If you have persistent lower back or buttock pain that has not been explained by a disc herniation, spinal stenosis, or any other clearly identified spinal problem, there is a good chance your sacroiliac joint has never been seriously evaluated. The SI joint is responsible for somewhere between 15 and 30 percent of chronic lower back pain in the general population — and yet it is one of the most consistently overlooked pain generators in spine care. Patients sometimes spend years being treated for the wrong condition before someone finally focuses on the joint at the base of the spine connecting the sacrum to the pelvis.

In this article, I want to walk you through the anatomy, the causes, the symptoms, and — most importantly — the full spectrum of treatment options for sacroiliac joint dysfunction, from conservative care and injections all the way through minimally invasive surgical fusion.

What Is the Sacroiliac Joint?

The sacroiliac joint — more commonly called the SI joint — is the joint connecting the sacrum (the large triangular bone at the base of your spine) to the ilium (the large, wing-shaped bone on each side of your pelvis). You actually have two SI joints, one on each side, and together they function as the primary load-transfer mechanism between your spine and your legs. Every time you walk, climb stairs, or stand up from a chair, compressive and shear forces are transmitted through the SI joints.

Unlike most joints in the body, the SI joint is designed primarily for stability, not mobility. It has a small range of motion — roughly two to four degrees of rotation — and is reinforced by some of the strongest ligaments in the human body. This is by design. The joint needs to be stiff enough to transmit force efficiently, but it also needs just enough give to accommodate movement.

When the SI joint is working properly, you never think about it. When it is not — when it becomes inflamed, hypermobile, or stiffened from degenerative changes — it can produce pain that mimics a disc herniation, hip pathology, or piriformis syndrome closely enough to lead even experienced clinicians in the wrong direction.

What Causes SI Joint Dysfunction?

Several distinct mechanisms can disrupt normal SI joint function:

Degenerative Joint Disease

Like any synovial joint, the SI joint is subject to degenerative arthritis over time. As the cartilage lining the joint wears down, the surfaces become irregular, inflammation develops, and pain results. This is the most common cause of SI joint pain in older adults and frequently occurs alongside lumbar degenerative disc disease — which makes the diagnostic picture more complicated.

Trauma

A fall onto one side, a motor vehicle accident, or a sudden impact to the pelvis can damage the ligaments that stabilize the SI joint, leaving it hypermobile and painful. Patients sometimes describe the onset of their pain with precision: "It started after I slipped off a ladder" or "It began after my car accident three years ago." This history is important and should not be dismissed.

Pregnancy and Postpartum Changes

During pregnancy, the hormone relaxin causes the pelvic ligaments to loosen in preparation for childbirth. This can allow excessive SI joint motion, leading to significant pain during pregnancy and sometimes persisting postpartum. SI joint dysfunction is one of the most common musculoskeletal complaints during and after pregnancy.

Prior Lumbar Fusion

This is particularly important for patients who have already had lumbar spine surgery. When one or more lumbar levels are fused, the forces that would normally be distributed across multiple spinal segments are redirected — and a significant portion of that increased load falls on the SI joints. Studies show that SI joint degeneration occurs in roughly 75 percent of patients within five years of a lumbar fusion, and symptomatic SI joint pain develops in a meaningful subset of those patients. If you have had a lumbar fusion and are developing new-onset buttock or lower back pain, SI joint evaluation should be near the top of the differential diagnosis.

Inflammatory Arthropathies

Conditions such as ankylosing spondylitis, psoriatic arthritis, and reactive arthritis can cause inflammatory involvement of the SI joints. These conditions have a distinct presentation and management pathway and are important to identify early.

Symptoms — And Why SI Joint Pain Is So Often Missed

The classic presentation of SI joint dysfunction is pain centered over the posterior superior iliac spine (PSIS) — that bony prominence you can feel just beneath the skin on either side of the lower back, often marked by a small dimple. Patients sometimes point directly to this area with one finger, which is actually a fairly specific clinical sign. The pain can radiate into the buttock, the groin, and down the back of the thigh — sometimes as far as the knee, though rarely below it.

Common complaints include:

The reason SI joint pain is so frequently missed is that it can feel almost identical to a herniated disc or hip arthritis. Radiating pain down the buttock and thigh is easy to attribute to a nerve root problem, and many patients undergo MRI imaging of the lumbar spine looking for a disc herniation or nerve compression that does not fully explain the clinical picture. The key distinction is that true nerve root compression from a disc herniation typically produces pain below the knee with specific dermatomal patterns, whereas SI joint pain tends to stay above the knee and does not follow a clean dermatomal distribution.

How We Diagnose SI Joint Dysfunction

Diagnosing SI joint dysfunction requires a combination of physical examination findings and, ultimately, a diagnostic injection. There is no single MRI finding or X-ray finding that reliably confirms the SI joint as the pain source — imaging is useful for ruling out other problems and for characterizing the degree of degeneration, but the diagnosis is fundamentally clinical and interventional.

Physical Examination

I use a battery of provocative maneuvers specifically designed to stress the SI joint and reproduce the patient's pain. No single test is definitive, but when three or more of the following are positive, the sensitivity and specificity for SI joint pathology are quite high:

Imaging

Plain X-rays can show joint space narrowing, sclerosis, and arthritic changes in the SI joint. CT scan provides better bony detail. MRI is useful for detecting active inflammation (edema in the subchondral bone — called a "bone marrow edema pattern") and for ruling out sacral stress fractures and inflammatory spondyloarthropathy. I typically start with standing X-rays of the pelvis and lumbar spine, followed by MRI of the sacroiliac joints when the clinical picture warrants it.

Diagnostic Injection — The Gold Standard

The definitive diagnostic test is an image-guided injection of local anesthetic directly into the SI joint. This is typically performed under fluoroscopic or CT guidance by an interventional pain management specialist. If the injection provides significant, temporary relief of your characteristic pain — typically defined as at least 75 percent improvement for the duration of the anesthetic — it confirms that the SI joint is the primary pain generator. This confirmation is essential before considering any surgical intervention.

The diagnostic injection is not optional before surgery. It is the critical step that distinguishes SI joint pain from adjacent pain generators. I will not recommend surgical fusion without clear documentation of a positive diagnostic injection response.

Treatment Options for Sacroiliac Joint Dysfunction

Management of SI joint pain follows a logical stepwise progression — starting with the least invasive options and escalating based on the patient's response. The good news is that many patients respond well to conservative and interventional treatment without ever needing surgery.

Conservative Treatment

The first line of treatment for SI joint dysfunction combines activity modification, physical therapy, and anti-inflammatory medications. Physical therapy focuses on strengthening the muscles that stabilize the SI joint — specifically the gluteal muscles, core stabilizers, and hip abductors — and on correcting movement patterns that load the joint asymmetrically. Manual therapy techniques, including joint mobilization, can also provide meaningful relief in the acute and subacute phases.

An SI joint belt or sacral support belt can help during flare-ups by compressing and stabilizing the pelvis. This is particularly useful for patients with hypermobility-related pain, including postpartum SI joint dysfunction.

NSAIDs (such as ibuprofen or naproxen) reduce joint inflammation and are appropriate as a first-line pharmacologic measure. I am cautious with long-term NSAID use given the cardiovascular and gastrointestinal risks, but for acute flares, a short course is reasonable and often effective.

SI Joint Injections

When conservative treatment does not provide lasting relief, corticosteroid injections into the SI joint are the next step. These are performed under image guidance — fluoroscopy or CT — to confirm accurate needle placement within the joint. The injection delivers a potent anti-inflammatory steroid directly to the pain source, often providing significant relief lasting weeks to months.

SI joint injections serve two purposes: therapeutic (pain relief) and diagnostic (confirming the joint as the pain source). For patients who receive substantial but temporary relief from injections, this confirms that further, more durable treatment is indicated. Injections can be repeated, but most patients who are going to respond will experience diminishing returns after two to three treatments, at which point a different approach is warranted.

Radiofrequency Ablation (RFA)

For patients who have confirmed SI joint pain with injection response but are not candidates for or not interested in surgery, radiofrequency ablation is an excellent intermediate option. RFA uses heat generated by radiofrequency energy to interrupt the sensory nerve fibers supplying the SI joint — specifically the lateral branches of the dorsal sacral nerve roots (S1-S3) and the L5 dorsal ramus.

The procedure is performed under fluoroscopic guidance and is done as an outpatient procedure. The pain relief from SI joint RFA typically lasts 9 to 18 months, after which the nerves regenerate and the procedure can be repeated. It is not a permanent solution, but it can be an excellent bridge for patients who want to avoid surgery, and it is particularly useful for patients who are not optimal surgical candidates due to medical comorbidities.

Minimally Invasive SI Joint Fusion

When a patient has confirmed SI joint dysfunction, has failed conservative and interventional treatment, and demonstrates a clear positive response to diagnostic injection, minimally invasive SI joint fusion is the most durable and definitive treatment option. The surgery stabilizes the SI joint by placing implants across the joint to eliminate the pathologic motion that is driving the pain.

Modern minimally invasive SI fusion techniques represent a significant advance over older open surgical approaches. Using a small lateral incision over the gluteal region, implants are placed under fluoroscopic guidance directly across the SI joint. The procedure typically takes 30 to 45 minutes, involves minimal blood loss, and is performed as an outpatient or single-night procedure in most cases.

The technology in this space has evolved considerably. Newer implant designs aim to maximize surface area contact and promote bone ingrowth across the joint for long-term fixation. As a consultant for emerging SI fusion technologies, I evaluate these systems closely — the design of the implant matters, particularly the geometry that allows bone ingrowth and the mechanism for engaging the dense cortical and cancellous bone of the ilium and sacrum. The goal is durable, biologic fixation that holds long-term without the risk of implant migration.

Patient outcomes after minimally invasive SI joint fusion have been well-studied. Multiple prospective clinical trials have demonstrated significant improvements in pain scores, functional status, and quality of life at two- and five-year follow-up. Roughly 80 to 85 percent of appropriately selected patients report meaningful, sustained pain relief after surgery. The key phrase there is "appropriately selected" — patient selection is everything with SI joint fusion, which is why the diagnostic injection is non-negotiable before proceeding.

When Is SI Joint Fusion the Right Choice?

I recommend considering SI joint fusion when the following criteria are met:

This is also an important consideration for patients who have had prior lumbar fusion and are developing adjacent SI joint degeneration. Extending fixation across the SI joint at the time of a lumbar fusion revision — or addressing it as a staged procedure — can provide substantial relief in this population.

Recovery After SI Joint Fusion

Recovery from minimally invasive SI joint fusion is generally straightforward. Most patients are weight-bearing with a walker or crutches on the day of surgery and transition to full weight-bearing without assistive devices over the first two to four weeks. I typically restrict high-impact activities for six to twelve weeks while the joint is actively healing.

Pain relief often begins within the first few weeks, though full recovery and maximum benefit are typically realized at three to six months as the bone ingrowth matures and the joint stabilizes fully. Physical therapy is an important part of recovery — rebuilding the gluteal and core musculature that has been inhibited by chronic pain accelerates functional recovery significantly.

The Bottom Line

Sacroiliac joint dysfunction is common, clinically underdiagnosed, and very treatable when identified correctly. If you have persistent lower back, buttock, or pelvic pain that has not been fully explained by spinal pathology, the SI joint deserves evaluation. The diagnostic pathway — provocative examination, imaging, and confirmatory injection — is straightforward, and the treatment ladder from physical therapy through fusion is well-established with solid outcomes data.

The most important thing is getting the diagnosis right. Pain in the lower back and pelvis has many potential sources, and attributing it to the wrong structure leads to treatments that do not work. A careful evaluation is the foundation of effective treatment.

If you are dealing with persistent lower back or buttock pain and want a thorough evaluation, I welcome you to schedule a consultation. You can reach Keystone Spine & Pain Management at (484) 509-0840 or visit our contact page to request an appointment at our office in Wyomissing, PA.