Comparing Three Epidural Steroid Injection Approaches for Lumbar Radicular Pain

Epidural Contrast Patterns as Predictors of Radicular Pain Relief: A Three-Arm Randomized Trial Comparing High-Volume Interlaminar, Low-Volume Interlaminar, and Transforaminal Injections

This study will compare three fluoroscopy-guided epidural steroid injection approaches for adults with unilateral lumbosacral radicular pain caused by lumbar disc herniation. The study will evaluate whether the pattern of contrast spread in the epidural space predicts meaningful pain relief.

Ninety-nine participants will be randomly assigned in equal numbers to receive one of three treatments: high-volume parasagittal interlaminar injection, low-volume parasagittal interlaminar injection, or transforaminal epidural steroid injection. Participants will not be told which injection approach they receive. Pain and disability will be assessed before treatment and at 2 weeks, 1 month, 3 months, and 6 months after injection. The main outcome is the proportion of participants with clinically meaningful improvement in pain at 3 months.

Lumbar disc herniation may cause lumbosacral radicular pain through nerve-root compression and inflammation. Fluoroscopy-guided epidural steroid injections are commonly used when symptoms persist despite conservative treatment. Parasagittal interlaminar (PIL) and transforaminal epidural steroid injection (TFESI) approaches may produce different patterns of contrast distribution within the epidural space. It remains unclear whether contrast spread pattern independently predicts clinical response, apart from injection approach and injectate volume.

This prospective, three-arm randomized clinical trial will enroll adults with unilateral lumbosacral radicular pain and magnetic resonance imaging-confirmed lumbar disc herniation. Participants will be allocated in a 1:1:1 ratio to high-volume PIL injection (10 mL), low-volume PIL injection (7 mL), or TFESI (3 mL). Before administration of the therapeutic injectate, 2 mL of non-ionic iodinated contrast medium will be injected under real-time fluoroscopy to confirm epidural placement, exclude intravascular or intrathecal injection, and document contrast distribution.

Blinded assessors will classify contrast spread according to ventral epidural spread, laterality, foraminal or nerve-root spread, epidural distribution pattern, and cephalocaudal extent. Dynamic fluoroscopic assessment will measure time to first ventral opacification. Participants, radiographic assessors, and outcome assessors will be blinded to treatment allocation where feasible; the procedural physician cannot be blinded because of the procedural differences.

The study will assess whether contrast spread variables independently predict responder status at 3 months, defined as a reduction of at least 2 points or 30% from baseline in Numerical Rating Scale pain score. Additional outcomes include changes in pain intensity and Oswestry Disability Index scores, procedural efficiency, duration of pain relief, and responder status during follow-up through 6 months.

Inclusion Criteria:

• Age 18 to 65 years.
• Unilateral lumbosacral radicular pain consistent with a dermatomal distribution.
• Magnetic resonance imaging-confirmed lumbar disc herniation (bulge, protrusion, or extrusion) at the corresponding clinical level.
• Persistent symptoms despite at least 6 weeks of conservative management, including analgesics and physiotherapy.
• Baseline Numerical Rating Scale pain score of 4 or greater.
• American Society of Anesthesiologists physical status I to III.
• Ability to understand and complete outcome assessments.
• Written informed consent provided.

Exclusion Criteria:

• Previous lumbar spine surgery or failed back surgery syndrome.
• Red-flag signs, including foot drop, urinary incontinence, or cauda equina syndrome.
• Bilateral radicular symptoms or central canal stenosis requiring surgical intervention.
• Coagulopathy or ongoing anticoagulant therapy.
• Local or systemic infection or hepatic dysfunction.
• Known allergy to contrast medium, local anesthetics, or corticosteroids.
• Pregnancy.
• Severe renal impairment contraindicating contrast use.
• Chronic opioid use, defined as daily opioid use for more than 3 months before enrollment.
• Uncontrolled systemic disease, including unstable diabetes or severe cardiopulmonary disease.
• Inability to comply with follow-up.