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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.

A stethoscope on a clinical desk

Indicative pricing

What private SI joint fusion costs in London.

Indicative ranges across UK units.

In short

£22,000–£32,000, often home the same day.

Procedure Indicative range
Initial complex-spine consultation £280–£450
Image-guided SI joint diagnostic block (per side) £450–£850
Cooled SI lateral-branch RFA £3,500–£5,500
MIS SI joint fusion, iFuse triangular titanium (unilateral) £22,000–£32,000
MIS SI joint fusion, staged bilateral £35,000–£48,000
Second-opinion review of imaging and blocks £250–£450

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.

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.

  • 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.

  • 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.

  • 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.

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).

  • Post-partum SI dysfunction

    Persistent posterior pelvic pain after delivery, with a positive Fortin finger sign and three or more provocative tests.

  • Degenerative sacroiliitis

    CT-confirmed joint degeneration with concordant pain, in a patient over 50 who has failed physio and steroid injection.

  • 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.

  • 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.

  • Failed conservative pathway

    6 months of physio, SI belt and image-guided intra-articular steroid without sustained benefit, plus positive dual blocks.

  • Failed lateral-branch RFA

    RFA gave temporary relief that has now worn off, or gave no relief despite a well-placed lesion pattern.

  • Not for you: axial spondyloarthropathy

    Inflammatory sacroiliitis in AS is a rheumatological disease, not a surgical one. Biologics, not implants.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • Physiotherapy and SI belt

    Lumbopelvic stability, gluteal reactivation and a trochanteric SI belt. First line, and continues after any interventional step.

  • Second-opinion review

    A specialist review of your MRI, CT, blocks and RFA history. Sometimes the answer is a different diagnosis, not another needle.

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.

  • 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%.

  • 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.

  • 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.

  • Transient buttock numbness

    A small patch of numbness over the incision from cluneal-nerve stretch. Usually settles over weeks to a few months.

  • 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.

  • Physio from week two

    A structured lumbopelvic stability programme from week two. This is not optional, and the outcome depends on doing it.

  • 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.

  • 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.

  • 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 London complex-spine surgeon reviewing SI joint imaging and block records

A quiet reminder

Spinal language is precise and can read coldly - ask your care team to explain anything that is unclear.

Ask your care team to explain anything that is unclear.

  1. 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.

  2. 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.

  3. 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.

  4. 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

BupaAXA HealthVitalityAvivaWPACignaHealixBupaAXA HealthVitalityAvivaWPACignaHealixBupaAXA HealthVitalityAvivaWPACignaHealix

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.

Frequently asked

Everything we get asked about SI joint fusion.

Quick answers on diagnosis, the ladder before surgery, the operation itself, outcomes and cost.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

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