A bilateral injection is any injection performed on both sides of the body during the same procedure. The term “bilateral” simply means “both sides,” so instead of treating just the left or right side, the provider delivers the injection to both. This applies across many areas of medicine, from spinal pain management to cosmetic treatments.
What “Bilateral” Means in Medical Terms
Your body has many structures that are symmetrical or come in pairs. The spine, for instance, is a single structure with a left side and a right side that mirror each other. Joints like the sacroiliac joints, knees, and shoulders exist as pairs. When a provider performs a bilateral injection, they’re treating both sides of one of these symmetrical structures or treating both members of a paired structure.
The opposite is a unilateral injection, which targets only one side. Whether you need a unilateral or bilateral injection depends entirely on where your symptoms are. Someone with pain radiating down both legs, for example, would be a candidate for bilateral injections, while someone with pain only on the left side would typically receive a unilateral injection.
Where Bilateral Injections Are Most Common
Bilateral injections show up in several areas of medicine, but spinal pain management is where you’ll encounter the term most often.
Facet Joint Injections
The facet joints are small joints along the back of your spine that allow it to bend and twist. They’re a source of pain in 15% to 45% of people with low back pain, 54% to 67% of people with neck pain, and about 48% of people with mid-back (thoracic) pain. When these joints become inflamed or arthritic on both sides of the spine, bilateral facet joint injections deliver a numbing agent and a steroid to both sides at the same level. These injections serve two purposes: confirming that the facet joints are actually the source of pain (diagnostic) and reducing inflammation to provide relief (therapeutic).
Providers typically recommend facet injections when chronic back or neck pain hasn’t responded to anti-inflammatory medications and physical therapy, or after spinal surgery when pain persists without a clear cause like a recurring disc problem.
Epidural Steroid Injections
Transforaminal epidural steroid injections target nerve roots in the spine to treat pain caused by disc herniations or spinal stenosis. Most published research has focused on unilateral injections, but unilateral epidurals don’t effectively spread medication across the midline of the spine. For people experiencing pain on both sides, bilateral transforaminal injections allow the steroid to distribute to both sides, which can produce greater improvement in bilateral symptoms.
These bilateral epidurals have become a viable option particularly for patients who’ve had prior spinal fusions or laminectomies and developed pain on both sides afterward.
Sacroiliac Joint Injections
The sacroiliac (SI) joints sit where the base of your spine meets the pelvis, one on each side. When both joints are involved, bilateral SI joint injections treat each side during the same visit. This is common in older adults with degenerative changes. In some cases, bone spurs or joint narrowing can make the standard approach difficult, requiring the provider to use an alternative needle angle to access the joint.
Cosmetic and Therapeutic Botulinum Toxin
Bilateral injections are standard in cosmetic and therapeutic uses of botulinum toxin. Masseter injections for jaw slimming or teeth grinding, for example, are almost always bilateral because both jaw muscles need to be treated for a balanced result. Providers typically use multiple injection points per side, distributing small doses (often around 30 units per muscle) across the width of each muscle for even effect. The exact number of units on each side may differ slightly if one muscle is larger than the other.
What the Procedure Feels Like
A bilateral injection takes somewhat longer than a unilateral one because the provider repeats the process on the second side. For spinal injections, you’ll lie face down while imaging guidance (usually fluoroscopy, a type of live X-ray) helps the provider position the needle precisely. The skin is numbed with a local anesthetic before the deeper injection, so most people feel pressure rather than sharp pain.
After the procedure, you’re typically monitored for 15 to 20 minutes before going home. You may feel soreness at the injection sites for several hours. Pain can actually increase for two to three days before improving, which is normal. The steroid component generally takes three to five days to start working. Most people are told to take it easy for the rest of the day but can return to normal activities shortly after.
Dosage Considerations
One important factor in bilateral injections is the total amount of medication used. Because both sides are being treated, the combined dose is higher than for a single-sided injection. Local anesthetics have maximum safe doses based on body weight. Exceeding those limits can cause systemic reactions ranging from numbness around the mouth and ringing in the ears to more serious complications. Providers calculate the total volume needed for both sides before the procedure to stay within safe limits.
This is one reason bilateral injections require careful planning. It’s not simply a matter of doubling what would be given on one side. The provider accounts for the cumulative dose across both injection sites.
How Bilateral Injections Are Billed
If you’re looking at a medical bill or an explanation of benefits, bilateral injections are coded differently than two separate unilateral injections. The standard practice is to use a “modifier 50,” which tells the insurance company that a single procedure was performed on both sides during the same session. This is submitted as one line item on the claim rather than two.
The payment adjustment for bilateral procedures is typically 150% of the unilateral rate, not 200%. So insurance pays one and a half times the single-side amount, reflecting that the second side takes less additional time and resources than performing two completely separate procedures. If a bilateral procedure is incorrectly billed as two unilateral procedures (using left and right modifiers separately), it can result in claim processing errors or denials.