Complex spine · London
Sacroiliac joint fusion, by a complex-spine surgeon.
Day-case iFuse minimally invasive SI joint fusion under NICE IPG578, done by a consultant with a dedicated SI practice. Only offered after dual diagnostic blocks, image-guided steroid and lateral-branch RFA have honestly been tried.
Why patients choose us
- 01
A named complex-spine surgeon, high SI volume
Not a general spinal list. A consultant with a dedicated SI joint practice, in a unit set up for navigation and intra-operative neuromonitoring.
- 02
The full pain-ladder, not just the operation
Physio, image-guided intra-articular blocks and lateral-branch RFA come first. Fusion is offered only when the ladder is genuinely exhausted.
- 03
Independent, and free
We are paid by no clinic, so the recommendation is impartial and costs you nothing.
Indicative pricing
What private SI joint fusion costs in London.
Indicative ranges across our partner units. Send imaging and block history and we quote firm figures across two or three options.
In short
A unilateral MIS SI fusion in our London network: £22,000–£32,000, often home the same day.
| Procedure | Indicative range | Typical duration | Turnaround |
|---|---|---|---|
| Initial complex-spine consultation | £280–£450 | 45–60 min | Same visit |
| Image-guided SI joint diagnostic block (per side) | £450–£850 | 20–30 min | Same visit |
| Cooled SI lateral-branch RFA | £3,500–£5,500 | 60–90 min | Same visit |
| MIS SI joint fusion, iFuse triangular titanium (unilateral) | £22,000–£32,000 | 45–60 min | Same visit |
| MIS SI joint fusion, staged bilateral | £35,000–£48,000 | 2 sittings | 6–12 wks apart |
| Second-opinion review of imaging and blocks | £250–£450 | 30 min | 48 hours |
Prices vary by unit (King's Private Spine, HCA Wellington Complex Spine, London Bridge Spine, RNOH Private, Nuffield Parkside Spine), by surgeon, and by implant system. NHS availability under NICE IPG578 is patchy. We come back with a firm quote within one working day.
The problem
The right diagnosis, the right ladder, the right implant.
Cohen estimates the SI joint accounts for around 25% of chronic low back pain, and it is systematically missed on lumbar MRI. Fusion done on the wrong patient is a bad operation. We stop that happening.
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Is it actually your SI joint?
Fortin finger sign, three or more provocative tests, and two positive image-guided intra-articular blocks. Nothing else confirms the diagnosis.
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Have you exhausted the ladder?
Six months of physio, an SI belt, image-guided steroid and cooled lateral-branch RFA come first. Fusion is offered only when the ladder is done.
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Want it done in a specialist unit?
A named complex-spine surgeon, navigation, intra-operative neuromonitoring of S1 and S2, and a physio pathway ready from week two.
The journey
From referral to fusion - what happens, in order.
One team from first message to physio at week two - including the diagnostic blocks that confirm the joint before we ever talk about implants.
Phase 1 · Before your procedure
Concierge, off-stage for you
Phase 2 · On the day
Day case or one-night stay
Phase 3 · After
Physio and follow-up
- 01
Before
You send us imaging and pain history
A short, confidential form. MRI lumbar spine and pelvis, any prior blocks or RFA, provocative test findings, and how the pain limits your day.
- 02
Before
We come back with a recommendation
Within one working day: whether dual diagnostic blocks are the next step, whether RFA is worth trying, or whether MIS SI fusion is on the table. Indicative price. An honest read either way.
- 03
Before
Dual diagnostic blocks
Two image-guided intra-articular local anaesthetic blocks, at least a week apart. Both must give at least 75% pain relief for the expected duration to confirm the SI joint per Laslett and NASS criteria.
- 04
On the day
Admission and marking
Admission, consent, and a chat with the surgeon and anaesthetist. GA with intra-operative neuromonitoring of S1 and S2 nerve roots.
- 05
On the day
The MIS SI fusion itself
45 to 60 minutes. A 3 cm lateral incision, fluoroscopic or CT navigation, and three triangular titanium implants placed across the joint on a transiliac trajectory.
- 06
On the day
Day case or one-night stay
Weight-bearing as tolerated with crutches from day one. Home the same day for most, one night in for bilateral or complex cases.
- 07
After
Physio and review
Guided physio from week two. Wound review at two weeks, surgeon review at six weeks and three months, imaging at one year. Full return to sport usually 4 to 6 months.
Typical end-to-end: 6–8 weeks from enquiry through blocks to fusion. Physio: from week two. Full recovery: 4–6 months.
When it helps
When MIS SI fusion is the right step - and when it is not.
The patients we see most, plus the presentations that mean a different pathway (rheumatology, hip, lumbar spine, or urgent MRI).
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Post-partum SI dysfunction
Persistent posterior pelvic pain after delivery, with a positive Fortin finger sign and three or more provocative tests.
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Degenerative sacroiliitis
CT-confirmed joint degeneration with concordant pain, in a patient over 50 who has failed physio and steroid injection.
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Adjacent-segment SI pain after lumbar fusion
The classic story: L4-S1 fusion, then new posterior buttock pain over the PSIS. Reported in up to 40% of long-construct fusions.
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Post-traumatic SI joint pain
A fall on the buttock, a road-traffic injury or a childbirth injury with persistent unilateral pain and a positive block.
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Failed conservative pathway
6 months of physio, SI belt and image-guided intra-articular steroid without sustained benefit, plus positive dual blocks.
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Failed lateral-branch RFA
RFA gave temporary relief that has now worn off, or gave no relief despite a well-placed lesion pattern.
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Not for you: axial spondyloarthropathy
Inflammatory sacroiliitis in AS is a rheumatological disease, not a surgical one. Biologics, not implants.
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Red flag: bilateral radiculopathy, saddle anaesthesia
True neurological deficit, cauda equina symptoms or unexplained weight loss needs urgent MRI and referral, not a fusion consultation.
Treatment options
SI joint pain is a ladder, not a single procedure.
What each rung on the ladder actually involves, from physio and belt through image-guided injection and RFA to MIS fusion.
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iFuse triangular titanium (SI-BONE)
Three porous titanium implants placed transiliac through a 3 cm incision. The INSITE and SIFI trials showed superiority to non-surgical care at 24 months. NICE IPG578 supportive.
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Allograft dowel systems (SIFix, TriFix, SIROS)
Cortical-bone dowels packed into the joint on a posterior or lateral trajectory. Newer devices, promising early data, less long-term evidence than iFuse.
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Posterior interpositional (SILEX, LinkSI)
A single implant placed posteriorly, into the joint from behind. Shorter procedure, less soft-tissue dissection, chosen in selected slim patients.
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Image-guided intra-articular steroid
Ultrasound or fluoroscopic injection of local anaesthetic and steroid into the joint. Diagnostic and therapeutic, with 60 to 80% temporary benefit.
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Cooled or multi-lesion lateral-branch RFA
Cooled RF (Simplicity, Nimbus) creates larger lesions of the sacral lateral branches. 6 to 18 months of benefit, repeatable. NICE IPG578.
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Diagnostic dual blocks
Two image-guided intra-articular local anaesthetic blocks with 75% or greater pain relief for at least three hours per block. NICE and NASS dual-confirmation standard.
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Physiotherapy and SI belt
Lumbopelvic stability, gluteal reactivation and a trochanteric SI belt. First line, and continues after any interventional step.
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Second-opinion review
A specialist review of your MRI, CT, blocks and RFA history. Sometimes the answer is a different diagnosis, not another needle.
Our vetted London network
A small panel of complex-spine surgeons, we picked them.
Consultant spinal surgeons with dedicated SI joint practices at King's Private Spine, HCA Wellington, London Bridge Spine, RNOH Private and Nuffield Parkside. Not listed publicly - introductions are made privately, once we understand your case.
Selection criteria
How we choose every surgeon in our network.
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Consultant spinal surgeons with dedicated SI joint practices, not occasional cases
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Intra-operative neuromonitoring of S1 and S2 nerve roots on every fusion
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Fluoroscopic or CT navigation to avoid implant malposition
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Interventional pain team on site for blocks and RFA before surgery is offered
Safety and recovery
What to expect afterwards - honestly.
Outcomes at 24 months are strong (60 to 80% substantial pain reduction, major ODI improvement in the SIFI cohort), but selection and physio matter as much as the implants.
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General anaesthetic with neuromonitoring
GA with continuous monitoring of S1 and S2 nerve-root function. Navigation and neuromonitoring together have brought the early-series nerve-injury rate down to well under 2%.
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Implant malposition and nerve injury
S1 nerve-root irritation or true injury was reported in 1 to 2% of early iFuse series. Modern navigation has reduced this substantially, but it remains the key intra-operative risk.
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Wound problems
Superficial wound issues in around 2 to 4%. Higher in smokers and in patients with a raised BMI. Discussed and mitigated before you consent.
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Transient buttock numbness
A small patch of numbness over the incision from cluneal-nerve stretch. Usually settles over weeks to a few months.
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Weight-bearing as tolerated from day one
Crutches for two to four weeks. Driving from three weeks for most. Desk work at two weeks. Manual work and sport at 3 to 6 months.
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Physio from week two
A structured lumbopelvic stability programme from week two. This is not optional, and the outcome depends on doing it.
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Residual back pain is common
The SI joint is often one of several pain generators. Residual lower back pain from concurrent lumbar disease is quoted honestly before surgery.
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Revision at 5 years around 5 to 10%
Registry data suggests a 5 to 10% revision rate at five years, mainly for implant loosening or ongoing pain from an adjacent generator.
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Red flags after discharge
Fever, spreading wound redness, new leg weakness, saddle numbness, bladder or bowel change - call the unit or go to A&E the same day.
Reading your consultation notes
Your SI assessment in four parts. Read the last one first.
Whichever surgeon sees you, the notes keep to the same shape. If a section is missing, ask for it.
A quiet reminder
Spinal language is precise and can read coldly - we translate it for you.
If you would like us to talk you through the notes before your review, just ask.
- 01 History
Fortin finger sign and provocative pattern
Where you point (posterior over the PSIS, radiating into buttock and posterior thigh) and how many of the five provocative tests were positive.
- 02 Imaging
MRI to exclude, CT for congruency
MRI lumbar spine and pelvis to rule out disc, facet or hip disease. CT to assess joint congruency and safe implant corridors.
- 03 Blocks
Dual diagnostic confirmation
Two image-guided intra-articular local anaesthetic blocks, with the percentage and duration of pain relief for each. This is the gate to any surgical offer.
- 04 Plan
Ladder step, indication and outcome quote
Read this first: whether the next step is physio, injection, RFA or fusion; the honest quoted percentage of substantial pain reduction; and what residual pain to expect.
Recognised by major UK insurers
Cover for MIS SI joint fusion under NICE IPG578 varies by insurer. Bupa, AXA and Vitality generally fund with prior authorisation and evidence of dual blocks. We confirm cover before booking.
Frequently asked
Everything we get asked about SI joint fusion.
Quick answers on diagnosis, the ladder before surgery, the operation itself, outcomes and cost.
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How common is SI joint pain as a cause of low back pain?
Cohen and colleagues estimate the sacroiliac joint accounts for around 25% of chronic low back pain, particularly pain that sits over the posterior superior iliac spine and radiates into the buttock and posterior thigh rather than down the leg. It is systematically under-diagnosed because it is not a lumbar spine problem and does not show on a standard lumbar MRI.
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How is SI joint pain actually diagnosed?
Clinically with the Fortin finger sign and at least three of five provocative tests (sacral thrust, distraction, compression, Gaenslen, thigh thrust) per Laslett criteria. Confirmed with two image-guided intra-articular local anaesthetic blocks, each giving at least 75% pain relief for the expected duration. NICE and NASS require this dual-block confirmation before considering fusion.
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What is the treatment ladder before surgery?
Physiotherapy for lumbopelvic stability, an SI belt, then image-guided intra-articular steroid (60 to 80% temporary benefit), then cooled or multi-lesion lateral-branch RFA (6 to 18 months benefit, repeatable, NICE IPG578). MIS SI fusion is offered when six months of that ladder has failed and dual blocks are positive.
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What does MIS SI fusion actually involve?
Under GA with neuromonitoring, a 3 cm lateral incision. Three triangular titanium implants (iFuse) are placed across the joint on a transiliac trajectory under fluoroscopic or CT navigation. The procedure takes 45 to 60 minutes. Most patients go home the same day and are weight-bearing on crutches from day one.
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How well does it work?
The INSITE and SIFI randomised trials showed iFuse superior to non-surgical care at 24 months. Around 60 to 80% of properly selected patients report substantial pain reduction at two years, with major improvements in Oswestry Disability Index. Selection is everything: patients with positive dual blocks and a clean pain map do best. NICE IPG578 supports the procedure.
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How much does private SI joint fusion cost in the UK?
Roughly £22,000 to £32,000 for a unilateral MIS SI fusion, and £35,000 to £48,000 for staged bilateral. Diagnostic blocks are £450 to £850 per side and cooled lateral-branch RFA is £3,500 to £5,500. NHS availability under NICE IPG578 is patchy and heavily gated, which is why most patients in England pay privately or go through PMI.
Ready to talk?
Send us your MRI and block history. We come back within a working day.
No pushy sales, no clinic on commission. An honest read on whether the next step is physio, an injection, RFA, MIS SI fusion, or nothing at all.
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