What is the role of a caudal epidural block with bilateral Posterior Superior Iliac Spine (PSIS) block in managing severe lower back and buttock pain?

Caudal Epidural Block with Bilateral PSIS Block for Severe Lower Back and Buttock Pain

Direct Answer

Caudal epidural steroid injection is an appropriate treatment option for chronic low back pain with radiculopathy, providing Level I evidence for short- and long-term relief, but there is no established role for combining it with bilateral PSIS (posterior superior iliac spine) blocks in standard clinical practice. 1

Evidence for Caudal Epidural Injections

Indications and Effectiveness

• Caudal epidural injections demonstrate Level I evidence for managing chronic low back and lower extremity pain secondary to lumbar disc herniation and/or radiculopathy, with both short-term (up to 6 months) and long-term (≥6 months) relief. 1

• For discogenic pain without disc herniation or radiculopathy, caudal epidural injections also show Level I evidence for effectiveness. 1

• Level II-1 or II-2 evidence supports caudal epidural injections for post-lumbar laminectomy syndrome and spinal stenosis. 1

• Caudal epidural injections provide faster and better improvement compared to NSAIDs in patients with subacute or chronic low back pain accompanied by radicular pain, with statistically significant differences in pain scores and straight leg raising tests at 15 days and 1 month. 2

Technical Considerations

• The volume injected is critical for effectiveness—10 ml is suitable and effective for treating lumbar spinal stenosis symptoms without side effects, providing pain reduction of over 50% at three-month follow-up. 3

• Ultrasound-guided caudal epidural injections have success rates of 96.9-100% and allow color Doppler confirmation that the drug solution reaches the lumbosacral region. 3

• Fluoroscopic guidance should be used for epidural injections to ensure proper needle placement and reduce risk of complications. 4, 5

Treatment Protocol

• Patients should have failed at least 4-6 weeks of conservative therapy including physical therapy, NSAIDs, and activity modification before considering caudal epidural injections. 4, 5

• MRI evidence of pathology such as nerve root compression must correlate with clinical symptoms (radicular pain radiating below the knee) to justify caudal epidural injection. 4, 5

• Caudal epidural injections must be part of a comprehensive multimodal pain management program including physical therapy, patient education, psychosocial support, and oral medications—not a standalone treatment. 4, 6

Medication Composition

• Standard caudal epidural injection includes local anesthetic (lidocaine or levobupivacaine), corticosteroid (methylprednisolone 40 mg or triamcinolone 40 mg), and physiological saline solution. 3, 7

• Repeat therapeutic injection is appropriate only if the initial injection resulted in at least 50% pain relief lasting at least 2 months. 5, 6

Lack of Evidence for PSIS Blocks

Critical Gap in Literature

• The provided evidence contains no guideline or research support for bilateral PSIS (posterior superior iliac spine) blocks as a treatment modality for low back pain. The literature focuses exclusively on epidural injections (caudal, interlaminar, transforaminal), facet injections, and trigger point injections. 8

• PSIS blocks are not mentioned in any major pain management guidelines including those from the American Society of Anesthesiologists, American College of Physicians, or Journal of Neurosurgery spine guidelines. 8, 4, 5, 6

Alternative Diagnostic Consideration

• If the patient has positive sacroiliac joint provocation tests (3 of 6 tests positive), diagnostic sacroiliac joint injection should be considered rather than PSIS blocks. 4 The PSIS serves as an anatomical landmark for sacroiliac joint injections, but "PSIS block" is not a standard interventional pain procedure.

Safety Considerations and Complications

Neurologic Risks

• Caudal epidural anesthesia may cause spinal block of varying magnitude, hypotension secondary to spinal block, urinary retention, persistent anesthesia, paresthesia, weakness, paralysis of the lower extremities, and loss of sphincter control—all of which may have slow, incomplete, or no recovery. 9

• Unintentional penetration of the subarachnoid space during caudal block can result in high spinal block characterized by paralysis of the legs, loss of consciousness, respiratory paralysis, and bradycardia. 9

Cardiovascular and Systemic Risks

• High doses or unintentional intravascular injection may lead to myocardial depression, decreased cardiac output, heart block, hypotension, bradycardia, ventricular arrhythmias including ventricular tachycardia and fibrillation, and cardiac arrest. 9

• Patients over 65 years, particularly those with hypertension, may be at increased risk for experiencing hypotensive effects of bupivacaine. 9

Shared Decision-Making Requirement

• Patients must be counseled about potential complications including dural puncture, insertion-site infections, cauda equina syndrome, sensorimotor deficits, discitis, epidural granuloma, and retinal complications before proceeding with caudal epidural injection. 4, 5, 6

Common Pitfalls to Avoid

• Do not perform caudal epidural injections for non-radicular low back pain—the American Academy of Neurology explicitly recommends against epidural steroid injections for non-radicular low back pain due to limited supporting evidence. 4, 6

• Do not repeat injections without documented objective benefit—repeat therapeutic injection requires the initial injection resulted in at least 50% pain relief lasting at least 2 weeks to 2 months depending on the guideline source. 4, 5, 6

• Do not ignore alternative pain generators such as sacroiliac joint pathology when physical examination suggests their involvement. 4, 6

• Do not perform caudal epidural injections without fluoroscopic or ultrasound guidance—image guidance is non-negotiable to ensure proper needle placement and minimize complications. 4, 5, 6, 3

Clinical Algorithm for Decision-Making

Step 1: Confirm Radicular Component

• Verify pain radiates below the knee with dermatomal distribution 4, 5
• Document positive straight leg raise or other radicular signs 2, 7

Step 2: Verify Conservative Treatment Failure

• Confirm at least 4-6 weeks of failed conservative therapy including physical therapy, NSAIDs, and activity modification 4, 5, 6

Step 3: Obtain Appropriate Imaging

• MRI must demonstrate nerve root compression correlating with clinical symptoms 4, 5, 6
• Imaging should be within 24 months prior to injection 4

Step 4: Rule Out Alternative Pain Generators

• Perform sacroiliac joint provocation tests if buttock pain is prominent 4
• Consider facet-mediated pain if response to epidural injections is inadequate 8

Step 5: Perform Image-Guided Caudal Epidural Injection

• Use fluoroscopic or ultrasound guidance 4, 5, 6, 3
• Inject 10 ml volume containing local anesthetic, corticosteroid, and saline 3, 7
• Document needle position and contrast spread pattern 3

Step 6: Assess Response and Plan Follow-Up

• Evaluate pain relief at 15 days, 1 month, 3 months, and 6 months 2, 7
• Consider repeat injection only if ≥50% pain relief lasting ≥2 months 5, 6
• Integrate with ongoing physical therapy and multimodal pain management 4, 5, 6