SI Joint Fusion

What Is Minimally Invasive Sacroiliac Joint Fusion?

The sacroiliac (SI) joint connects the sacrum — the triangular bone at the base of the spine — to the ilium of the pelvis on each side. When the SI joint becomes arthritic, unstable, or injured, it produces chronic low back, buttock, and leg pain that can be difficult to distinguish from lumbar spine problems. Surgical SI joint fusion eliminates painful motion across the joint and promotes bone growth to permanently stabilize it. The procedure is performed through a small minimally invasive incision and does not involve the lumbar spine, spinal cord, or hip joint. Your surgeon will select the approach — posterolateral transfixation or posterior — based on your anatomy, prior surgeries, and clinical needs.

Common Indications

• Sacroiliac joint degeneration or arthritis causing chronic low back or buttock pain
• SI joint disruption or instability following trauma, fall, or pregnancy
• SI joint pain confirmed by physical examination and diagnostic injection
• Failure of non-surgical treatment including injections and anti-inflammatory medications
• SI joint instability as part of adjacent segment disease after prior lumbar fusion

MIS SI joint fusion is supported by multiple randomized controlled trials demonstrating significant improvement in pain and function compared to non-surgical management. The INSITE and iMIA trials showed durable 2-year outcomes with high patient satisfaction. A meta-analysis of 57 cohorts and 2,851 patients confirmed significant pain and disability improvement across both lateral and posterior fusion techniques (Polly et al., Neurosurgery 2015; Sturesson et al., Eur Spine J 2017; Whang et al., Int J Spine Surg 2023).

Alternatives to Surgery

Surgery is one option for managing your condition. Not all alternatives are appropriate for every patient — their suitability depends on your specific diagnosis, symptoms, and prior treatment history.

• Sacroiliac joint corticosteroid injection — diagnostic and therapeutic
• Radiofrequency ablation (RFA) of SI joint nerves — for pain relief without fusion
• Physical therapy — SI joint stabilization exercises and pelvic girdle strengthening
• Chiropractic care — adjustment and manipulation of the SI joint
• Oral medications — anti-inflammatory agents, neuropathic pain medications
• Observation — accepting current level of function
• No surgery — with understanding that SI joint instability or degeneration may persist

Choosing not to have surgery is always an option. Your surgeon has discussed what you can expect if you decide not to proceed, including the possibility that symptoms may persist, worsen, or in some cases improve without surgery.

What Happens During Surgery

Your surgeon will select the approach based on your anatomy, prior surgeries, and clinical needs. Both are minimally invasive, performed under fluoroscopic (live X-ray) guidance.

Approach A — Posterolateral Transfixation (Most Common)

1. You are positioned face-down on the operating table.
2. A small incision (~3 cm) is made posterolaterally over the buttock, directly over the SI joint corridor.
3. Under continuous fluoroscopic guidance, a guide pin is advanced through the ilium, across the SI joint, and into the sacrum.
4. The implant channel is sequentially prepared along this trajectory.
5. Two or three triangular titanium implants are seated across the SI joint in a triangular pattern, providing immediate rotational and translational stability. The implants are fenestrated — they contain openings that allow bone to grow through over time for solid fusion.
6. Fluoroscopic views confirm correct implant depth, angle, and position within the sacrum.
7. The incision is closed with sutures or staples.

Approach B — Posterior SI Joint Fusion

1. You are positioned face-down on the operating table.
2. A small posterior incision is made near the posterior superior iliac spine (PSIS).
3. Under fluoroscopic guidance, a trajectory is established from the posterior ilium directed across the SI joint toward the sacral ala and body.
4. One or more implants or cannulated screws are placed along this posterior-to-anterior trajectory, crossing and compressing the SI joint.
5. If this is performed as an extension of an existing lumbar fusion, the implant or screw is connected to or aligned with the lumbar construct.
6. Fluoroscopic views confirm implant position. The incision is closed.

Risks of Surgery

General Surgical Risks

• Infection — superficial or deep wound, epidural abscess, meningitis
• Bleeding or blood transfusion
• Blood clots (DVT or pulmonary embolism)
• Stroke
• Heart attack
• Paralysis
• Death
• Adverse anesthesia reaction
• Pneumonia or urinary tract infection
• Vascular or abdominal/pelvic injury
• Corneal abrasion or blindness
• Ulnar nerve, median nerve, or brachial plexus injury from positioning
• Additional surgery for any noted or unforeseen complications

Procedure-Specific Risks

• Implant malposition requiring revision
• L5 nerve root injury — from posterolateral approach corridor
• Superior gluteal nerve or artery injury
• S1 or S2 nerve injury — from posterior approach corridor
• Weakness in the leg including foot drop
• Nerve root injury — sensory changes, weakness, or paralysis (temporary or permanent)
• Persistent or unchanged SI joint pain
• Incomplete or failed fusion requiring additional surgery
• Sacral, pelvic, or iliac fracture
• Unforeseen metal allergy
• Implant prominence or pain — may require implant removal
• Loss of bowel, bladder, or sexual function
• Symptoms may be unchanged, worse, different, or new after surgery

Your Hospital Stay

Most patients go home the same day. An overnight stay is occasionally needed for pain management or observation.

Recovery at Home

Activity Timeline

• Weeks 1–2: Toe-touch or partial weight-bearing as directed. No lifting more than 10 lbs.
• Weeks 2–4: Weight-bearing advanced as tolerated. Short walks with assistive device, increasing distance daily.
• Weeks 4–6: Transition to full weight-bearing. Most patients are off assistive devices by 4–6 weeks.
• After 6 Weeks: Activity advanced at your follow-up visit based on progress and imaging.

Return to Work — Typical Timelines

All timelines are estimates. Your surgeon will provide formal work release at follow-up based on your progress.

Wound Care

• Keep the incision clean and dry for the first 48–72 hours after discharge.
• You may shower after 48 hours — allow water to run gently over the area. Do not scrub.
• Do not submerge in a bathtub, pool, or hot tub until cleared by your surgeon (typically 4–6 weeks).
• Steri-strips should fall off on their own over 7–10 days. Do not remove them.
• Dissolvable sutures do not need removal. External sutures or staples are removed at your 2-week visit.
• Monitor for signs of infection and call our office promptly if you have concerns.

Medications at Discharge

• Opioid pain medication — Use only as needed for pain not controlled by other measures. Do not drive, operate machinery, or consume alcohol while taking opioids. Short-term use only (1–2 weeks typical).
• Muscle relaxer — Helps reduce painful muscle spasm. May cause drowsiness.
• Stool softener (docusate) — Take while using opioids to prevent constipation. Drink 6–8 glasses of water daily.
• Acetaminophen (Tylenol) — Do not exceed 3,000 mg/day. Do not take additional Tylenol-containing products concurrently.

Opioids are for short-term use only — typically 1–2 weeks. Taper as pain allows. Do not request early refills. Dispose of unused medication safely at a pharmacy take-back program.

Follow-Up Schedule

Warning Signs

For urgent concerns outside of office hours, call (405) 748-3300 — our answering service is available 24 hours a day, 7 days a week.