A caudal epidural injection approaches the epidural space through the sacral hiatus — a naturally occurring anatomical opening at the base of the sacrum formed by the failure of fusion of the S4 and S5 laminae. This approach provides access to the epidural space at a level below the termination of the spinal cord (which typically ends at L1-L2 in adults), thereby carrying a significantly lower risk of dural puncture and spinal cord injury compared to lumbar or thoracic approaches.
The caudal route is particularly advantageous for patients with prior lumbar spine surgery where scar tissue or hardware may impede access to the epidural space via the interlaminar or transforaminal routes. Additionally, the caudal approach accommodates larger injectate volumes, enabling medication spread to reach multiple lumbosacral nerve roots simultaneously.
The physician identifies the sacral hiatus by palpation of anatomical landmarks (the sacral cornua) and confirms the location with fluoroscopic imaging in the lateral projection. A needle is advanced through the sacrococcygeal ligament into the caudal epidural space. Contrast medium injection under live fluoroscopy confirms appropriate epidural spread pattern, which should appear as a "Christmas tree" or "sleeve-like" pattern along the lumbosacral nerve roots. Once accurate placement is confirmed, a therapeutic volume of corticosteroid and local anesthetic is delivered.
The larger volume capacity of the caudal approach (typically 6-15 mL) allows the medication to spread cephalad, reaching nerve roots as high as L2-L3 depending on the volume administered and the patient's individual anatomy.
The patient lies prone for this 15-20 minute outpatient procedure. The injection site is near the top of the gluteal cleft at the level of the sacral hiatus. The procedure is well-tolerated under local anesthesia alone, though light sedation may be offered for patient comfort. This is frequently the preferred approach for patients with prior lumbar surgery, as it avoids the scarred surgical field.
Mild soreness near the tailbone is common for 1-2 days. Patients may resume normal activities within 24-48 hours. As with other epidural injections, the therapeutic benefit of the corticosteroid begins within 3-7 days and continues to improve over the subsequent 2 weeks.
The caudal approach is historically the oldest technique for accessing the epidural space and remains an essential tool in the interventional pain physician's armamentarium. While straightforward in concept, successful caudal epidural injection requires accurate identification of the sacral hiatus, which can be challenging in patients with obesity, sacral anatomical variants, or prior sacral trauma. Ultrasound guidance may be used adjunctively to identify the hiatus in difficult cases. At IPC, our physicians have extensive experience with the caudal approach and routinely employ it for appropriately selected patients.
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