Interlaminar & Caudal Epidural Steroid Injections

Interlaminar Epidural Technique

The interlaminar approach enters the epidural space between the laminae of adjacent vertebrae, typically using a loss-of-resistance technique combined with fluoroscopic guidance.

Step-by-Step Interlaminar Approach

1. Patient positioning: Prone on fluoroscopy table; lateral decubitus may be used for cervical
2. Level identification: AP fluoroscopy to identify the target interlaminar window
3. Approach selection: Paramedian approach is often preferred over midline in the lumbar spine to avoid the interspinous ligament
4. Needle: 18-20 gauge Tuohy needle (for catheter capability) or 20-22 gauge spinal needle for single-shot
5. Advancement: Using intermittent fluoroscopy, advance the needle through the skin, subcutaneous tissue, supraspinous/interspinous ligament, and ligamentum flavum
6. Loss of resistance: Use LOR technique with saline or air to identify entry into the epidural space
7. Fluoroscopic confirmation: Lateral view to confirm needle depth — the tip should be at or just past the ligamentum flavum
8. Contrast injection: 1-2 mL of non-ionic contrast under real-time fluoroscopy to confirm epidural spread pattern in at least two planes (AP plus CLO or lateral)
9. Steroid injection: Typical total volume of 2-4 mL (per IPSIS) including steroid and diluent. Particulate steroids are acceptable for interlaminar approaches because there is no direct arterial communication between the dorsal epidural space and the spinal cord. Maximum dose: 40 mg methylprednisolone or equivalent per injection.

Contralateral Oblique (CLO) View — per IPSIS

The IPSIS Technical Manual identifies the CLO view as superior to the lateral view for interlaminar epidural access:

• The CLO view is obtained by positioning the X-ray detector contralateral to the needle tip, projecting the X-ray beam parallel to the target-side lamina
• Optimal CLO angle is approximately 45-60 degrees from AP, varying by spinal segment
• The ventral interlaminar line (VILL) connects the anterior margins of consecutive laminae and represents the earliest expected location of loss of resistance
• CLO provides better needle tip visualization, more consistent epidural space identification, and ability to redirect after a false LOR compared to lateral view
• If the needle advances 1-2 mm past the VILL without LOR, check additional views and inject a small amount of contrast to confirm position

LOR Technique Details — per IPSIS

• Continuous pressure: Maintain constant pressure on syringe plunger while slowly advancing through the ligamentum flavum — sudden LOR signals epidural entry
• Ballottement: Alternatively, repeatedly tap the plunger while advancing in 1-mm increments
• Visual feedback: A sudden drop in the saline meniscus provides additional confirmation
• Critical limitation: LOR is complementary to imaging and must never be used alone. False LOR can occur in the space of Okada or through midline ligamentum flavum gaps. Contrast injection is mandatory to confirm placement.
• Pneumocephalus risk: If air is used for LOR, inject only minimal amounts to reduce the risk of symptomatic pneumocephalus

Caudal Epidural Technique

The caudal approach enters the epidural space through the sacral hiatus, well below the termination of the thecal sac.

1. Patient positioning: Prone with a pillow under the hips. Slight abduction of the legs with toes rotated inward helps relax the gluteal muscles.
2. Landmark identification: Palpate the sacral cornua — the sacral hiatus has an inverted U or V shape between them. Imagine an equilateral triangle using the posterior iliac spines as two points; the third point approximates the sacral hiatus location.
3. Fluoroscopy for difficult anatomy: If cornua cannot be palpated, a 45-55 degree caudal fluoroscopic tilt may help align ventral and dorsal sacral aspects to visualize the hiatus.
4. Needle insertion: 22-25G spinal needle for single-shot (1.5-3.5 inch) or 16-20G non-shearing introducer needle (Coude or Tuohy) for catheter placement. Advance through subcutaneous tissue and the posterior sacrococcygeal ligament (PSL) into the sacral canal. Contact with the S4 or S5 vertebral body will be evident.
5. Fluoroscopic confirmation: Lateral view to confirm the needle is within the sacral canal — not subcutaneous or presacral. Use intermittent AP imaging to confirm midline positioning.
6. Critical depth limit: Do not advance the needle beyond the S2-3 level, as the thecal sac typically terminates at S2. If thecal sac termination is unknown, do not advance beyond S3 before injecting contrast to verify epidural distribution. In patients with transitional lumbosacral anatomy, the thecal sac may terminate as low as S3.
7. Contrast injection: Inject under lateral real-time fluoroscopy, then AP view to assess laterality and cephalad flow. Confirm absence of vascular uptake or excessive flow through ventral sacral foramina.
8. Volume: Typically 5-15 mL total injectate (per IPSIS). Approximately 10 mL generally reaches lower lumbar levels.

Catheter Placement Option (per IPSIS)

When more targeted delivery is desired with lower volumes:

• A catheter is inserted through a non-shearing introducer needle (polished Coude or Tuohy)
• The catheter is observed ascending the caudal epidural space under lateral fluoroscopy
• The catheter may be steered toward the symptomatic side by rotating it
• When a catheter is used, the volume of injectate should be reduced to maintain high medication concentration at the target

Safety Profile of Caudal Approach

• Lowest risk of dural puncture: The sacral hiatus is well below the dural sac termination (typically S2)
• No risk of cord injury: The conus medullaris ends at L1-L2
• Failure rate: Approximately 5-10% due to sacral anatomical variations (absent sacral hiatus, calcified sacrococcygeal ligament, sacral agenesis)
• Unique infection risk (per IPSIS): The intragluteal area is a potential nidus for infection — evaluate for intertrigo or pilonidal cyst. Aseptic skin preparation is paramount.
• Intraosseous injection: A spinal needle may penetrate the sacral body cortex, producing a patchy contrast accumulation deep to the sacral canal on lateral view — withdraw and reposition if seen.