Lower back pain is often blamed on a herniated disc, arthritis, sciatica, or muscle strain. However, one commonly overlooked source of pain is the sacroiliac joint, also known as the SI joint. When this joint becomes inflamed, irritated, unstable, or painful, it can cause discomfort in the lower back, buttocks, hips, pelvis, groin, and sometimes the legs.
This condition is often referred to as sacroiliitis when inflammation is present. A broader term, sacroiliac joint dysfunction, may be used when pain is related to abnormal joint movement, degeneration, instability, irritation, or other mechanical problems. Because SI joint pain can mimic lumbar spine conditions, many patients struggle to identify the true source of their symptoms.
The good news is that many cases of sacroiliitis and sacroiliac joint pain can be treated without surgery. When conservative care does not provide enough relief, minimally invasive sacroiliac joint surgery, most commonly SI joint fusion, may be an option for carefully selected patients.
What Is the Sacroiliac Joint?
The sacroiliac joints are located where the sacrum, the triangular bone at the base of the spine, connects to the ilium, which is part of the pelvis. There is one SI joint on each side of the body.
These joints play an important role in stability and movement. They help transfer weight and force between the upper body and the legs while absorbing stress during walking, standing, bending, lifting, and twisting. The SI joints normally move only a small amount, but even subtle changes in motion, inflammation, or stability can create significant pain.
What Is Sacroiliitis?
Sacroiliitis is inflammation of one or both sacroiliac joints. This inflammation can cause pain and stiffness in the lower back, buttocks, hips, and pelvis. In some cases, discomfort may spread into the groin, thigh, or leg, which is one reason sacroiliitis is sometimes mistaken for sciatica or a lumbar disc problem.
Sacroiliitis may develop because of arthritis, injury, pregnancy-related changes, infection, inflammatory disease, or increased stress on the SI joint. Some patients experience a gradual onset of pain, while others notice symptoms after a fall, car accident, surgery, childbirth, or another specific event.
Sacroiliitis vs. Sacroiliac Joint Dysfunction
Although these terms are often used together, they do not mean exactly the same thing.
Sacroiliitis specifically refers to inflammation of the sacroiliac joint.
Sacroiliac joint dysfunction is a broader term that may describe pain caused by abnormal joint movement, instability, degeneration, irritation, or mechanical stress. A patient may have SI joint dysfunction with or without obvious inflammation.
For patients, the most important issue is not the label itself, but whether the SI joint is truly the source of pain. Once the pain generator is identified, treatment can be more precise and effective.
Common Symptoms of Sacroiliitis and SI Joint Pain
Sacroiliitis and SI joint dysfunction can cause symptoms that range from mild discomfort to severe, activity-limiting pain. Many patients describe the pain as deep, aching, sharp, or stabbing near one side of the lower back or buttock.
Common symptoms may include:
- Lower back pain, often on one side
- Buttock pain or tenderness
- Hip or pelvic discomfort
- Groin pain
- Pain that spreads into the thigh or leg
- Stiffness in the lower back, hips, or pelvis
- Pain when standing up from a seated position
- Pain with stairs, walking, or prolonged standing
- Discomfort after sitting for long periods
- Pain when rolling over in bed or lying on the affected side
Pain from the SI joint can sometimes travel into the leg, but this does not always mean the patient has a pinched nerve. SI joint pain can mimic sciatica, which is why a careful diagnosis is so important.
What Causes Sacroiliitis and Sacroiliac Joint Pain?
SI joint pain can develop for many different reasons. In some patients, inflammation is the primary problem. In others, pain may be related to joint degeneration, abnormal mechanics, instability, trauma, or increased stress across the pelvis.
Arthritis
Arthritis is one of the most common causes of sacroiliac joint pain. Inflammatory forms of arthritis can affect the SI joints and may cause pain, stiffness, and reduced mobility. Degenerative arthritis can also contribute to SI joint irritation over time.
Injury or Trauma
A fall, car accident, sports injury, or direct impact to the pelvis can irritate or damage the sacroiliac joint. Even when no fracture occurs, trauma can disrupt the normal mechanics of the SI joint and lead to ongoing pain.
Pregnancy and Postpartum Changes
During pregnancy, the body naturally produces hormones that allow ligaments to loosen in preparation for childbirth. This increased flexibility, combined with changes in posture, weight distribution, and pelvic mechanics, can place additional strain on the SI joints. Some patients continue to experience SI joint pain after delivery.
Prior Lumbar Fusion Surgery
SI joint pain is a recognized source of new or persistent lower back pain in some patients after lumbar fusion. When motion is reduced in one area of the spine, force may shift to nearby structures, including the sacroiliac joints. This does not happen to every patient, but it is an important consideration when evaluating pain after spine surgery.
Leg Length Difference or Abnormal Gait
A difference in leg length, altered walking pattern, scoliosis, or uneven mechanics can increase stress across one SI joint more than the other. Over time, this may contribute to irritation, inflammation, or dysfunction.
Infection
Although uncommon, infection can cause sacroiliitis. This is a more serious condition and may require urgent medical evaluation, especially when pain is accompanied by fever, chills, unexplained illness, or other concerning symptoms.
How Sacroiliitis Is Diagnosed
Diagnosing sacroiliitis and SI joint dysfunction can be challenging because symptoms often overlap with lumbar spine disorders, hip conditions, muscle pain, and nerve-related pain. A proper diagnosis usually begins with a detailed medical history and physical examination.
A spine specialist may evaluate:
- Where the pain is located
- Whether symptoms are one-sided or both-sided
- What activities worsen or relieve pain
- Whether pain spreads into the hip, groin, thigh, or leg
- Prior injuries, surgeries, pregnancies, or inflammatory conditions
- Hip, spine, and pelvic motion
- Tenderness around the SI joint
- Strength, reflexes, and nerve-related symptoms
During the exam, the physician may use specific movements or stress tests designed to reproduce pain from the sacroiliac joint. These tests are helpful, but no single physical exam maneuver can prove the diagnosis by itself.
Imaging studies such as X-rays, CT scans, or MRI may also be used. These tests can help identify arthritis, inflammation, fracture, infection, degeneration, or other possible causes of pain. However, imaging can be normal even when the SI joint is painful. Likewise, abnormal imaging does not always mean the SI joint is the main source of symptoms.
For this reason, diagnosis often depends on the full clinical picture, including symptoms, exam findings, imaging results, and response to targeted treatment.
Diagnostic Sacroiliac Joint Injections
One of the most useful tools for evaluating SI joint pain is an image-guided sacroiliac joint injection. During this procedure, a numbing medication, often combined with an anti-inflammatory medication, is placed directly into the SI joint using imaging guidance for accuracy.
If the injection significantly reduces the patient’s typical pain, it provides strong evidence that the SI joint is a major pain generator. This does not mean the injection is a perfect test, but it can be very helpful when combined with the rest of the evaluation.
Diagnostic injections can also help guide treatment decisions. For patients who are being considered for sacroiliac joint surgery, meaningful temporary relief after an SI joint injection is often an important part of confirming that the joint is truly responsible for the pain.
Non-Surgical Treatment for Sacroiliitis
Most patients with sacroiliitis or SI joint pain begin with conservative treatment. The goal is to reduce inflammation, improve stability, restore movement, and address any underlying condition contributing to symptoms.
Physical Therapy
Physical therapy is often one of the first treatments recommended. A structured program may focus on strengthening the core, hips, glutes, and pelvic stabilizing muscles. Stretching, posture correction, gait training, and movement retraining may also help reduce stress on the SI joint.
Physical therapy is especially important because SI joint pain is often influenced by how the pelvis, hips, and lower back move together. Improving strength and coordination can help reduce irritation and improve daily function.
Anti-Inflammatory Medication
Anti-inflammatory medications may help reduce pain and inflammation during flare-ups. These medications are not appropriate for every patient, especially those with certain stomach, kidney, heart, or bleeding-related conditions. Patients should follow medical guidance when using them.
Activity Modification
Temporarily modifying activities that aggravate symptoms can help calm the joint. This may include limiting prolonged sitting, heavy lifting, repetitive twisting, high-impact exercise, or movements that place uneven stress across the pelvis.
Activity modification does not mean avoiding movement altogether. In many cases, gentle motion, walking, and guided exercise are helpful. The key is finding the right balance between staying active and avoiding repeated irritation.
SI Joint Belt or Brace
Some patients may benefit from an SI joint belt or brace, particularly when instability or pregnancy-related pelvic changes are suspected. These devices provide temporary external support around the pelvis and may help reduce painful motion during daily activities.
An SI belt is not a cure for sacroiliitis, but it may be a useful part of a broader treatment plan for selected patients.
Image-Guided SI Joint Injections
Corticosteroid injections may help reduce inflammation and provide temporary pain relief. In some patients, relief may last for weeks or months. In others, the benefit may be shorter. The response varies depending on the underlying cause of pain and the patient’s overall condition.
SI joint injections may be used both diagnostically and therapeutically. When an injection provides meaningful relief, it can help confirm the source of pain while also giving the patient an opportunity to participate more comfortably in rehabilitation.
Radiofrequency Ablation
Radiofrequency ablation, also called radiofrequency denervation, may be considered for selected patients. This minimally invasive procedure uses controlled heat to reduce pain signals from nerves that supply the SI joint region.
Radiofrequency ablation does not fuse or structurally change the joint. Relief varies from patient to patient and is not necessarily permanent, but it may help some patients manage chronic SI joint pain without surgery.
When Is Sacroiliac Joint Surgery Considered?
Surgery is not usually the first treatment for sacroiliitis or sacroiliac joint dysfunction. It is generally considered only when pain is persistent, function-limiting, and clearly traced to the SI joint after appropriate nonsurgical treatments have not provided enough relief.
A patient may be evaluated for sacroiliac joint surgery if they have:
- Chronic SI joint pain that interferes with daily life
- Pain that has not improved with conservative care
- Symptoms and exam findings consistent with SI joint pain
- Imaging used to rule out other major causes of symptoms
- Meaningful temporary relief after a diagnostic SI joint injection
- No better explanation for the pain from the lumbar spine, hip, or another condition
- Difficulty walking, standing, working, sleeping, or performing normal activities
Because SI joint pain can overlap with other conditions, surgical candidacy should be based on a careful, multi-step evaluation. A diagnostic injection response alone is not enough. The full clinical picture should support the SI joint as the primary pain source.
What Is Sacroiliac Joint Fusion?
Sacroiliac joint fusion, also called SI joint fusion, is a surgical procedure designed to stabilize the sacroiliac joint. The goal is to reduce painful motion in the joint by encouraging the sacrum and ilium to heal together into one more stable structure.
In a minimally invasive SI joint fusion, the surgeon typically uses small incisions and imaging guidance to place implants across the sacroiliac joint. These implants help stabilize the joint while bone gradually grows across the area over time.
SI joint fusion does not treat every type of lower back pain. It is intended for patients whose pain has been carefully traced to the sacroiliac joint and who have not responded well enough to nonsurgical treatment.
Minimally Invasive Sacroiliac Joint Surgery
Traditional open SI joint fusion required larger incisions and more tissue disruption. Today, many patients who need surgery may be candidates for a minimally invasive sacroiliac joint fusion.
Minimally invasive SI joint surgery is designed to stabilize the joint while limiting disruption to surrounding tissues. Compared with traditional open surgery, a minimally invasive approach may be associated with:
- Smaller incisions
- Less muscle disruption
- Reduced blood loss
- Shorter operative time in many cases
- Faster early mobility for some patients
- Outpatient or short-stay surgical options, depending on the patient and surgical setting
- Potentially fewer wound-related issues than open surgery
These are possible advantages, not guarantees. Outcomes vary based on the patient’s diagnosis, anatomy, health, surgical technique, recovery process, and whether the SI joint is truly the main source of pain.
What Happens During SI Joint Fusion Surgery?
The exact technique may vary depending on the surgeon, implant system, patient anatomy, and individual treatment plan. In general, minimally invasive SI joint fusion involves several key steps.
The patient is positioned to allow access to the SI joint, usually lying face down. The surgeon uses imaging guidance to identify the correct location and pathway. A small incision is made near the side of the pelvis. Specialized instruments are used to prepare the area, and implants are placed across the sacroiliac joint to stabilize it.
Over time, the goal is for bone to grow across the joint. This fusion process is intended to reduce painful motion and improve stability.
Recovery After Sacroiliac Joint Surgery
Recovery after sacroiliac joint surgery varies from patient to patient. Factors such as age, bone health, overall medical condition, surgical technique, physical demands, and the duration of symptoms can all affect the recovery process.
Some patients may be able to return home the same day or after a short stay, depending on the surgical setting and their individual needs. During early recovery, patients may be asked to limit weight-bearing, use crutches or a walker, avoid bending and twisting, and follow specific postoperative instructions.
Physical therapy may be recommended once the surgeon determines it is appropriate. Rehabilitation often focuses on restoring safe movement, improving strength, protecting the fusion area, and gradually returning to normal activities.
Healing after fusion is gradual. Some patients notice improvement relatively early, while others improve more slowly over several months. Full recovery and bone healing can take time, and following postoperative instructions is important for supporting the best possible outcome.
Potential Benefits of Sacroiliac Joint Surgery
For the right patient, sacroiliac joint fusion may help reduce pain caused by abnormal or painful SI joint motion. Potential benefits may include:
- Improved pelvic stability
- Reduced lower back or buttock pain
- Improved walking and standing tolerance
- Better ability to perform daily activities
- Improved sleep and quality of life when pain improves
- Possible reduction in pain medication use under medical supervision
These benefits are not guaranteed. Some patients have more than one source of pain, such as lumbar spine disease, hip arthritis, nerve irritation, or muscular dysfunction. In those cases, SI joint surgery may improve pain coming from the SI joint but may not eliminate every symptom.
Risks and Considerations
Like any surgery, sacroiliac joint fusion has potential risks. These may include infection, bleeding, nerve irritation, implant-related problems, incomplete fusion, continued pain, blood clots, or the need for additional treatment.
Another important consideration is diagnostic accuracy. SI joint fusion should not be performed simply because imaging shows arthritis, degeneration, or inflammation. Many people have imaging changes that may not be the true cause of their pain. The diagnosis should be supported by symptoms, physical exam findings, imaging when appropriate, and response to diagnostic injections.
Sacroiliitis, Sciatica, and Lower Back Pain: Why Diagnosis Matters
Sacroiliitis and SI joint dysfunction can feel very similar to other common spine and orthopedic conditions. Patients may describe pain traveling into the buttock or leg and assume they have sciatica. Others may be told they have degenerative disc disease, spinal stenosis, or hip arthritis because those findings appear on imaging.
However, imaging findings do not always match the true source of pain. Many adults have age-related changes in the spine or hips that may not be causing symptoms. At the same time, SI joint pain can be missed if the evaluation focuses only on the lumbar discs and nerves.
A comprehensive evaluation helps determine whether pain is coming from the sacroiliac joint, lumbar spine, hip, muscles, ligaments, or a combination of structures. This distinction matters because the right treatment for a herniated disc may be very different from the right treatment for sacroiliac joint dysfunction.
Who May Be a Candidate for Minimally Invasive SI Joint Fusion?
A patient may be a candidate for minimally invasive sacroiliac joint fusion if they have chronic, function-limiting SI joint pain that has not responded to appropriate conservative care. Candidates typically have a diagnosis supported by medical history, physical examination, imaging when needed, and meaningful temporary relief from diagnostic SI joint injection.
Patients with infection, tumor-related instability, major pelvic trauma, complex deformity, or severe overlapping spine or hip conditions may require a different treatment approach. In some cases, open surgery or another procedure may be more appropriate.
For many patients with carefully confirmed SI joint dysfunction, however, minimally invasive SI joint fusion may offer a less disruptive surgical option than traditional open fusion.
Living With Sacroiliitis
Sacroiliitis can be frustrating because pain may come and go, shift location, or resemble other conditions. Some patients experience flare-ups after sitting too long, walking too far, climbing stairs, sleeping in certain positions, or standing for extended periods.
The most important step is identifying the true source of pain. Once the SI joint is recognized as a major contributor, treatment can become more focused. Many patients improve with conservative care, including physical therapy, medications, activity changes, bracing, injections, and other minimally invasive pain procedures.
For patients who continue to struggle despite these treatments, sacroiliac joint surgery may be worth discussing with a qualified spine specialist.
Sacroiliitis and Sacroiliac Joint Surgery in Florida
If you are dealing with chronic lower back, buttock, hip, groin, or pelvic pain, the sacroiliac joint may be part of the problem. At Total Spine and Orthopedics, our team evaluates lower back pain with a comprehensive approach designed to identify the true source of symptoms, not just the most obvious finding on imaging.
Treatment may begin with conservative options such as physical therapy, medication management, image-guided injections, or other minimally invasive pain procedures. When nonsurgical care is not enough and the SI joint has been carefully confirmed as the source of pain, minimally invasive sacroiliac joint surgery may be considered to help stabilize the joint and reduce painful motion.
Sacroiliitis is a common but often overlooked cause of lower back, buttock, hip, groin, and pelvic pain. Because it can closely resemble sciatica, disc problems, hip conditions, and other causes of lower back pain, accurate diagnosis is essential.
Most patients begin with nonsurgical care. For those with persistent, confirmed SI joint pain that does not respond to conservative treatment, minimally invasive sacroiliac joint fusion may offer a surgical option focused on improving stability and reducing pain from the joint.
If chronic lower back or pelvic pain is interfering with your daily life, a specialized evaluation can help determine whether the sacroiliac joint is involved and which treatment options may be appropriate.