Low back pain that isn't your spine: SI joint fusion

Your two sacroiliac joints sit where the iliac bones of the pelvis meet the sacrum — the triangular bone at the base of your spine, just above the tailbone. Every step you take transfers energy between your legs and torso through these joints. They're built for stability, not motion — but injury, deterioration, pregnancy, arthritis, prior lumbar fusion, or years of uneven load can make one hypermobile or degenerated.

The result is a distinctive pain pattern: one-sided low back and buttock pain, sometimes radiating into the hip, groin, or upper thigh. It flares when the joint is loaded — lifting, jogging, climbing stairs, rolling over in bed, or standing up from a chair.

Because the symptoms mimic lumbar disc problems and hip conditions, SI dysfunction hides in plain sight. The numbers say it shouldn't:

• Studies attribute 15–30% of chronic low back pain to the SI joint.
• Among patients with continued or new low back pain after a lumbar fusion, the SI joint is involved in up to 43% of cases.

That's why the SI joint should always be on the list when low back, hip, or pelvic pain is being worked up — especially when spine imaging doesn't explain the symptoms.

SI joint pain rarely announces itself by name. Patients usually describe some combination of the following — and if several sound familiar, the joint deserves a focused evaluation:

Diagnosis is systematic, not guesswork. Dr. Morton starts with provocative physical-exam maneuvers that stress the joint and reproduce your pain. X-rays, CT, and MRI follow — less to "see" SI dysfunction than to rule out the other causes of similar pain. His hip & knee focus means the mimics — hip arthritis and avascular necrosis — get caught, not missed. And because a disc problem can exist alongside SI dysfunction, finding one doesn't end the search.

The deciding test is an image-guided diagnostic injection. Local anesthetic is placed directly into the SI joint under X-ray or CT guidance, confirming exact needle placement. If your pain improves by at least 50% while the joint is numb, the SI joint is the source — or a significant contributor — to your low back, hip, or pelvic pain. If the injection barely helps, the SI joint is unlikely to be the culprit, and the workup looks elsewhere. Either way, you get an answer.

Most SI joint pain never needs surgery. Once the joint is confirmed as the pain source, treatment starts conservatively:

• Targeted physical therapy to stabilize the pelvis — available through the practice's PT teams in Honolulu and Kunia
• A pelvic (SI) belt to compress and support the joint
• Anti-inflammatory and oral medications
• Activity modification while the joint settles
• Therapeutic injections to calm inflammation

Many patients improve significantly with these measures. The honest caveat: relief isn't always permanent. Fusion enters the conversation when genuine SI-joint pain keeps returning despite months of well-executed conservative care — and when the diagnostic injection has clearly implicated the joint.

The iFuse Implant System® is designed for sacroiliac joint dysfunction caused by degeneration or disruption of the joint. Established indications include:

• Degenerative sacroiliitis — wear-and-tear breakdown of the joint
• SI joint disruption — instability after injury or from chronic overload
• Pregnancy-related SI pain that began during pregnancy or the peripartum period and has persisted more than 6 months after delivery
• Adjunct stabilization of the SI joint as part of a lumbar or thoracolumbar fusion
• Fractures involving the SI joint — acute, non-acute, and non-traumatic

In every case, candidacy also requires the fundamentals: a positive image-guided diagnostic injection and a genuine trial of conservative care. Like any surgical treatment, the iFuse Implant System carries risks; it may not be appropriate for all patients, and not all patients benefit. SI-BONE publishes full risk information at si-bone.com/risks, and Dr. Morton reviews the risks specific to you at your consultation.

Minimally invasive SI joint fusion places triangular titanium implants (the iFuse Implant System®) across the joint through an incision of about one inch, guided by intraoperative imaging. The triangular profile resists rotation immediately — no waiting for stability — and the porous titanium surface lets your bone grow onto the implants for lasting fixation. The procedure takes about an hour with minimal blood loss; most patients go home the same day or after one night, walking with protected weight-bearing that advances over the first weeks.

Dr. Morton has trained extensively in minimally invasive surgical (MIS) techniques, including the iFuse system from SI-BONE®, and his practice is one of the few in Hawai‘i offering surgeon-led care for this diagnosis — from workup through fusion — so patients don't bounce between specialists. If you've been told "your MRI looks fine" while your back still ruins your days, a consultation or a second opinion can finally put a name on the problem.

Implant choice matters, and here the data is unusually deep. The triangular iFuse design has been clinically evaluated more than any other SI joint fusion device:

• 100+ peer-reviewed publications document its safety, long-term effectiveness, and biomechanical and economic benefits
• It is the only SI joint fusion device supported by multiple prospective clinical studies, including two randomized controlled trials showing that iFuse treatment improves pain, patient function, and quality of life compared with non-surgical management
• Long-term prospective follow-up confirms durable clinical and radiographic outcomes

SI-BONE summarizes the published results at si-bone.com/results; the key studies are listed below.

1. Bernard TN, et al. Recognizing specific characteristics of nonspecific low back pain. Clin Orthop Relat Res. 1987;217:266–80.
2. Schwarzer AC, et al. The sacroiliac joint in chronic low back pain. Spine. 1995;20:31–7.
3. Maigne JY, et al. Results of sacroiliac joint double block and value of sacroiliac pain provocation tests in 54 patients with low back pain. Spine. 1996;21:1889–92.
4. Sembrano JN, et al. How often is low back pain not coming from the back? Spine. 2009;34:E27–32.
5. DePalma MJ, et al. Etiology of chronic low back pain in patients having undergone lumbar fusion. Pain Med. 2011;12:732–9.
6. Polly DW, et al.; INSITE Study Group. Two-year outcomes from a randomized controlled trial of minimally invasive sacroiliac joint fusion vs. non-surgical management for sacroiliac joint dysfunction. Int J Spine Surg. 2016;10:28.
7. Dengler J, et al. Randomized trial of sacroiliac joint fusion vs. conservative management for chronic low back pain attributed to the sacroiliac joint. J Bone Joint Surg Am. 2019;101(5):400–11.
8. Duhon B, et al.; SIFI Study Group. Triangular titanium implants for minimally invasive sacroiliac joint fusion: 2-year follow-up from a prospective multicenter trial. Int J Spine Surg. 2016;10:13.
9. Dengler J, et al.; INSITE, iMIA, and SIFI study groups. Predictors of outcome in conservative and minimally invasive surgical management of pain originating from the sacroiliac joint — a pooled analysis. Spine. 2017;42(21):1664–73.
10. Whang PG, et al. Long-term prospective clinical and radiographic outcomes after minimally invasive lateral transiliac sacroiliac joint fusion using triangular titanium implants. Med Devices (Auckl). 2019;12:411–22.
11. Patel V, et al. Prospective trial of sacroiliac joint fusion using 3D-printed triangular titanium implants: 24-month follow-up. Med Devices (Auckl). 2021;14:211–6.