REHAB · EP 03 · PAIN
Before You Listen
Episode Setup
- Topic in one line: the procedural toolkit of modern physiatric pain medicine, anchored in the three epidural steroid injection (ESI) approaches (interlaminar, transforaminal, caudal), the particulate-versus-non-particulate steroid rule for cervical transforaminal injections, facet joint pain diagnostic algorithm (medial branch block to radiofrequency ablation (RFA)), sacroiliac joint procedures, vertebroplasty and kyphoplasty, neuromodulation (spinal cord stimulation (SCS), dorsal root ganglion (DRG) stimulation, peripheral nerve stimulation), intrathecal drug delivery (morphine and ziconotide), botulinum toxin for chronic migraine and myofascial pain, ketamine infusion for refractory complex regional pain syndrome (CRPS), and the radiation safety principles (inverse square law, As Low As Reasonably Achievable (ALARA)) that govern fluoroscopic procedures.
- Prerequisites: REHAB-01 (gate control theory, dorsal horn anatomy, opioid receptors and pharmacology) and REHAB-02 (CRPS Budapest criteria, sympathetic block anatomy by region, cancer pain ladder).
- Runtime: 1 hour 10 minutes.
Vignette. A 64-year-old woman with osteoporosis is referred for axial low back pain following a fall onto her buttocks 5 days ago. She rates her pain 9 out of 10, worse with sitting and weight bearing, with no radicular symptoms. She has no incontinence and no lower-extremity weakness. Magnetic resonance imaging (MRI) of the lumbar spine shows an acute T2-hyperintense fracture at L1 with anterior wedging of approximately 30 percent and bone marrow edema; there is no retropulsion, no spinal canal compromise, and no posterior wall involvement. She is also being evaluated separately for chronic axial low back pain at L4-L5 and L5-S1 with greater than 80 percent relief from each of two medial branch blocks performed on separate days using lidocaine and bupivacaine. Vitamin D is 18 ng/mL.
What procedure addresses the acute fracture, what is the anatomic rule for the radiofrequency ablation that follows the dual comparative blocks for her chronic pain, what nerve targets are required to denervate the L4-L5 and L5-S1 facet joints, and what radiation safety principle governs operator positioning during the fluoroscopic portions of these procedures?
(Answer at the end of this chapter)
Section 1: Epidural Steroid Injections — Three Approaches and the Particulate Steroid Rule
Bottom line: ESIs treat radicular pain from disc herniation or foraminal stenosis through three approaches: interlaminar (loss-of-resistance through the ligamentum flavum with a Tuohy needle, posterior epidural space, lower vascular risk), transforaminal (fluoroscopy-guided needle placement in the safe triangle of the Scotty dog view at the inferior pedicle, anterior epidural space, most precise but highest vascular risk), and caudal (through the sacral hiatus between the sacral cornua, lowest dural puncture risk, requires larger volume); the absolute rule for cervical transforaminal ESI is to use non-particulate dexamethasone or betamethasone sodium phosphate because particulate methylprednisolone or triamcinolone can embolize into the vertebral artery or radicular feeders to the anterior spinal artery and cause cord infarction or posterior circulation stroke; epinephrine in lumbar ESI is generally avoided to preserve the test for vascular uptake.
The primary indication for an epidural steroid injection (ESI) is radicular pain from disc herniation or foraminal stenosis, where steroid reduces inflammation around the compressed nerve root. Three anatomic approaches exist, each with characteristic indications, technique, and risks.
The interlaminar approach is the most traditional. The needle traverses the skin, subcutaneous tissue, supraspinous and interspinous ligaments, and the ligamentum flavum into the posterior epidural space. The hallmark technical maneuver is loss of resistance: a glass syringe filled with saline or air is attached to a Tuohy needle, and continuous gentle pressure on the plunger is applied while advancing. As long as the needle tip is embedded in dense ligamentum flavum, the plunger does not move; once the tip penetrates the ligamentum flavum into the epidural space, resistance disappears and the plunger glides forward freely. This loss confirms entry. The interlaminar approach delivers medication to the posterior epidural space, requiring diffusion anteriorly to reach the nerve root. It is technically simpler than transforaminal injection and carries lower risk of vascular injection.
The transforaminal approach is fluoroscopy-guided and delivers medication directly to the anterior epidural space at the targeted nerve root. The needle enters through the neural foramen, placing the steroid directly at the disc-nerve interface. The fluoroscopic landmark is the Scotty dog view, an oblique view of the lumbar spine in which the posterior elements form a profile resembling a Scottish terrier: the pedicle is the eye, the transverse process is the nose, the superior articular process is the ear, the pars interarticularis is the neck, the inferior articular process is the front leg, and the lamina is the body. A pars fracture (spondylolysis) appears as a collar across the dog’s neck. The needle is placed in the safe triangle: the region bounded by the inferior border of the pedicle above, the lateral border of the vertebral body medially, and the exiting nerve root laterally and below. An alternative target is the Kambin triangle, the posterolateral safe zone of the foramen bounded by the exiting nerve root superiorly, the traversing nerve root medially, and the caudal endplate inferiorly.
Figure 3.1 — ESI three approaches diagram: interlaminar (posterior epidural via Tuohy + loss of resistance), transforaminal (safe triangle in Scotty dog view, anterior epidural), caudal (through sacral hiatus between cornua). Open-source spinal anatomy illustration; license CC BY or CC BY-SA only.
Figure 3.2 — C-arm fluoroscopic AP and lateral images of a lumbar transforaminal epidural needle placement: needle in the safe triangle on the AP view at the inferior border of the pedicle, with corresponding lateral view confirming anterior epidural needle tip position and contrast spread along the exiting nerve root. Open-source fluoroscopic image from Wikimedia/PMC CC BY preferred. Anchors the abstract Scotty-dog landmark in actual procedural imagery and reinforces the contrast-confirmation step before steroid delivery.
The critical safety distinction for cervical transforaminal ESI is steroid choice. Particulate steroids (methylprednisolone / Depo-Medrol, triamcinolone / Kenalog) are crystalline suspensions whose particles can embolize if inadvertently injected into a radicular artery. In the cervical spine, the vertebral artery and radicular feeders to the anterior spinal artery course through or adjacent to the neural foramen near the needle path. Particulate steroid embolization can produce catastrophic spinal cord infarction, posterior circulation stroke, or death. Non-particulate dexamethasone is required for cervical transforaminal ESI (a true solution, not a suspension); betamethasone sodium phosphate (Celestone Soluspan) is also non-particulate. This rule is absolute. In the lumbar spine the catastrophic risk is lower (the artery of Adamkiewicz typically arises on the left between T9 and T12), but many practitioners now use non-particulate agents universally.
The caudal approach enters the epidural space through the sacral hiatus, the opening at the inferior end of the sacrum where the laminae of S5 are absent. The hiatus is identified by palpating the sacral cornua flanking it. The needle is directed superiorly at approximately 45 degrees through the sacrococcygeal ligament into the caudal epidural space. The primary advantage is the lowest risk of dural puncture because the thecal sac typically terminates at S2, well above the hiatus entry point, which makes the caudal approach the safest option in patients on anticoagulation or at high spinal headache risk. The disadvantages are the larger required volume (often 10 to 20 mL) and less precise delivery, since medication must travel upward through the epidural space.
High Yield — ESIs
- Interlaminar: Tuohy needle through ligamentum flavum, loss of resistance = entry; posterior epidural space; lowest vascular risk.
- Transforaminal: fluoroscopy-guided, safe triangle of Scotty dog view (pedicle = eye); most precise; highest vascular risk.
- Caudal: through sacral hiatus between cornua; lowest dural puncture risk; requires larger volume.
- Cervical transforaminal ESI: must use non-particulate dexamethasone (or betamethasone sodium phosphate). Particulate methylprednisolone / triamcinolone risk vertebral artery embolization → spinal cord infarction or stroke. Absolute rule.
For a cervical transforaminal epidural, you always, always use non-particulate dexamethasone, or betamethasone sodium phosphate. Because dexamethasone is a true solution. There are no particles to clump together and block an artery. It just washes right through the vascular system.
— REHAB-03-b podcast, ~1:47