If you have nagging pain deep in your lower back or one buttock that never seems to settle, you are not alone. Many people chase answers through discs, nerves, or muscles, yet the real source turns out to be the sacroiliac (SI) joint. This connection between the base of your spine and your pelvis is built for stability with just a hint of motion. When it becomes irritated or unstable, the pain can feel a lot like sciatica or a simple back strain, which is why it gets missed so often.

Studies consistently show that the SI joint accounts for 15 to 30 percent of chronic low back pain cases. That is a sizable number when you consider how common back pain is overall. The condition appears more frequently in certain groups, including women in the years following menopause, likely tied to natural changes in ligament stability and pelvic mechanics that can develop over time. Pregnancy can play a role earlier in life for some, and factors such as prior spine surgery, trauma, or even subtle leg-length differences can contribute in anyone.

The frustrating part is how easily this gets overlooked. Standard spine exams often focus on the discs and nerves, so patients bounce between treatments that never quite land. The good news is that once you identify the SI joint as the problem, the path forward is usually straightforward and supported by solid clinical evidence.

How physicians make the diagnosis

A careful doctor approaches this step by step, never rushing to imaging or injections. It starts with your story. They listen for clues: pain that worsens when you stand from sitting, climb stairs, or roll over in bed. Many people describe a deep, one-sided ache in the buttock that does not shoot down the leg quite like classic sciatica.

Next comes the hands-on exam. There is a cluster of five specific provocation tests (distraction, thigh thrust, compression, flexion, abduction, and external rotation [FABER], and Gaenslen). Each stresses the SI joint differently. If three or more of them reproduce your familiar pain, that combination carries strong diagnostic weight, roughly 91 percent sensitivity and solid specificity according to key studies.

Imaging helps rule out other issues. X-rays, magnetic resonance imaging (MRI), or computed tomography (CT) scans of the low back and pelvis check for disc problems, hip arthritis, fractures, or inflammatory conditions. Interestingly, the SI joint itself often looks fairly normal on these scans even when it is the pain generator, so the pictures mainly serve to clear the field.

The definitive step is the diagnostic injection. Using X-ray or CT guidance, the doctor places a small amount of numbing medicine, sometimes mixed with steroid, directly into the joint. If your pain drops dramatically, by 50 to 75 percent or more for several hours, that confirms the SI joint as the source. This test is both diagnostic and the beginning of treatment for many people.

A practical treatment plan that builds step by step

Treatment follows a logical ladder. Most people start with conservative care for 6 to 12 weeks: targeted physical therapy to improve core stability and pelvic alignment, possibly an SI belt for daytime support, and simple anti-inflammatory medication when appropriate. A surprising number find meaningful relief here alone.

When symptoms persist, the next reliable option is an SI joint steroid injection. Done under imaging guidance, it delivers corticosteroid and local anesthetic right where it is needed. Multiple studies, including systematic reviews and meta-analyses, show significant pain reduction, often cutting scores by half or more within weeks. Benefits frequently last 3 to 6 months or longer, with clear improvements in daily function and reduced disability. The procedure is low-risk and performed in an office or procedure suite.

For those whose relief fades after repeated injections, or who simply want a more durable solution, minimally invasive SI joint fusion offers a targeted fix. Modern techniques use small incisions and implants to stabilize the joint so it stops moving in ways that cause pain. Randomized controlled trials and long-term follow-up studies report impressive results: average pain drops of 50 points or more on a 100-point scale, substantial gains in function (Oswestry Disability Index improvements of 25 to 28 points), better quality of life, and high satisfaction rates that hold up for 2 to 5 years and beyond. Recovery is quicker than traditional open spine surgery, and complication rates remain low in properly selected patients.

Importantly, this is not a one-size-fits-all path. The key is confirming the diagnosis first so you are not treating the wrong structure.

Why this matters

Lower back pain is one of the leading causes of disability worldwide, yet the SI joint remains one of its hidden contributors. When patients and doctors overlook it, people endure months or years of frustration with treatments that never quite fit. Once identified, though, the options, from simple therapy and injections to fusion when needed, are practical and evidence-based.

If that deep buttock or lower-back ache has been hanging around despite other treatments, consider asking your physician or a spine specialist familiar with SI joint issues to evaluate it properly. A few targeted questions and tests can make all the difference. Many patients I hear from say the same thing once they finally get the right diagnosis: They wish they had checked it sooner.

Back pain does not have to be a mystery. Sometimes the answer sits right where the spine meets the pelvis, and the solutions are clearer than you might expect.

Kayvan Haddadan is a physiatrist and pain management physician, and president and medical director of Advanced Pain Diagnostic & Solutions, a multidisciplinary pain management practice in California that he founded in 2012. A physician and surgeon licensed by the Medical Board of California, he is double board-certified in pain medicine and physical medicine and rehabilitation. He is also certified in controlled substance registration through the DEA and serves as a qualified medical examiner through California’s Department of Industrial Relations Division of Workers’ Compensation.

Dr. Haddadan earned his Bachelor of Science degree from the College of Alborz in Tehran, Iran, and his medical degree from Shahid Beheshti University of Medical Sciences. He later received his Educational Commission for Foreign Medical Graduates certification in Philadelphia, completed an internship in medical surgery at Loyola University Medical Center’s Stritch School of Medicine in Illinois, and finished his residency in physical medicine and rehabilitation at the same institution. He completed his fellowship in pain medicine at California Pacific Medical Center’s Pacific Pain Treatment Center and also trained in medical acupuncture for physicians at the University of California, Los Angeles David Geffen School of Medicine.

Dr. Haddadan has contributed to 29 research publications across multiple specialties, including pain management, cardiology, pulmonology, endocrinology, gastroenterology, and infectious disease. His work has examined topics such as hyperlipidemia in high cardiovascular risk patients, hyperuricemia and gout management, type 2 diabetes and hypertension, chronic obstructive pulmonary disease and asthma therapies, influenza treatment, irritable bowel syndrome, and opioid related complications in chronic pain care. His research has also included clinical outcome studies in spinal cord stimulation and award-winning presentations on neuropathic pain management and neuromuscular disorders.