An epidural is placed in your lower back, typically between the second and fourth lumbar vertebrae. The needle enters a narrow space just outside the membrane that surrounds your spinal cord, called the epidural space. For most people, that space sits about 4 to 5 centimeters beneath the skin surface, though it can be deeper depending on body size.
The Exact Spot on Your Back
Your spine is made up of stacked bones (vertebrae) with small gaps between them. The anesthesiologist targets one of these gaps in your lower back, most commonly between the L3 and L4 vertebrae or between L2 and L3. If you put your hands on your hips, your thumbs roughly line up with the L4 vertebra, so the insertion point is right around that level or slightly above it.
The needle doesn’t go into bone or into your spinal cord. It passes between two vertebrae and stops in a cushioned space that contains fat, connective tissue, and the nerve roots branching off your spinal cord. The medication bathes those nerve roots and blocks pain signals from traveling up to your brain.
What the Needle Passes Through
From the skin inward, the needle travels through several layers: skin, a layer of subcutaneous fat, then two ligaments that connect your vertebrae together (the supraspinous and interspinous ligaments), and finally a thick, rubbery ligament called the ligamentum flavum. This last ligament is the gateway. Once the needle tip pushes through it, it enters the epidural space.
The epidural space sits between that ligament on the outside and the dura mater on the inside. The dura is a tough protective membrane wrapped around your spinal cord and the fluid it floats in. The goal is to get the needle past the ligament but stop before piercing the dura. That’s a small but well-defined target, and anesthesiologists use a specific technique to find it precisely.
How the Provider Finds the Right Spot
The standard method is called “loss of resistance.” As the needle advances through the dense ligaments, the provider gently presses on a syringe filled with saline or air attached to the needle. The ligaments resist that pressure. The moment the needle tip crosses into the epidural space, the resistance suddenly drops and the syringe plunges easily. That sudden change tells the provider the needle is exactly where it needs to be.
Once the needle is positioned, a thin, flexible catheter (a soft plastic tube) is threaded through the needle into the epidural space. The needle is then removed, leaving only the catheter behind. This catheter is taped securely to your back so medication can be delivered continuously or in repeated doses without another needle stick.
How Deep the Needle Goes
In adults with a BMI under 30, the average distance from skin to the epidural space is about 4.2 centimeters (roughly 1.6 inches). In people with a BMI over 30, the average depth increases to about 5.2 centimeters. At higher body weights, it can reach 6 centimeters or more. The depth doesn’t change meaningfully with age or sex, but it does track closely with weight and body composition.
How You’ll Be Positioned
You’ll either sit up on the edge of the bed or lie on your side in a curled position. The sitting position is more common. Your feet go on a stool, your knees bend, and you’re asked to round your back forward as much as you can, like you’re hugging a big beach ball. This curving posture opens up the gaps between your vertebrae, giving the needle a wider target and bringing the epidural space closer to the surface.
If you’re lying on your side, you’ll curl into a similar rounded shape with your knees drawn toward your chest. Either way, staying still during the insertion is the most important thing you can do to help.
What It Feels Like
Before the epidural needle goes in, the provider numbs the skin with a small injection of local anesthetic. That feels like a brief pinch or sting, similar to any other shot. Once the area is numb, you may feel pressure as the epidural needle advances, and some people notice tingling, a brief burning sensation, or a momentary jolt. Others feel nothing beyond the initial numbing injection. Any discomfort typically stops as soon as the needle is in position.
How It Differs From a Spinal Block
People often confuse epidurals with spinal blocks because both go into your lower back. The difference is depth. An epidural stops in the epidural space, outside the dura membrane. A spinal block goes one layer deeper, through the dura and into the fluid surrounding the spinal cord (the subarachnoid space). Because a spinal delivers medication directly into that fluid, it works faster and produces more complete numbness but wears off sooner. An epidural, with its catheter left in place, can deliver medication for hours or even days.
One rare complication of epidural placement is accidentally puncturing the dura, which happens in less than 1% of cases. When it does occur, it can cause a distinctive headache in the days afterward, though this affects only about 0.4% of patients receiving labor epidurals.
When Placement Gets More Complicated
Certain spinal conditions can make finding the epidural space harder. Severe scoliosis, for instance, rotates and tilts the vertebrae so the usual landmarks don’t line up. In those cases, providers may use imaging like CT scans beforehand to map out the best entry point. For people with significant spinal curvature (a Cobb’s angle greater than 50 degrees), the provider may enter from the convex side of the curve, where the epidural space is wider, sometimes measuring 3 to 5 centimeters across. Previous spinal surgery with hardware in the lower back can also limit where the needle can safely go, and the provider will choose a level above or below the surgical site.
For most people, though, epidural placement is straightforward. The lower lumbar spine is the standard target, the procedure takes just a few minutes, and the catheter stays comfortably taped in place for as long as pain relief is needed.