Selective Nerve Root Blocks in Spine Surgery

Courtesy: Rishi Mugesh Kanna, Consultant Spine Surgeon, Ganga Hospital, Coimbatore, India

Spinal Injections

• Spinal injections are defined as injections performed in and around the vertebral column, spinal cord, and nerve roots.

• They may involve one or more of the following agents:

  • Local anesthetics for diagnostic nerve blocks

  • Steroids for epidural steroid injections

  • Contrast dye for discography

• Spinal injections may be:

  • Diagnostic

  • Therapeutic

  • Both diagnostic and therapeutic

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Classification of Spinal Injections

Diagnostic Injections

• Discography for evaluation of axial back pain

• Facet joint injections

• Diagnostic nerve root blocks

Diagnostic and Therapeutic Injections

• Epidural steroid injections:

  • Transforaminal

  • Interlaminar

  • Caudal

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Transforaminal Epidural Steroid Injection

(Selective Nerve Root Block)

• Used for:

  • Unilateral radiculopathy (preferred)

  • Bilateral radiculopathy

• Indications include:

  • Lumbar disc prolapse

  • Lumbar canal stenosis

  • Facet joint cyst

  • Spondylolisthesis

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Pathophysiology of Lumbar Radiculopathy

• Radiculopathy occurs due to:

  • Mechanical compression of the nerve root

  • Chemical inflammation around the nerve root

• Radicular pain is primarily produced by inflammation

• Mechanisms include:

  • Autoimmune response to disc material in acute herniated nucleus pulposus

  • Venous congestion and ischemia in chronic disc prolapse and foraminal stenosis

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Principle of Steroid Use

• Steroids reduce acute inflammation around the nerve root

• This helps break the pain cycle and provides symptom relief

• Mechanisms of action include:

  • Suppression of nociceptive transmission in unmyelinated C fibers

  • Inhibition of phospholipase A2 and inflammatory mediators

  • Reduction of capillary permeability

  • Membrane stabilizing effect

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Transforaminal Epidural Steroid Injection: Key Features

• Widely accepted standard of care in many countries

• Day-care procedure

• Provides immediate analgesic effect

• Cost-effective

• Performed under local anesthesia

• Patient positioned prone

• Fluoroscopy guidance is essential

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Needle Placement and Safe Triangle Concept

• Needle is placed into the neuroforamen toward the safe triangle

• Boundaries of the safe triangle:

  • Superior border: Inferior margin of the pedicle

  • Medial border: Lateral margin of the pedicle

  • Hypotenuse: Oblique line passing inferolaterally from the inferomedial corner of the pedicle

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Steps of Transforaminal Epidural Injection

1. Obtain an oblique fluoroscopic view to identify the scotty dog appearance.

2. Infiltrate the skin and deeper tissues with local anesthetic.

3. Advance a 22 gauge spinal needle toward the safe triangle.

4. Confirm needle position on lateral view with the tip located in the neural foramen below the pedicle.

5. Inject contrast dye, such as iohexol, to confirm nerve root outline.

6. Inject the final drug mixture around the nerve root:

   • Triamcinolone 80 milligrams

   • Bupivacaine 0.5 percent, 2 milliliters

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Post-Injection Protocol

• Patient is mobilized within 30 minutes

• Discharge is possible within 2 hours

• Approximately 5 to 10 percent of patients may develop:

  • Temporary numbness

  • Mild weakness

• These symptoms usually resolve within 4 hours

• Return to normal work is permitted from the next day

• Clinical review at 6 weeks

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Selection of Nerve Root for Injection

• Applicable from lumbar nerve roots L2 to L5

• For posterolateral disc prolapse:

  • Target the traversing nerve root

  • Example: L5 nerve root in L4–L5 disc prolapse

• For foraminal or far-lateral disc prolapse:

  • Target the exiting nerve root

  • Example: L4 nerve root in L4–L5 disc prolapse

• For posterocentral disc prolapse:

  • Target the traversing nerve root on the more symptomatic side

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Factors for Successful Transforaminal Injection

• Accurate clinical and magnetic resonance imaging correlation

• Correct identification of involved nerve root

• Correlation of magnetic resonance imaging with fluoroscopy, especially in lumbosacral transitional vertebrae

• Precise needle placement

• Clear radiculogram

• Reproduction of typical radicular pain during contrast injection

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Frequency of Injections

• In appropriately selected patients, success rate exceeds 75 percent

• If pain recurs after 6 weeks, repeat injection may be considered

• Conventionally, no more than 3 injections are recommended

• If no relief is achieved within 1 week, or pain recurs within 6 weeks, surgical options should be discussed

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Interlaminar Epidural Steroid Injection

• Most commonly performed by anesthesiologists

• Injection given through the interlaminar space, usually at L3–L4 or L4–L5

• Midline approach is used

• Loss of resistance technique employed

• Fluoroscopy is usually not used

• Drug spread is less targeted compared to transforaminal injection

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Caudal Epidural Steroid Injection

• Injection administered through the sacral hiatus

• Sacral hiatus is a midline defect between the S4 and S5 laminae

• Thecal sac typically ends at the S2 level

• Lowest risk of accidental dural puncture

• Drug spread is diffuse and nonspecific

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Comparison of Epidural Injection Techniques

• Transforaminal injection:

  • Highly target-specific

  • Small, concentrated drug volume

  • Very high efficacy

  • Requires greater technical skill

  • Ideal for unilateral radiculopathy

• Interlaminar injection:

  • Moderately specific

  • Larger and more diluted drug volume

  • Moderate efficacy

  • Suitable for unilateral or bilateral radicular pain

• Caudal injection:

  • Least specific

  • Largest and most diluted drug volume

  • Lower efficacy

  • Easiest to perform

  • Useful for bilateral or nonspecific symptoms

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Outcomes

• Transforaminal injections show superior outcomes compared to interlaminar and caudal techniques

• Best suited for:

  • Acute

  • Single-level

  • Unilateral radiculopathy

• Approximately 70 to 80 percent of patients show good pain relief at 2 weeks

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Poor Prognostic Factors

• Predominant sensory symptoms

• Higher Oswestry Disability Index score

• Non-manual occupation

• Presence of lumbosacral transitional vertebra

• Diffuse or splash pattern on radiculogram

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Take-Home Messages

• Spinal injections play both diagnostic and therapeutic roles

• Radicular pain is best treated with transforaminal epidural injection

• Selective nerve root blocks are highly specific and target-oriented

• Best results are seen in acute and unilateral radiculopathy

• Technique has a short learning curve, low complication rate, and good outcomes