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Complications of Thoracic Facet Blocks and Ablations

Robert Chow MD¹, Melanie G. Wood MD¹, and Milan P. Stojanovic MD FIPP²

¹ Yale University School of Medicine, New Haven, CT, USA
² Harvard Medical School, Boston, MA, USA

Introduction

While chronic thoracic pain is less common in comparison to low back pain, it is estimated that 34–42% of patients with upper or mid-back pain have symptoms originating from the thoracic facet joints (TFJ) [1]. Routine diagnostic tests such as physical exam, X-rays, computed tomography (CT) scans, and magnetic resonance imaging (MRI) lack adequate specificity for the diagnosis of TFJ pain. However, intra-articular facet joint blocks and especially medial branch blocks have the best diagnostic and prognostic validity for the diagnosis of thoracic facet pain [2]. Patients who experience short-term pain relief from medial branch blocks may benefit long-term from radiofrequency ablation (RFA) with subsequent pain reduction and improvement in function [3]. While these procedures are similar to lumbar procedures, it is important to emphasize the significant differences in anatomy between the lumbar and thoracic regions.

Anatomy

The dorsal ramus branches of the spinal nerve exit from the intervertebral foramen. As the dorsal ramus runs posteriorly, it divides into medial and lateral branches. These two branches innervate the surrounding skin and muscles. The medial branch also innervates the medial and superior aspects of the facet joint as well as the lateral and inferior aspects of the adjacent vertebra. Each facet joint is innervated by branches of both adjacent dorsal rami (Figure 26.1).

**Figure 26.1** Thoracic medial branches by level – note how the medial branches are suspended in intra-transverse space [4].

At the lumbar levels, the medial branches typically traverse at the junction between the superior articular process (SAP) and the transverse process (TP). However, none of the thoracic medial branches were found to be at this junction [4] and its course changes depending on the level. In the upper and lower levels (T1–3 and T9–10), the medial branches course dorsally and inferiorly, while suspended in the intertransverse space, and then travel to the superolateral edge of the transverse processes to the posterior compartment by running caudally across the transverse process (Figure 26.1).

At the mid-thoracic levels (T4–8), the medial branches have widely variable courses, even between opposite sides of the same person. Often, the nerve is suspended in the intervertebral space without bony contact. A recent cadaveric study described facet innervation directly from the posterior ramus and not from the medial branch with articular branches running closer to the intervertebral foramina with only 39% of articular branches making osseous contact [5].

At T11 and T12 levels, the medial branch courses differ. As T12 has a short transverse process, the T11 medial branch passes close to the root of the superior articular process of T12. The T12 medial branch has a similar course to the lumbar levels [4].

Indications

Medial branch blocks, facet joint injection
- –Thoracic pain, potentially originating from the facet joints.
RFA
- –Patients who experience short-term benefit from diagnostic blocks.

Contraindications

Systemic or local infection
Pneumothorax
Severe asthma or COPD (relative contraindication)
Recent myocardial infarction
Patient refusal
Thoracic radicular pain conditions.

Technique

With the patient in the prone position (Figure 26.2), the vertebral levels are identified under C-arm fluoroscopic guidance.

**Figure 26.2** Patient is placed in prone position on fluoroscopic table.

Facet Joint Injection

The target level is identified using the posteroanterior C-arm view, and then repositioned to the oblique view to better visualize the targeted facet joints.

A 22–25G spinal needle is introduced into the skin and angled caudally at a 45–60° angle. The needle is advanced to target the TFJ space until bony contact is made. The needle is then redirected to pierce the joint capsule. Placement is confirmed with the injection of 0.3 ml of contrast, showing spread from the inferior recess to superior recess. If irregular contrast spread is seen, the needle should be repositioned. Following appropriate contrast spread, 0.5 ml of 0.5% bupivacaine is then injected into the joint.

Medial Branch Block (MBB)

The target level is identified using the posteroanterior C-arm view, and then repositioned to the oblique view to better visualize the facet joint anatomy.

The correct vertebral level and the course of the medial branch should be identified, as the course of medial branches varies by level.

A 22–25G spinal needle is advanced to the target medial branch. For T1–4 and T9–10, the needle is advanced to the superolateral edge of the thoracic transverse process to the point where the SAP meets the periosteum of the TP. For T5–T8, a needle is placed to make contact with the posterior rib at the same depth as the transverse process, as cadaveric studies have shown the medial branch passes superficial to the rib at the depth of the corresponding transverse process [4]. At T11–12, the needle is advanced to the junction of the SAP and transverse process. Blocking the medial branch must be done on two consecutive levels for proper coverage. Once the accurate needle position is verified, 0.25–0.5 mL of 0.5% bupivacaine is then injected.

Radiofrequency Ablation (RFA)

The RF cannulas are positioned at a similar location as described in the MBB section. The RF cannulas should be positioned parallel to the target medial branch, with 10 degrees of caudal tilt and 10 degrees of contralateral oblique angulation. An electrode probe is placed into cannula; after motor and (if indicated) sensory testing, the nerves are ablated at 80°C for 90 seconds.

Complications

Most complications from thoracic interventions stem from improper placement of the needle, or improper injection of local anesthetic. Less damaging complications include generalized trauma to the surrounding area with hematoma formation. The complications may be categorized as: