SI joint: Definition, Uses, and Clinical Overview

SI joint Introduction (What it is)

The SI joint is the sacroiliac joint, where the sacrum meets the ilium on each side of the pelvis.
It helps transfer forces between the spine and the legs during standing, walking, and lifting.
In clinical care, the term SI joint is commonly used when discussing certain patterns of low back, buttock, or pelvic pain.

Why SI joint used (Purpose / benefits)

The SI joint matters in orthopedics and rehabilitation for two main reasons: function and pain source identification.

From a functional standpoint, the SI joint is part of the pelvic ring. It contributes to load transfer—moving forces from the upper body (spine) into the lower extremities—while relying on strong ligaments for stability. Even though the SI joint typically moves only a small amount, that small motion can be relevant in activities such as gait, transitions (sitting to standing), and asymmetric tasks (stairs, single-leg stance).

From a clinical standpoint, SI joint is used as a diagnostic label and an anatomic target. Symptoms from the SI joint can overlap with the lumbar spine, hip joint, and surrounding soft tissues, so clinicians may assess the SI joint to clarify where pain is coming from. When SI joint–related pain is suspected, the joint can also be a target for interventions such as image-guided diagnostic injections, therapeutic injections, and in selected cases, SI joint fusion procedures. The overall aim is to improve function and reduce pain when the SI joint is contributing to symptoms.

Indications (When orthopedic clinicians use it)

Clinicians commonly consider the SI joint in situations such as:

• Buttock or low back pain patterns that do not clearly match a single lumbar spine or hip diagnosis
• Pain that may worsen with prolonged standing, walking, or transitional movements (varies by case)
• Evaluation after trauma affecting the pelvis (for example, suspected pelvic ring injury)
• Postpartum or pregnancy-associated pelvic girdle pain assessment (varies by clinician and case)
• Workup of persistent pain after lumbar spine surgery when symptoms suggest an alternative pain generator (varies by clinician and case)
• Suspected inflammatory conditions that can involve the sacroiliac region (evaluation depends on history, exam, and imaging)
• Planning for or monitoring response to image-guided SI joint injections or other interventional pain procedures

Contraindications / when it’s NOT ideal

Focusing on the SI joint—or performing SI joint–targeted procedures—may be less suitable when:

• Symptoms or exam findings strongly suggest another primary source, such as hip osteoarthritis, lumbar radiculopathy, or fracture
• “Red flag” features raise concern for serious conditions (examples include infection or malignancy), requiring a broader diagnostic approach
• There is suspected or confirmed pelvic instability where different urgent management may be needed (varies by clinician and case)
• For injections: local or systemic infection, certain bleeding risks, or medication interactions that affect clotting (screening varies by clinician and setting)
• For steroid-containing injections: clinician concern about short-term side effects in specific medical conditions (varies by clinician and case)
• For surgical options: bone quality concerns, uncontrolled medical comorbidities, or uncertainty that the SI joint is the dominant pain generator (selection criteria vary)

How it works (Mechanism / physiology)

Biomechanical principle

The SI joint is designed more for stability than for large motion. Its job is to provide a stable connection between the spine and pelvis while allowing subtle movement that helps dissipate forces. Stability comes from a combination of:

• Joint shape and cartilage surfaces
• Strong supporting ligaments (including posterior sacroiliac ligament complexes and related pelvic ligaments)
• Muscle forces that tension the pelvis and trunk (often described as “force closure” in biomechanics)

Relevant anatomy and tissues involved

Each SI joint sits between:

• The sacrum (the triangular bone at the base of the spine)
• The ilium (the large pelvic bone on each side)

The joint region includes a combination of articular surfaces and ligamentous structures. The front (anterior) portion is often described as more joint-like, while the back (posterior) portion is more ligament-dominant. Nearby structures that can confuse the picture include the lumbar facet joints, intervertebral discs, hip joint, gluteal muscles, piriformis region, and multiple pain-sensitive ligaments.

How SI joint pain is thought to occur

SI joint–related pain is generally discussed in terms of:

• Inflammation within or around the joint
• Degenerative change (wear-related changes can occur with age and loading)
• Ligament strain or overload affecting supporting structures
• Altered mechanics after injury, pregnancy-related ligament changes, or adjacent spine/hip conditions (varies by case)

Because symptoms overlap with other conditions, many clinicians rely on a combination of history, exam maneuvers, and, when appropriate, diagnostic injections to improve confidence that the SI joint is the primary pain generator.

Onset, duration, and reversibility

The SI joint itself is an anatomic structure, not a treatment, so “onset” and “duration” do not apply in the way they would for a medication. For SI joint–targeted interventions (like injections or procedures), the timing and durability of symptom change can vary widely by clinician and case, underlying diagnosis, and the specific intervention used.

SI joint Procedure overview (How it’s applied)

The SI joint is not a single procedure. In clinical practice, “SI joint evaluation” typically refers to a workflow that may include examination, testing, and sometimes targeted interventions.

A general overview often looks like this:

1. Evaluation / exam
   – Review of symptoms (location, triggers, functional limits) and relevant history (trauma, pregnancy, inflammatory disease risk, prior spine/hip issues)
   – Physical exam assessing the lumbar spine, hips, gait, neurologic status, and pelvic/SI joint provocative maneuvers
   – Consideration of overlapping diagnoses, because SI joint pain can mimic other conditions

2. Preparation (if testing or procedures are considered)
   – Imaging may be used to rule out alternative causes or to evaluate the pelvis/lumbar spine (choice varies by clinician and case)
   – If an injection is planned, clinicians typically review medications, allergies, and bleeding risk and discuss expected goals and limitations

3. Intervention / testing
   – Diagnostic injection: anesthetic is placed near or within the SI joint under imaging guidance to see whether pain temporarily improves
   – Therapeutic injection: may include an anti-inflammatory medication, often paired with local anesthetic (details vary)
   – Other interventions may be considered for selected cases, such as radiofrequency-based procedures targeting pain-transmitting nerves (techniques vary)

4. Immediate checks
   – Monitoring for short-term side effects and documenting symptom response, particularly after diagnostic blocks
   – Reassessment of function and pain patterns over the short term (timing varies)

5. Follow-up
   – Re-evaluation of diagnosis and function, including whether the response supports SI joint involvement
   – Discussion of next steps, which may include rehabilitation strategies, additional diagnostic clarification, or procedural options depending on the case

Types / variations

Because SI joint is an anatomic term, “types” usually refers to clinical contexts and management pathways rather than different devices alone.

Common variations include:

• SI joint dysfunction (mechanical pain pattern): a broad, sometimes inconsistently used term that may describe pain thought to relate to joint mechanics or ligament strain
• Degenerative SI joint pain: symptoms attributed to wear-related changes; often discussed in older adults or after altered biomechanics (varies by case)
• Inflammatory sacroiliac involvement: sacroiliac-region inflammation can occur in certain inflammatory arthritides; evaluation often includes labs and imaging based on clinical suspicion
• Post-traumatic SI joint pain: following falls, motor vehicle collisions, or pelvic ring injuries
• Pregnancy/postpartum pelvic girdle pain: may involve the SI joint region, with multiple contributing factors (varies widely)

Interventional variations commonly discussed include:

• Diagnostic vs therapeutic injections
• Intra-articular vs periarticular injection targets (approach varies by clinician and anatomy)
• Minimally invasive SI joint fusion techniques: multiple implant designs and approaches exist; outcomes and indications vary by material and manufacturer and by patient selection

Pros and cons

Pros:

• Helps clinicians localize a potential pain source in complex low back/hip/buttock symptom patterns
• Provides an anatomic framework for discussing pelvic load transfer and stability
• Diagnostic injections can add clarity when exam and imaging are inconclusive (results can still be imperfect)
• Therapeutic options range from rehabilitation-focused care to image-guided procedures, depending on severity and diagnosis
• SI joint–focused evaluation can reduce missed alternative diagnoses by encouraging systematic hip/spine/pelvis assessment

Cons:

• Symptoms commonly overlap with lumbar spine, hip joint, and soft-tissue conditions, complicating diagnosis
• Physical exam tests are not perfectly specific; clinicians often need multiple converging findings
• Imaging findings may not match symptoms; “abnormal” changes can be present without pain (and vice versa)
• Interventions (injections or procedures) carry risks and may not provide lasting benefit for every patient
• Terminology such as “SI joint dysfunction” can be used differently across clinicians and settings

Aftercare & longevity

Aftercare depends on what “SI joint care” means in a given case—evaluation only, rehabilitation, injection-based treatment, or surgery.

In general, outcomes and longevity are influenced by:

• Accuracy of diagnosis: whether the SI joint is truly the main pain generator versus a coexisting issue
• Condition type and severity: inflammatory vs degenerative vs post-traumatic patterns can behave differently
• Rehabilitation participation: many care plans emphasize progressive strength, movement tolerance, and load management (specific programs vary)
• Activity demands: occupational lifting, sport requirements, and prolonged standing can change symptom patterns
• Coexisting conditions: hip osteoarthritis, lumbar spine degeneration, osteoporosis, and systemic inflammatory disease can affect recovery trajectories
• For injections: response duration varies by clinician and case, medication used, and whether pain is driven by inflammation versus other mechanisms
• For surgical fusion: longevity relates to patient selection, implant type, bone quality, and healing biology; details vary by material and manufacturer

Follow-up is commonly used to reassess function, confirm or refine the diagnosis, and decide whether the plan should be continued, modified, or escalated.

Alternatives / comparisons

Because SI joint symptoms overlap with multiple regions, alternatives often focus on different diagnoses and different treatment intensity levels.

High-level comparisons commonly include:

• Observation/monitoring vs active treatment

• When symptoms are mild or improving, clinicians may emphasize reassessment over time and basic functional tracking rather than immediate procedures.

• Rehabilitation-focused care vs injections

• Rehabilitation aims to improve load tolerance, strength, and movement strategies across the trunk/hip/pelvis.

• Injections may be used to support diagnosis (diagnostic blocks) or to reduce inflammation-related pain when present (therapeutic injections). The best sequence varies by clinician and case.

• Medication-based symptom management vs procedures

• Non-procedural options may be used to manage discomfort while function is addressed through activity modification and rehabilitation.

• Procedural options are typically considered when symptoms persist, diagnostic confidence is higher, and conservative measures have not met goals (varies by case).

• Radiofrequency-based procedures vs fusion surgery

• Radiofrequency approaches target pain signaling pathways and are typically considered non-fusion interventions; techniques and candidacy vary.

• Fusion procedures aim to reduce painful motion by stabilizing the joint in carefully selected patients; they involve different risks and recovery expectations than injections.

• SI joint vs hip vs lumbar spine workup

• Hip joint disorders often cause groin/anterior thigh pain and limited hip range of motion (though patterns vary).
• Lumbar causes may include nerve symptoms (radiating pain, numbness, weakness) or pain linked to spine loading.
• SI joint–related pain is often described around the posterior pelvis/buttock region, but overlap is common, so clinicians typically evaluate all three regions.

SI joint Common questions (FAQ)

Q: Where is SI joint pain usually felt?
Pain attributed to the SI joint is often described in the buttock or posterior pelvic area and may be one-sided. Some people report pain that seems to travel into the upper thigh, but patterns overlap with hip and lumbar conditions. Because location alone is not definitive, clinicians combine history, exam, and sometimes targeted testing.

Q: How do clinicians diagnose SI joint problems?
Diagnosis is usually based on a combination of symptom history, physical exam maneuvers, and assessment of the hip and lumbar spine to rule out other causes. Imaging may help exclude fractures or other conditions but may not “prove” the SI joint is the source. In some cases, an image-guided diagnostic injection is used to see whether numbing the joint changes pain in the short term.

Q: Can imaging (X-ray, MRI, CT) confirm the SI joint is the cause of pain?
Imaging can show anatomy and certain changes, but findings do not always match symptoms. Some people have imaging changes without pain, and others have pain with minimal visible change. The choice of imaging and how it is interpreted varies by clinician and case.

Q: What is the difference between a diagnostic SI joint injection and a therapeutic injection?
A diagnostic injection primarily uses local anesthetic to test whether pain improves temporarily when the SI joint region is numbed. A therapeutic injection typically aims to reduce inflammation-related pain for a longer period and may include an anti-inflammatory medication. Response and duration vary by clinician and case.

Q: How long do SI joint injection results last?
Duration varies widely and depends on the underlying cause, the medication used, and whether the SI joint is the main pain generator. Some people notice only short-term change, while others report longer symptom reduction. Clinicians often use the pattern of response—not just duration—to guide next steps.

Q: Is SI joint treatment generally safe?
Most commonly used approaches have established safety practices, especially when image guidance and appropriate screening are used. However, no procedure is risk-free, and risks vary depending on the intervention (for example, injection vs surgery) and individual health factors. A clinician typically reviews expected benefits, limitations, and potential complications in context.

Q: Will I be able to drive or work after an SI joint injection or procedure?
Recommendations vary by clinician, procedure type, and how you feel afterward. Temporary numbness, soreness, or medication effects may affect driving or work tasks for a period of time. Many clinics provide procedure-specific restrictions as part of standard after-visit instructions.

Q: Does SI joint fusion permanently eliminate SI joint motion?
Fusion procedures aim to stabilize the joint and reduce painful motion, but the exact biomechanical result can vary with technique, implant design, and healing. People may still have pain from other nearby structures even if the SI joint is stabilized. Candidacy and expected outcomes are individualized.

Q: What does SI joint care typically cost?
Costs vary substantially based on geography, insurance coverage, facility setting, and whether care involves imaging, physical therapy, injections, or surgery. Even within the same category (for example, injections), pricing can differ by technique and setting. A clinic or insurer can usually provide the most accurate estimate for a specific plan of care.