Pain near the belt line or upper buttock is often blamed on the lower back. Sometimes the painful structure is the sacroiliac joint, usually shortened to the SI joint. This joint connects the triangular sacrum at the base of the spine to the two sides of the pelvis. It transfers load between the trunk and legs while allowing only a small amount of motion.
The difficult part is that SI joint pain can resemble a lumbar disc problem, hip arthritis, a tendon problem, or several other conditions. An MRI finding by itself usually cannot prove where the pain begins. A careful evaluation combines the pain pattern, examination, appropriate imaging, and sometimes a precisely placed diagnostic injection.
Most people with suspected SI joint pain do not begin with surgery. Treatment usually starts with activity modification, medication when appropriate, and a focused rehabilitation program. Fusion is reserved for selected patients whose pain has been convincingly traced to the SI joint and remains disabling despite a substantial nonsurgical plan.
What SI joint pain can feel like
SI joint pain is commonly felt on one side near the small hollow just below the belt line. It may spread into the buttock, outer hip, groin, or upper thigh. Pain below the knee is less typical and raises concern for a nerve problem, although symptoms do not always follow a textbook pattern.
Activities that load the pelvis unevenly may aggravate symptoms. Examples include:
- standing on one leg to put on pants
- climbing stairs
- getting in or out of a car
- rolling over in bed
- rising from a low chair
- taking long strides, running, or carrying a child on one hip
- standing or sitting for a long time
Some patients remember a fall, pregnancy-related pelvic symptoms, or another injury. Others develop pain gradually. Prior lumbar fusion can also change how forces pass through the pelvis, but it does not mean every new ache is coming from the SI joint.
Why diagnosis requires more than an MRI
X-rays, CT, and MRI can identify arthritis, fracture, infection, inflammatory disease, tumor, or another structural problem. They also help evaluate the nearby hips and lumbar spine. However, ordinary age-related changes on imaging may be painless, and painful SI joint dysfunction may not produce a dramatic scan.
The examination therefore matters. A clinician may use several maneuvers that place controlled stress across the SI joint. No single maneuver is definitive. A consistent pain pattern reproduced by a cluster of tests is more meaningful than one positive test in isolation. The 2024 American Society of Pain and Neuroscience best-practice guideline describes history, multiple provocative maneuvers, imaging to exclude competing diagnoses, and image-guided diagnostic injection as complementary parts of the assessment.1
An image-guided diagnostic injection places local anesthetic inside the SI joint. Substantial temporary relief supports the joint as an important pain source. The response must still be interpreted in context because anesthetic can spread, pain varies from day to day, and more than one structure may hurt.
Problems that can mimic SI joint pain
Several conditions can produce pain in the same region:
- lumbar nerve compression, which may cause electric pain, tingling, numbness, or weakness
- lumbar facet or disc-related pain
- hip arthritis, often associated with groin pain and reduced hip rotation
- gluteal tendon pain, usually tender along the outer hip
- hamstring or other tendon injury
- sacral stress or insufficiency fracture
- inflammatory sacroiliitis
- infection, tumor, or abdominal and pelvic disorders
This overlap is why an examination should not jump directly from “buttock pain” to an injection or fusion. The goal is to identify the dominant pain generator and make sure a dangerous or more treatable alternative is not being missed.
When symptoms need urgent attention
Seek urgent medical evaluation for new loss of bowel or bladder control, numbness around the groin or saddle area, rapidly progressive leg weakness, fever with severe back or pelvic pain, or pain after major trauma. Sudden inability to bear weight, unexplained weight loss, a history of cancer, or severe night pain also deserves prompt assessment.
These findings are not typical uncomplicated SI joint pain. They may signal nerve compression, fracture, infection, tumor, or another condition that should not wait for a routine office visit.
Nonsurgical treatment comes first
Initial care depends on the diagnosis and medical history. It may include temporarily reducing the activities that repeatedly flare the joint without stopping all movement. A short course of an anti-inflammatory medication may be reasonable for some patients, but kidney disease, ulcers, blood thinners, heart disease, allergies, and other conditions can make these medicines unsafe. Acetaminophen may be an alternative for some people but also requires attention to liver disease and total daily dose.
Physical therapy is usually more useful when it is specific rather than generic. The program may address:
- trunk and hip strength
- control of pelvic rotation during walking, stairs, and single-leg tasks
- hip mobility when stiffness is shifting stress toward the pelvis
- graded return to work, exercise, lifting, or running
- practical changes to sleep position and daily movement
The purpose is not to “put the pelvis back in place.” It is to improve how the surrounding muscles share load and to restore tolerance for the activities that matter. Pacific Bone & Joint offers integrated physical therapy and orthopedic rehabilitation when a coordinated plan is appropriate.
An SI belt may help selected patients, particularly when external compression clearly improves function, but it is not a substitute for diagnosis and progressive rehabilitation.
What injections can and cannot do
An image-guided SI joint injection may serve two purposes. Local anesthetic can provide diagnostic information, and corticosteroid may reduce inflammation for a period of time. The duration of relief varies. A helpful response does not guarantee that repeated injections will remain effective, and an unsuccessful injection should prompt a review of needle placement, diagnosis, and competing pain sources.
Radiofrequency procedures target nerves that carry pain signals from the region. They may help selected patients, but techniques and coverage vary, and nerve treatment does not fuse or mechanically stabilize the joint. A discussion should include the expected duration, alternatives, risks, and what happens if symptoms return.
When minimally invasive SI joint fusion enters the discussion
Fusion is not a first-line treatment for nonspecific low-back pain. It may be considered when all of the following point in the same direction:
- pain has remained substantial and function-limiting despite an adequate nonsurgical program
- the history and examination repeatedly localize symptoms to the SI joint
- hip, spine, fracture, inflammatory, and other causes have been evaluated
- one or more image-guided diagnostic blocks produce convincing temporary relief
- the patient understands the rehabilitation, restrictions, risks, alternatives, and uncertainty
Minimally invasive techniques place implants across the joint through small incisions to reduce painful motion and promote fusion. The exact approach and implant depend on anatomy, diagnosis, surgeon training, and the evidence supporting that system. You can read more about Pacific Bone & Joint’s SI joint fusion evaluation and treatment approach.
A randomized trial found greater improvement with one lateral minimally invasive fusion system than with nonsurgical management in carefully selected participants at two years.2 A later systematic review found overall improvement across published studies but also emphasized variation in study quality, devices, and techniques.3 A 2026 evidence review similarly concluded that more high-quality long-term and direct comparative research is needed.4
Those findings matter because results from one implant or approach should not automatically be applied to every technique. Evidence should support both the decision to fuse and the specific method being proposed.
Risks and alternatives
Potential risks include infection, bleeding, blood clot, nerve injury, persistent or recurrent pain, implant malposition, failure of the bones to fuse, fracture, and the need for another procedure. Some patients improve only partially even when the operation and imaging appear satisfactory.
Alternatives may include continued activity modification, a revised therapy program, medication, an SI belt, targeted injection, selected radiofrequency treatment, or evaluation of another pain source. Choosing continued nonsurgical care is reasonable when the diagnosis remains uncertain or symptoms are manageable.
Questions to bring to an SI joint evaluation
Useful questions include:
- Which findings make the SI joint more likely than my hip or lumbar spine?
- Do I need X-rays, CT, MRI, or a diagnostic injection?
- What should my rehabilitation program target?
- If an injection helps only briefly, what does that mean?
- What evidence supports the proposed fusion approach and implant?
- What restrictions, recovery milestones, and complications should I expect?
- Which findings would make you reconsider the diagnosis?
The most reliable treatment plan begins with diagnostic discipline. If pain has been repeatedly labeled “low back pain” without a clear explanation, a structured hip, spine, and SI joint evaluation can help identify the next useful step.
Request an SI joint evaluation in Hawaii to review the diagnosis, nonsurgical options, and whether fusion deserves consideration.
Sources and further reading
- American Society of Pain and Neuroscience best-practice guideline for sacroiliac disorders
- Two-year randomized trial of minimally invasive SI joint fusion versus nonsurgical management
- Systematic review of minimally invasive SI joint fusion effectiveness and safety
- 2026 review of SI joint fusion techniques and evidence gaps
- CMS coverage guidance for minimally invasive SI joint arthrodesis
