7.1 Fluoroscopic Spine Interventions

Fluoroscopic Spine Interventions

Fluoroscopically guided interventional spine procedures represent a core component of Physical Medicine & Rehabilitation (PM&R) practice for managing painful spinal disorders, including radiculopathy, facetogenic pain, and sacroiliac joint dysfunction. Fluoroscopic visualization ensures precise needle placement, target localization, and real-time contrast injection to verify proper epidural or intra-articular flow while preventing accidental intravascular, intrathecal, or soft tissue injection. High-resolution fluoroscopy combined with digital subtraction angiography (DSA) is essential when performing high-risk spinal interventions near major vascular structures.

Epidural Steroid Injections (ESIs)

Epidural steroid injections deliver potent anti-inflammatory corticosteroids directly to the epidural space surrounding inflamed spinal nerve roots and the dura mater. Corticosteroids inhibit phospholipase A2, reduce the synthesis of pro-inflammatory prostaglandins and leukotrienes, and suppress local edema and nociceptive C-fiber conduction. The three primary fluoroscopic approaches to the epidural space are transforaminal, interlaminar, and caudal.

Transforaminal Epidural Steroid Injection (TFESI)

The transforaminal approach introduces the needle into the neural foramen under oblique fluoroscopic guidance, positioning the needle tip in the target region (traditionally the "safe triangle" in the lumbar spine, bounded superiorly by the pedicle, laterally by the spinal nerve, and medially by the dural sac). This approach deposits medication directly into the anterior (ventral) epidural space where nerve root compression and disc herniation typically occur.

• Lumbar TFESI: Delivers medication with high target specificity. However, the lumbar neural foramen contains the radiculomedullary arteries, notably the artery of Adamkiewicz (great anterior radiculomedullary artery), which typically arises on the left side between T8 and L2. Accidental intravascular injection of particulate corticosteroids (e.g., triamcinolone, methylprednisolone) can cause embolic occlusion of the anterior spinal artery, resulting in catastrophic anterior spinal cord infarction and permanent paraplegia. Consequently, non-particulate steroids (dexamethasone) are strongly advocated as first-line agents for lumbar TFESI, and real-time contrast fluoroscopy or digital subtraction angiography (DSA) is mandatory prior to steroid injection.
• Cervical TFESI: Carries heightened vascular risks due to the proximity of the vertebral artery and deep cervical arteries. Inadvertent arterial injection of particulate steroids can cause embolic brainstem or cerebellar stroke. Current interventional guidelines mandate the exclusive use of non-particulate dexamethasone and strict contrast flow verification under DSA for cervical TFESI.

Interlaminar Epidural Steroid Injection (ILESI)

The interlaminar approach enters the dorsal epidural space between adjacent spinal laminae. The needle is advanced in the AP and oblique views using the loss-of-resistance (LOR) technique (to saline or air) as the needle pierces the ligamentum flavum.

• Lumbar ILESI: Provides broad, bilateral medication spread across multiple spinal segments. It is indicated for multi-level central spinal stenosis or bilateral lumbar radiculopathy. It does not deliver steroid directly to the ventral epidural space as effectively as a TFESI, but it carries a lower risk of direct radiculomedullary arterial injury.
• Cervical ILESI: Typically performed at the C7-T1 or C6-C7 level under contralateral oblique (CLO) or lateral fluoroscopic imaging. C7-T1 is chosen because it features the widest posterior epidural space and reduced risk of cord trauma compared to higher cervical levels. The ligamentum flavum may be non-fused in the midline in up to 10% of individuals, requiring meticulous LOR technique.

Caudal Epidural Steroid Injection

The caudal approach enters the caudal epidural space via the sacral hiatus, passing through the sacrococcygeal ligament into the sacral canal.

• Clinical Application: Caudal injections are particularly advantageous in patients with prior lumbar laminectomy or extensive spinal fusion hardware (post-laminectomy syndrome / failed back surgery syndrome) where the lumbar interlaminar space is obliterated by scar tissue. Contrast flow under fluoroscopy must demonstrate a characteristic "Christmas tree" spread along the sacral nerve roots and lower lumbar epidural space. High volume (10-20 mL) is often required to achieve adequate cephalad reach to the lower lumbar nerve roots.

Facet Joint Interventions & Medial Branch Blocks (MBBs)

The zygapophyseal (facet) joints are synovial joints formed by the inferior articular process of the superior vertebra and the superior articular process of the inferior vertebra. Facet joint arthropathy is a frequent source of axial back pain without radiculopathy, exacerbated by lumbar extension and rotation.

Facet Innervation & Dual Supply

Each facet joint receives dual innervation from the medial branches of the posterior primary rami of the spinal nerves. Specifically, a lumbar facet joint is innervated by the medial branch of the dorsal ramus at the same vertebral level and the medial branch from the level above.

• Example: The L4-L5 facet joint is innervated by the L3 medial branch (crossing the L4 transverse process) and the L4 medial branch (crossing the L5 transverse process). Therefore, complete denervation of the L4-L5 facet joint requires blocking or ablating both the L3 and L4 medial branches.
• L5 Dorsal Ramus: The L5-S1 facet joint is innervated by the L4 medial branch and the L5 dorsal ramus (which runs in the groove between the sacral ala and the S1 superior articular process).

Diagnostic Medial Branch Blocks (MBB) vs Radiofrequency Ablation (RFA)

Because physical examination and cross-sectional imaging (MRI/CT) cannot reliably identify facet pain generators, diagnostic medial branch blocks using small volumes (0.3-0.5 mL) of local anesthetic (e.g., lidocaine or bupivacaine) under fluoroscopy are required.

1. Dual Comparative Diagnostic Blocks: Guidelines mandate two concordant positive diagnostic MBBs (demonstrating ≥50% to ≥80% concordant pain relief during the duration of action of the local anesthetic) before proceeding to RFA. Dual blocks significantly reduce false-positive rates (which can exceed 30% with single blocks).
2. Radiofrequency Ablation (RFA): Thermal conventional RFA applies high-frequency alternating current to heat the nerve tissue to 80°C for 60 to 90 seconds, causing thermal coagulative necrosis of the medial branch. The RFA cannula must be placed parallel (not perpendicular) to the nerve course along the anatomical waist of the articular pillar (cervical) or the junction of the transverse process and superior articular process (lumbar). Successful RFA provides 6 to 12 months of pain relief until axonal regeneration occurs, at which point the procedure may be repeated.

Sacroiliac Joint (SIJ) Injections

The sacroiliac joint is a complex, diarthrodial synovial joint in its anterior lower one-third and a syndesmosis in its posterior upper two-thirds. SIJ pain accounts for 15-30% of axial low back pain cases and characteristically presents as pain below the L5 level, overlying the posterior superior iliac spine (PSIS) (Fortin finger test), with pain radiation to the buttocks and posterior thigh.

• Fluoroscopic SIJ Injection: The needle is directed into the inferior synovial portion of the posterior joint line under AP fluoroscopy with ipsilateral oblique rotation (10-20 degrees). Contrast confirmation of an intra-articular arthrogram pattern (outlining the joint capsule without extra-articular extravasation) is essential prior to injecting a corticosteroid and local anesthetic mixture.
• SIJ Radiofrequency Neurotomy: For patients with confirmed SIJ pain who obtain temporary relief from intra-articular injections, lateral branch RFA (ablating the L5 dorsal ramus and S1, S2, and S3 lateral branches) can yield long-term therapeutic relief.