nerve at L1-4 levels — if the needle sits atop the MAL rather than beneath it, anesthetic may not reach the target, causing a false-negative block

L5 Dorsal Ramus Target

• The L5 dorsal ramus is targeted in the groove (sulcus) between the S1 SAP base and the sacral ala
• There is no MAL at S1
• A high-riding iliac crest may obstruct access; increasing the cephalad fluoroscopic tilt to square off the S1 endplate usually displaces the crest enough
• The needle must never stray cephalad to the S1 SAP/sacral ala notch (risking the L5 nerve root) or too far inferiorly toward the posterior S1 foramen

Lumbar Injectate Volumes

• Contrast: 0.1-0.3 mL to confirm spread and rule out venous uptake
• Local anesthetic: 0.25-0.5 mL per nerve (volumes as low as 0.25 mL may be sufficient)
• A declined fluoroscopic view helps confirm that contrast fills the notch between the SAP and TP

Thoracic MBB Considerations (IPSIS)

Thoracic medial branch procedures remain an area of evolving understanding:

• Recent anatomic studies have challenged the traditional assumption that thoracic facet joint articular branches arise from the distal medial branch (as in the lumbar spine)
• Multiple cadaveric dissections have found that articular branches at T1-9 frequently arise directly from the dorsal ramus or very proximal medial branch, near the neural foramen — not from the distal medial branch where blocks and RF lesions are traditionally placed
• At T10, the medial branch crosses the superolateral corner of the transverse process in about 70% of specimens (and just cranial to it in 30%)
• At T11, the course is more constant over the superolateral TP corner
• At T12, the anatomy resembles the lumbar medial branch pattern
• Despite these anatomic uncertainties, if diagnostic TMBBs achieve 80-100% relief, it is reasonable to expect that radiofrequency coagulation at the same site would extend that pain relief

Step-by-Step Technique (General)

1. Patient positioning: Prone on fluoroscopy table
2. Level identification: AP fluoroscopy to identify target transverse processes
3. Needle placement: 22-25 gauge spinal needle advanced to the junction of the TP and SAP under fluoroscopic guidance
4. Confirm position: AP and lateral views to verify needle tip at the target
5. Contrast injection: Small volume (0.1-0.3 mL) to check spread — ensures contrast stays at the target and does not spread to adjacent structures or show venous uptake
6. Anesthetic injection: 0.25-0.5 mL of local anesthetic per nerve (lumbar); 0.25 mL per level (cervical typical); 0.2 mL per target (cervical TON/C7)
   • First block: Typically bupivacaine 0.5%
   • Confirmatory block: Lidocaine 2% (on a separate day)
7. Multiple levels: Repeat for each medial branch nerve that must be blocked
8. Post-procedure assessment: Evaluate the patient for 20-60 minutes for degree of pain relief and response to previously painful activity; provide a pain diary

Controlled (Dual) Block Protocol

1. First MBB: Using one anesthetic (e.g., bupivacaine 0.5%)
2. Assessment: Patient must report >80% pain relief lasting an appropriate duration
3. Second MBB (confirmatory): On a separate day, using a different anesthetic (e.g., lidocaine 2%)
4. Concordant response: Relief duration must correspond to the pharmacology of the anesthetic — shorter with lidocaine, longer with bupivacaine
5. If both positive: Patient is a candidate for radiofrequency ablation