Epidural steroid injections have been utilized for pain relief since 1952. When indicated, epidural steroid injections are an invaluable non-surgical treatment for low-back pain radiating to the lower extremities and less commonly, neck pain radiating to the arms. The procedure involves the administration of steroids into to the epidural space. If successful, epidural steroid injections will provide pain relief, allowing restoration of function and/or return to a physical therapy regimen.
The spinal cord and brain are covered by three protective layers known as meninges. The innermost layer is the pia mater, which articulates directly with the surface of the spinal cord. The middle layer is known as the arachnoid mater. Lastly, the dura mater is the outermost and thus toughest protective layer of the spinal cord. It is separated from the vertebrae by the epidural space. The epidural space contains the dural sac, blood vessels, fat, connective tissue and spinal nerves. The contents of the dural sac include the spinal cord (ending at L1/L2) and the cauda equina. The spinal dura mater is critical to the peripheral nervous system as it creates pathways (via dural sheaths) by surrounding exiting nerve roots from the spinal cord.
The vertebral column also acts to protect the spinal cord. It consists of 33 bones (vertebrae), many of which are separated by an intervertebral disc. This includes seven cervical, 12 thoracic, five lumbar, five sacral (fused), and four coccygeal (fused) vertebrae. Spinal nerve roots exit the spinal column via two lateral openings, called intervertebral foramina, formed between two contiguous vertebrae.
Epidural steroid injections treat pain caused by irritation and inflammation of spinal nerve roots. One specific type of pain, known as radicular pain, causes radiation along the dermatome of the affected spinal nerve. Many conditions may irritate the spinal nerve roots, which most commonly presents with low back (lumbar) pain with radiation down the buttocks or legs (e.g., sciatica). Also prevalent are patients with neck (cervical) pain with radiation to the arms.
The most common cause of spinal nerve root irritation is intervertebral disc pathology. In herniated discs, the center portion of the disc (nucleus pulposus) pushes through the outer layer (annulus fibrosis) placing pressure and ‘pinching’ the adjacent spinal nerve root. This pressure results in pain, weakness, and/or numbness in the distribution of the irritated nerve. Similarly, in degenerative disc disease, the breakdown of intervertebral discs over time may cause the collapse of intervertebral space resulting in compression of spinal nerve roots.
Another common indication for epidural steroid injection is nerve root irritation secondary to spinal stenosis. Spinal stenosis is a condition causing narrowing (stenosis) of the spinal canal or the canals of exiting nerve roots. Spinal stenosis is most commonly caused by arthritis of the vertebral joints (facets) or intervertebral disc pathology as discussed above.
Other conditions in which epidural steroid injections may be indicated are:
Absolute contraindications to epidural steroid injection include:
Relative contraindications to epidural steroid injections:
Epidural steroid injections require:
Epidural steroid injection may be completed with only topical local anesthesia or under intravenous (IV) sedation. In either case, it is necessary to have blood pressure cuffs, cardiac monitors, and pulse oximeters to monitor vital signs.
Staff includes a physician trained in epidural steroid injections, nurse or assistant, a fluoroscopic C-arm operator, and an anesthesiologist to monitor patient vitals. All staff should be trained for the management of potential complications of the procedure.
Risks and benefits of the procedure should be discussed with the patient and if in agreement, the patient must sign a written consent. Before the injection, a time-out is necessary to verify patient identity and injection site. The patient is to lie in a prone position on the fluoroscopy table, and once the location of injection is identified, the area should be marked, cleaned with betadine, and covered with sterile draping.
Epidural steroid injections may be classified by location (cervical, thoracic, or lumbar) and by the path of the needle (interlaminar, transforaminal, or caudal). In this discussion, we will review the different techniques for interlaminar (between the lamina), transforaminal (across the foramen), and caudal (via the sacrum) epidural steroid injections.
Interlaminar Epidural Steroid Injection (medial approach)
With the patient lying prepped and in a prone position, the interlaminar space between two contiguous vertebrae is identified via an anteroposterior (AP) view on fluoroscopic x-ray. Next, the skin and underlying tissue are injected with local anesthetic (e.g., lidocaine or bupivacaine). Using a midline or paramedian approach between the spinous processes, an epidural spinal needle is inserted into the intended injection site. From superficial to deep, the needle penetrates the skin, subcutaneous tissue, supraspinous ligament (median approach) or paraspinal muscles (paramedian approach), and the ligamentum flavum. A lateral view with the fluoroscopic x-ray is then obtained to confirm the position of the needle. The needle is then advanced using a loss of resistance syringe filled with 1ml of air or normal saline. As the needle passes the ligamentum flavum and enters the posterior epidural space, a sudden loss of resistance will occur allowing the syringe to inject a minimal amount of air or normal saline into epidural space due to the change in pressure. The loss of resistance syringe is then replaced with a syringe filled with the contrast solution, which is then injected to confirm placement of the needle in the epidural space. Once spread of contrast is confirmed in AP and lateral views, steroid (e.g., methylprednisolone, triamcinolone, betamethasone or dexamethasone) with or without local anesthetic is injected into epidural space. Finally, the needle is then withdrawn, and pressure is maintained at the injection site to prevent bleeding.
Transforaminal Epidural Steroid Injection (lateral approach)
With the patient lying prepped and in a prone position, the lateral foraminal space between two contiguous vertebrae is identified via an oblique view on fluoroscopic x-ray. This view displays the classic “Scottie dog,” an anatomical landmark used for needle guidance. Once proper injection site is identified, the skin and underlying tissue are injected with local anesthetic (e.g., lidocaine or bupivacaine). An epidural spinal needle is then inserted and directed under the pedicle of the superior vertebrae. A lateral view on x-ray is obtained to determine needle depth and to prevent damage to the nerve root. The needle is then advanced until it reaches the outer intervertebral foramen. Contrast injection confirms needle position in both lateral and AP views displaying epidural spread. Steroid (e.g., dexamethasone) with or without local anesthetic is then injected into the epidural space. Finally, the needle is withdrawn, and pressure is maintained at the injection site to prevent bleeding.
Caudal Epidural Steroid Injection
With the patient lying prepped and in a prone position, the sacral hiatus is identified via an AP view on fluoroscopic x-ray. Once proper injection site is identified, the skin and underlying tissue are injected with local anesthetic (e.g., lidocaine or bupivacaine). An epidural spinal needle is then inserted and directed through the sacral hiatus. A lateral view on x-ray is obtained to determine needle depth. Needle placement below the S2-3 intervertebral disc space will decrease the risk of dural puncture. Contrast injection confirms needle position in both lateral and AP views displaying epidural spread. The steroid is then injected into the epidural space. Finally, the needle is withdrawn, and pressure is maintained at the injection site to prevent bleeding.
Although rare, possible complications include:
When performed by a skilled physician, epidural steroid injections are a safe and integral treatment of back and leg or neck and arm pain caused by multiple conditions. It is imperative to note that epidural steroid injections are not necessarily designed to cure back or neck pain, instead, they are intended to provide temporary relief so that the patient may return to normal activities and/or continue their physical therapy regimen. Pain relief from epidural steroid injections may vary from one week to one year, and patients may require either a single or a series of injections for maximum relief.