Harold J. Cordner and André M. Mansano

1. PROS OF OBLIQUE APPROACH

• Shorter needle track and less patient discomfort than posterior approach
• Patient in supine position, affords better comfort, communication, and airway access
• Easy visualization of lower levels

2. CONS OF OBLIQUE APPROACH

• Vital structures (spinal cord and vertebral artery) in needle trajectory
• Parallel placement of an RF cannula to the medial branch nerve is not possible, technique is less suitable for RF ablation (unless special needles are used)

3. EQUIPMENT AND MONITORING

• Standard ASA monitoring
• Fluoroscopy
• Sterile prep, and drape
• Skin local anesthesia prior to any needle larger than 25G (unless sedation is used)
• Procedure is not performed with a coaxial view
• CPR equipment and medications available 
• For diagnostic block
  • 22–25G, 2 inch (50 mm) – 3.5 inch (90 mm) needle, tip curved to facilitate steering. 0.3- 0.5  ml local anesthetic/level
  • Non-ionic contrast (optional)
• For RFA
  • 18–22G, 2 inch (50 mm)
  • 3.5 inch (90 mm) radiofrequency cannula: 5–10 mm active tip
  • Grounding pad – RF generator with capacity for unipolar and bipolar lesions
  • Local anesthetic

4. ANATOMY

• Prevalence studies, physical exam, and pain referral maps can be utilized to choose levels
• C2–3 and C5–6 levels are the most common causes of cervicogenic headache and neck pain, respectively
• At the C3 level, there is a superfcial medial branch (third occipital nerve) that is located in close proximity to the C2/3 facet joint and serves to innervate that joint as well as the suboccipital area
• The deep medial branch of C3 (which is analogous to the medial branches of C4, C5, and C6) courses along the waist of the corresponding articular pillars and supplies the adjacent vertebral segments (for instance, the C4 and C5 medial branches supply the zygapophyseal joint of C4/5)
• The C5 medial branch is located in the waist of the articular pillar of C5. The C3, C4, and C6 medial branches are located slightly above the waist of the corresponding articular pillars, and variations exist
• The C7 vertebra has a prominent transverse process (TP), and the location of the medial branch at this level is variable. It can be found as far caudal as the TP/superior articular process (SAP) junction and as far rostral as the apex of the C7 SA 

5. STRUCTURES TO KEEP IN MIND AND POSSIBLE COMPLICATIONS

• Vertebral artery (if needle is more anterior than appropriate target) → seizure, dissection, stroke
• Inadvertent intraarticular facet injection
• Inadvertent passage of needle though a facet joint  →  intrathecal, epidural medication administration, high spinal anesthesia, spinal cord injury, paralysis, death
• Injection of spinal nerve root → nerve damage, epidural, intrathecal injection
• Injection of a vascular structure that may be in contiguity with a radicular artery → spinal cord infarct
• Infection
• Bleeding
• Postprocedure pain
• Vasovagal reaction
• Allergic reaction

6. FLUOROSCOPY TECHNIQUE, TARGET LOCALIZATION

• Supine patient position
• C-arm in lateral view. In a true lateral, the articular pillars overlap and are clear and crisp. The facet joints above and below the level of interest must be crisp. The disc spaces must be clear. The anterior and posterior tubercles on each side should form a superimposed curvilinear line located in the superior posterior quadrant of the vertebral body shadow (Fig. 1a and b)
• A cranio-caudal or dorsoventral adjustment may be needed to get an optimal view of the articular pillar
• At this point, oblique the C-arm until the neural foramens are clearly visualized (Fig. 1a–c)
• The target point is the base of the superior articular process (SAP) at or just below the most inferior aspect of the intervertebral foramen 
• The skin entry point (Fig. 2a, b) is slightly posterior and caudal to the target