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An epidural needle is a needle used in a nonsurgical procedure to inject an anesthetic and/or medication into the epidural space of the spine. That space is between the vertebrae — the bones of the spinal column — and the dura mater, a thick membrane covering the spinal cord. It is similar to a hypodermic needle in that it has a hallow core; however, while a hypodermic needle has a straight, sharply piercing tip, the epidural needle has a tip that is curved, blunt, and slightly splayed. While each type of needle can be attached to a plastic or glass syringe with volume markings in cubic centimeters (cc), an epidural needle has length markings every 0.40 inch (1 cm) on the needle itself, to clearly show its depth of penetration.
In terms of length, an epidural needle is usually from about 3 inches (7.6 cm) to about 5 inches (12.7 cm). Epidural needle sizes are determined by the diameter of the needle lumen, or inner tube. Gauge sizing is designated in an inverse relationship, with larger gauge numbers indicating smaller needle diameters.
Injections given with epidural needles are called “epidurals,” or “spinal blocks.” They are given most commonly for pain relief during childbirth or for back pain, in general. When given for back pain, a steroid such as cortisone can be added to the anesthetic to help reduce inflammation as well as pain. Pain control is produced when the medication reaches nerve roots in the epidural space and blocks them with dispersed anesthetic.
Placing an epidural injection requires adroit skill and knowledge of spinal anatomy to reach the necessary injection site without harming the spinal cord. For example, each vertebral level has a pair of nerve roots, and each nerve root exits on opposite sides of the spinal column through a bony opening called a foramen. It is necessary for the epidural needle to enter through the foramen next to the nerve root to be anesthetized without accidentally piercing the spinal dura, which can cause severe complications.
Fluoroscopy, a form of X-ray, is commonly used to aid a radiologist or other medical specialist in guiding the epidural needle during an injection. This helps to identify the epidural parts and avoid the serious complications that can result from puncturing the spinal cord membranes. Fluoroscopy can also help identify whether the epidural space is “segmented,” such as by development of fibrous bands associated with aging, which can make epidural injections more difficult without the aid of this visualizing equipment.