Epidural Space Anatomy and Injections

The epidural space is an area of spinal anatomy that is located between the vertebral canal and the spinal cord. It lies inside the canal, but outside the cord.

Epidural Space Anatomy

Three layers of tissue cover the spinal cord, and between each is a "space." The epidural space is the area between the outermost layer of tissue and the inside surface of bone in which the spinal cord is contained, i.e., the inside surface of the spinal canal. The epidural space runs the length of the spine.

The other two "spaces" are in the spinal cord itself. They are the sub-dural and sub-arachnoid spaces, named after some, but not all, of the other tissue coverings that surround the spinal cord. 

The epidural space contains fat, veins, arteries, spinal nerve roots and lymphatics.

The fat in the epidural space helps absorb shock, which protects the other contents in the area, as well as the dura. The dura is the outermost layer of the covering, called the meninges, that surrounds the spinal cord. Most drugs are injected outside of the dura, into the epidural space.

The arteries supply the bones and ligaments in the space, as well as the cervical part of the spinal cord, with blood. They tend to be located at the sides of the epidural space. Should they be traumatized, a hematoma, which is swelling that clots into a mass, may form and/or the blood supply to the spinal cord may become disrupted or otherwise compromised.

Arteries enter through the many passageways that are present in the epidural space.

The epidural veins are mainly located to the front part of the side of the space. The veins play roles in volume changes that occur in the space, which in turn may affect drug delivery as well as the spread of blood related infection through the spinal column.

Lymphatics in the epidural space tend to be located near the dura; their job is to remove foreign material from both the epidural and subarachnoid spaces.

Epidural Injections for Neck or Back Related Pain

If you’ve ever had an injection to help reduce inflammation and/or relieve nerve symptoms that go down one arm or leg, your healthcare provider may have inserted a needle into your epidural space. In this treatment, the needle is inserted right over a compressed spinal nerve root, which, in most cases is where the pain starts, to distribute medication. The medication may be a local anesthetic, a steroid drug, or a combination of the two.

While it's true that epidural injections involve the puncturing of your skin and access to your internal structures, healthcare providers consider this treatment a minimally invasive one. This is likely because it is not a surgery. Some experts refer to these minimally invasive procedures as “conservative” therapy.

Intralaminar Epidural Injections

Epidural injections are among the most common back treatments. And the most common type of epidural injection given for neck or back pain is the intralaminar injection. 

In an interlaminar injection, the needle is aimed upwards toward your head and in between two adjacent lamina. The lamina is a part of the bony ring located in back of the vertebral body. 

How well do interlaminar epidural injections work?

A 2012 July-August issue of the journal Pain Physician evaluated 26 medical studies to see  how effective interlaminar epidural injections were for relieving symptoms associated with common spine problems.

The researchers found good evidence that epidural injections may help relieve pain from a compressed nerve root (radiculitis) brought about by a disc herniation — as long as the medication used was local anesthtics and steroids. But this was about symptom abatement only: evidence that an epidural injection could help heal up the disc herniation was not identified.

The researchers also found fair quality evidence that epidurals with local anesthetics or steroids may help symptoms of a compressed nerve root that are related to spinal stenosis.  

A 2018 study published in the January issue of World Neurosurgery found that epidural steroid injections into the neck area seem to be viable for managing chronic neck pain that presents itself at the back of the cervical spine, and that is brought on by central spinal stenosis. The authors found epidural steroids particularly useful when pain medications taken by mouth prove ineffective at relieving symptoms.