A caudal epidural steroid injection is used to treat acute or chronic lower back pain and sciatica, typically characterized by central or bilateral back pain. These symptoms often result from heavy lifting, prolonged sitting, or gradually developing discomfort.
This type of pain presents as central or bilateral pain in the lower back, which may or may not be accompanied by sciatica or nerve root signs and symptoms. Patients often experience painful bending, usually leaning away from the side of the pain.
In most people, the spinal cord ends at the L1 level, while the thecal sac terminates at S2. The goal of this injection is to deliver an anti-inflammatory solution into the spinal canal through the sacral hiatus. This allows the medication to reach the back of the disc, the front of the dura mater, and any affected nerve roots in the central region.
Two palpable prominences, known as the sacral cornua, are located at the apex of an equilateral triangle formed between the posterior superior iliac spines and the coccyx. The canal entrance is protected by a thick ligament, and needle placement must account for the varying angle of the canal’s curvature.
Advise the patient to maintain an active lifestyle while respecting their pain limits and suggest reassessing the situation in about ten days. If the initial caudal steroid injection provides only partial relief, it can be repeated as long as improvement continues.
It is also important to address the underlying causes of back pain, such as weight management, posture, workplace ergonomics, proper lifting techniques, exercise programs, and strengthening the abdominal muscles.
Due to the limitations of the blind technique, some experts recommend performing caudal epidural injections under fluoroscopic guidance.
For a fluoroscopy-guided caudal epidural block, the patient is typically placed in a prone position. A lateral fluoroscopic view helps identify the sacral hiatus, which appears as a sudden drop at the end of the S4 lamina. This allows for visualization and navigation of the needle path into the sacral canal. Injecting contrast dye under fluoroscopy confirms correct placement of the needle tip in the sacral epidural space and helps detect any intravascular or intrathecal placement.
Fluoroscopic guidance has significantly improved the success rate of caudal epidural blocks and is now considered the standard method. However, its routine use is limited by factors such as radiation exposure, cost, and the need for specialized space.
The ultrasound-guided caudal injection technique was first introduced by Klocke and colleagues in 2003. It has since become very popular, with consistently high success rates ranging from 96.9% to 100% in several studies across different ethnic populations.
To perform an ultrasound-guided caudal injection, the patient can be positioned either prone or on their side. A linear transducer with a frequency of 7–13 MHz is typically suitable for most caudal epidural injections. However, a curved transducer with a frequency of 2–5 MHz may be necessary for obese patients.
First, the ultrasound transducer is placed transversely over the midline to obtain a transverse view of the sacral hiatus. In this view, the two sacral cornua appear as echogenic structures. Between these horns, two band-like echogenic structures are visible. The superficial one corresponds to the sacrococcygeal ligament (SCL), while the deeper one represents the dorsal surface of the sacrum. The sacral hiatus, the target area, appears as a hypoechoic region between these two band-like structures.
Once the transverse view is obtained, the ultrasound transducer is rotated 90 degrees to get a longitudinal view of the sacral hiatus. In this view, the block needle is inserted using the “in-plane” technique. Real-time ultrasound imaging allows visualization of the needle as it punctures the SCL and enters the sacral hiatus.
However, the needle cannot be seen beyond the apex of the sacral hiatus. To prevent a dural puncture, it is recommended to limit the advancement of the needle tip beyond the apex of the sacral hiatus to a maximum of 5 mm. This precaution is necessary because the distance between the tip of the sacral hiatus and the end of the dural sac can be less than 6 mm in some cases.
If clear fluid or blood is aspirated during the procedure, the injection should be abandoned. A reattempt can be made after a few days. Sometimes, accessing the canal can be difficult due to a split or very narrow canal, or because the sacrum is strongly curved. In such cases, injecting a small amount of local anesthetic into the ligament can improve comfort when repositioning the needle.
If the affected level is above the typical L5-S1 level or if the patient is larger, a larger volume may be needed. In these situations, we recommend using 40 mg of Adcortyl or adding up to 9 ml of normal saline to the Kenalog.
In a randomized controlled trial, caudal epidural steroid injections appear to be effective for treating patients with lower back pain and sciatica. They are simple to perform, technically less demanding, and have a low complication rate compared to conservative treatment. Caudal epidural injections can offer an interesting alternative approach for managing lower back pain and sciatica.
