Induced lumbosacral radicular symptom referral patterns: a descriptive study

Key points

1. 01Buttock and posterior thigh pain were the most common referral zones for all levels tested (L3, L4, L5, S1)
2. 0287 of 125 injections provoked referred symptoms; 38 did not and were excluded
3. 03L5 most often referred to buttock (62%), posterior thigh (59%), and posterior calf (50%)
4. 04S1 did not refer to the anterior thigh or anterior lower leg in any case
5. 05Classic dermatome maps could not reliably predict which level was causing the symptoms

How it was conducted

Design

Observational descriptive study

Setting

Outpatient interventional spine practice

Participants

71 consecutive patients with lumbosacral radicular pain undergoing fluoroscopically guided transforaminal epidural injections

Injections performed

125 injections at L1, L2, L3, L4, L5, and S1 levels

Procedure

Patients drew provoked symptom location on anatomic diagrams after needle positioning, contrast injection (up to 0.5 ml), and 1% lidocaine test dose (up to 1.0 ml)

Primary outcome

Composite nerve-root-level symptom referral pattern maps with proportions and 95% confidence intervals

What they found

• 87 of 125 injections (69.6%) provoked referred symptoms included in analysis; 38 injections excluded for no provoked symptoms
• L3 nerve root (n=11): buttock 45% (95% CI 9.5-57.2%), posterior thigh 36% (95% CI 4.3-49.0%)
• L4 nerve root (n=28): buttock 43% (95% CI 24.5-61.2%), anterior thigh 29% (95% CI 11.8-45.3%), posterior thigh 25% (95% CI 9.0-41.0%), posterior calf 18% (95% CI 3.7-32.0%)
• L5 nerve root (n=34): buttock 62% (95% CI 45.4-78.1%), posterior thigh 59% (95% CI 42.3-75.4%), posterior calf 50% (95% CI 33.2-66.8%), lateral lower leg 24% (95% CI 9.3-37.8%)
• S1 nerve root (n=11): buttock 64% (95% CI 35.2-92.1%), posterior calf 45% (95% CI 16.7-74.9%), posterior thigh 36% (95% CI 7.9-64.8%); no referral to anterior thigh or anterior lower leg
• Most common pattern across L3 to S1 was buttock, posterior thigh, and posterior calf

Limitations

• Small sample size, especially at upper lumbar levels (L1 and L2 could not be analyzed); wide confidence intervals throughout
• Possible non-selectivity: 1.5 ml injectate volume spreads to adjacent levels in 57-67% of cases, so symptoms may reflect multi-level rather than single-level root irritation
• Qualitative pain diagram method relies on patient drawing accuracy and may under- or over-represent true referral zones
• Left and right sided injections were combined, potentially masking laterality differences

Why it matters

For patients

Buttock and leg pain along the back of the thigh or calf do not pinpoint which nerve root is involved, so imaging and clinical examination are needed to plan any injection treatment.

For clinicians

Symptom distribution alone is unreliable for level-specific diagnosis; MRI correlation is essential before targeting a specific lumbosacral level with a transforaminal epidural injection.

For readers

This study provides the first composite referral maps from chemically and mechanically provoked lumbosacral nerve roots in humans, showing broader and more overlapping patterns than classical dermatome maps suggest.