The pain sits low and off to one side, right about where a back pocket rests. Standing up after a long drive on the New Jersey Turnpike sets it off. Rolling over in bed can hurt, too.
An MRI might show a bulging disc that doesn’t explain the symptoms, or nothing unusual at all. The problem could be coming from the spine, the hip, or the joint where the spine meets the pelvis. An SI joint injection can help a pain specialist narrow that search by testing whether numbing the joint changes the pain.
Quick Answer
An SI joint injection can help identify whether the sacroiliac joint is contributing to low back pain. A doctor uses imaging to place numbing medicine in the joint, then evaluates how much the patient’s usual pain improves. Significant relief during the anesthetic’s short window supports an SI joint source. If a steroid is also used, longer-lasting relief may follow.
Why SI Joint Pain Is Hard to Pin Down
The two sacroiliac joints sit where the base of the spine meets the pelvis. They move very little, but they help transfer weight between the upper body and legs. A clinical review in StatPearls estimates that SI joint problems account for roughly 10% to 27% of mechanical low back pain.
SI pain commonly sits below the belt line, often more on one side, and may spread into the buttock, groin, or back of the thigh. Climbing stairs can aggravate it. So can standing on one leg to pull on a pair of pants.
Inflammation involving the joint is called sacroiliitis. It can come with inflammatory arthritis such as ankylosing spondylitis, where stiffness is often worst in the morning and eases with movement.
Other SI problems are mechanical. Pregnancy changes how the pelvis carries weight and can loosen the ligaments that steady the joint. Degenerative arthritis, a fall, a car accident, or an earlier lumbar fusion may also contribute. After a fusion, the SI joints sometimes absorb more mechanical stress because the fused portion of the spine no longer moves normally.
During an examination, the doctor may press on or move the pelvis in several directions to reproduce the familiar ache. The American Society of Pain and Neuroscience (ASPN) identifies three positive findings among five common provocation tests as useful evidence for SI joint dysfunction. Even so, a problem in the hip or lumbar spine can produce similar symptoms, and nearby muscle trigger points may cause a deep ache in roughly the same region.
What an SI Joint Injection Reveals in the First Few Hours
A diagnostic injection asks a specific question: if the SI joint is contributing to the pain, what happens when the doctor temporarily numbs it?
During an image-guided SI joint injection, local anesthetic is placed inside the joint. Depending on the medication, the numbing effect usually lasts only a few hours.
The important result isn’t simply feeling comfortable while lying still. Plenty of back problems hurt less when there’s no weight on the painful area.
Suppose getting out of a chair usually causes sharp pain. Before the injection, the patient rates it 8 out of 10. During the numbing window, the same movement produces pain rated 2 out of 10. That’s a 75% reduction.
The cutoff isn’t identical in every diagnostic protocol. Some use 75% or greater pain relief, while the ASPN’s 2024 guideline accepts more than 50% relief after an appropriately performed anesthetic-only SI joint injection. Numbing medicine can also spread to nearby structures, and a person may have more than one source of low back pain.
Why the Doctor Uses Live X-Ray Guidance
The SI joint lies deep in the pelvis and has a narrow, irregular joint space. Reaching it accurately by feel alone is difficult.
StatPearls reports that unguided injections place the needle inside the joint in only about 12% to 22% of cases. That’s a serious limitation when the purpose is to find out whether the joint itself is painful.
With fluoroscopy, a type of live X-ray, the doctor can see the needle’s position. Contrast dye is commonly used to confirm that the medication will enter the intended joint space. If an injection misses the joint, a lack of relief may say more about needle placement than the patient’s diagnosis.
Diagnostic and therapeutic injections also have different goals. An anesthetic-only block is intended to test the source of pain. A therapeutic injection may include a corticosteroid to reduce inflammation and provide longer relief. Some treatment sessions combine anesthetic and steroid, although adding steroid can make a strictly diagnostic result less specific.
Planning an SI Joint Injection in Elizabeth, NJ
The procedure is generally performed without an overnight hospital stay. Patients typically lie face down while the clinician cleans the skin, numbs the injection area, and guides a needle into the intended location.
When back pain follows a car accident or a lifting injury at work, the appointment may involve more than the procedure itself. Prior imaging, medication history, and auto-insurance or workers’ compensation paperwork may all need reviewing. A practice offering pain management Elizabeth NJ residents use after those injuries can help confirm insurance authorization before the injection is scheduled.
An outpatient procedure isn’t necessarily something to squeeze into a lunch break. The clinical team will monitor the patient afterward and check that it’s safe to leave, and sedation can add further restrictions. Arrange for someone to drive home, and don’t plan on heading straight from the appointment to another shift.
What Recovery Feels Like After the Injection
The needle site may feel sore for a day or two. Some patients also notice a temporary increase in their familiar pain when the anesthetic wears off, before any steroid benefit begins.
Temporary leg heaviness or numbness is possible. It should improve as the medication wears off, but patients should follow their clinician’s instructions and report symptoms that persist or worsen.
A steroid, when included, may begin easing inflammation after several days, with fuller benefit sometimes taking a week or two.
People with diabetes should know that corticosteroids can temporarily raise blood sugar. Monitoring may need to be more frequent for several days, according to the treating clinician’s advice.
Fever, increasing redness or drainage at the injection site, or worsening weakness needs prompt medical attention. New problems controlling the bladder or bowels, or new numbness around the groin, warrant emergency evaluation.
What to Ask Before the Injection
A few questions help patients understand what their appointment is meant to accomplish:
- Is this a diagnostic block, a steroid treatment, or both? The purpose affects when pain relief should be measured.
- Will the injection use imaging guidance? Accurate placement is important for interpreting a diagnostic result.
- Will I need a driver or time away from work? Ask about sedation, temporary numbness, and the clinic’s activity restrictions.
- Which movements should I use to assess relief? The clinician can identify safe activities that normally reproduce the pain.
How Long Does an SI Joint Injection Last?
The numbing medicine usually lasts a few hours. For the steroid, multisociety recommendations published in Regional Anesthesia & Pain Medicine in 2026 estimate about one to three months of meaningful relief in roughly half of appropriately selected patients. Some people get longer relief, and others get little benefit. Pain relief may also make it easier to participate in physical therapy aimed at improving movement and strength.
How Painful Is the Shot Itself?
Patients commonly feel a sting or brief burning sensation when the skin is numbed, followed by pressure or discomfort as the needle and medication are placed.
Some clinics offer sedation or other medication for patients who need help tolerating the procedure, but sedation isn’t appropriate for every diagnostic block because it can complicate assessment of the pain response. Ask about comfort options when scheduling rather than waiting until the day of treatment.
What If the Injection Doesn’t Help?
A negative response is still useful information, but it doesn’t automatically rule out every SI joint problem.
If the familiar pain barely changes during the expected anesthetic window, the clinician may reconsider whether the hip, lumbar discs, small spinal joints, or surrounding tissues are responsible.
When SI joint pain still seems likely but relief doesn’t last, radiofrequency ablation may be considered. It uses heat to interrupt pain signals carried by certain nerves around the joint. That procedure generally requires its own diagnostic evaluation rather than being selected solely because an SI joint injection helped briefly.
Minimally invasive SI joint fusion, which stabilizes the joint with small implants, is usually considered only after about six months of pain that hasn’t improved with physical therapy and injections, and after diagnostic blocks have pointed strongly to the joint.
Bring a Pain Score From the Morning
Before leaving home, write down the activities that reliably bring on the pain. Getting out of a chair, climbing a few stairs, or turning over in bed may be more informative than how the back feels while resting.
Record a pain score from 0 to 10 for one or two of those activities. If the care team says it’s safe, repeat the same movements during the anesthetic window and write down the new scores. Don’t deliberately strain yourself or test weight-bearing movements if a leg feels numb or weak.
Include the time of each score and when the pain begins returning. Bring the notes to the follow-up appointment.
A patient who can say, “Getting out of the car was an eight before the injection and a two afterward,” gives the specialist something more useful than simply reporting that the shot worked.
