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Sacroiliac (SI) Fusion

If you suffer from sacroiliitis that is not responding to treatment, this highly advanced and minimally invasive procedure may be an option for you.  SI Fusion is a proven treatment option for low back pain caused by a painful or hyper-mobile sacroiliac joint.  It is a one time treatment that stabilizes the SI joint and eliminates pain right at the source.

What is an SI Fusion?

Sacroiliac fusion, or SI Fusion, is a brand new procedure that combines the minimally invasive nature of pain management with the precision of orthopedic surgery.  Previously, the only way to fuse an SI joint was to use a drill and insert 3 large rods through the hip bone and into the sacrum.

While effective, the procedure was extremely invasive, caused significant bleeding and lot of post-operative pain.  Fortunately, there is a new cutting-edge technique for performing this procedure that can be completed through button hole size incision that reduces the recovery period to a fraction of the time.

The Ainsworth Institute is proud to partner with PainTEQ to offer the LinQ – a minimally invasive alternative to SI Fusion that provides the same level of fusion to the joint as older platforms but through a single incision!


Sacroilitis is a relatively common cause for low back pain.  It is commonly confused with low back pain and goes un-diagnosed in a surprisingly large amount of instances.  Sacroiliitis accounts for as much 20% of the total causes low back pain in the United States. [1][2]  SI joint pain can occur on its own but is more common after trauma, pregnancy or lumbar fusion surgery.  Some of the signs of sacroiliitis include:

Low back pain that radiates into the buttocks
Pain that radiates into the posterior part of the thigh
Pain in the groin
Pain that gets worse when you cross your legs
Pain that gets better when you stand up
Tenderness to palpation over the SI Joint

Learn More About Sacroiliitis and How it Causes Pain

How Does it Work?

The SI joint is meant to move between 2-4mm in healthy individuals.  When it starts moving more than that, it causes inflammation which in turn causes pain.  Excessive movement occurs when the joint destabilizes – this can occur with trauma or after surgery.  If your lumbar spine was fused down to your sacrum, the SI joint will start to loosen up over matter of time – it’s unavoidable.

The rationale for fusing the SI joint is obvious – if the joint moving too much causes pain, then let’s stop it from moving.  But therein lies the dilemma – the joint is meant to move a slight amount, preventing the joint from moving at all will cause the opposite SI joint to destabilize as will as putting excessive stress on the L5/S1 disc.  The solution is to decrease the excessive movement, but preserve the slight amount of movement the joint is meant to have.  That is precisely what the LinQ does. 

A small dowel with bone matrix inside is inserted into the middle part of the joint.  Over a the next few weeks, that bone matrix will grow into either side of the SI joint causing it to tighten up and reduce the movement that was causing pain in the first place.  Think of it like a seesaw that rattles and moves from side to side whenever it moves up and down – the solution isn’t just fuse the seesaw.  That would defeat the purpose of it.  Instead, you would tighten down the bolt in the middle at the fulcrum.  The seesaw can still go up and down, but now it doesn’t rattle and only moves in the direction it is supposed to move.

Is LinQ as Effective as Doing a "Lateral" Fusion?

Yes!  In a study funded by SI-Bone in 2015, there was no difference found between fusing the SI joint through a side approach versus an approach from the back.  Both were found to be equally as effective in reducing movement in the joint.  This is great news for patients since the LinQ procedure is a far less invasive technique and we know for a fact through this study that we are not sacrificing any quality in the process.


Anatomy of the Pelvic Sacroiliitis Sacroiliac Joint PainThe sacroiliac joint is a highly complex joint and is most often classified as a “diarthrodial” joint. It has several components to its structure:

  • fibrous joint capsule with thick synovial fluid
  • cartilaginous surfaces
  • ligamentous connections.

Unlike most joints, the SIJ is not very mobile – it serves more to provide stability and weight-bearing capability. While there is some small amount of movement in the SIJ, there has not been a relationship seen between the degree of movement of the joint and pain.
The joint is supported by a group of muscles that attach to the joint itself and aid with walking, sitting, standing, and as well as providing support and stability. These muscles include the gluteus maximus and medius, biceps femoris, piriformis, latissimus dorsi and erector spinae.[1] The SIJ is designed for stability and weight-bearing.
The nerve supply to the SIJ is equally as complex and has been the subject of some debate amongst physicians.

  • Dorsal Aspect: innervated by the S1-S3 dorsal rami.[4] Some studies suggest innervation from the L5 nerve, and a recent cadaver study found contribution from the S4 nerve in 59% of joints.[5]
  • Ventral Aspect: innervated by the L4-S2 ventral rami, while others include levels as high as L2.[6][7]

Most physicians will agree that pain from the SIJ can occur from within the joint as well as immediately outside it due to pain receptors being located throughout the joint capsule as well as in the adjacent muscles and ligaments. Pain receptors within the joint capsule are mostly found in the proximal and middle thirds of the joint – this is where most procedures targeting pain from the SIJ will be performed.

What Are the Benefits?

The SI joint is meant to move between 2-4mm in healthy individuals.  When it starts moving more than that, it causes pain.  Movement occurs when the joint destabilizes – this can occur with trauma or after surgery.  If your lumbar spine was fused down to your sacrum, the SI joint will start to loosen up over matter of time – it’s unavoidable.

Steroid injections into the SI Joint are effective at reducing pain but will inevitably wear off in a matter of weeks.  They can be repeated up to 3 times over a 12 month span but what happens if you need more than 3?  Or what do you do it you do not want to get an injection with steroids every 3 months for the rest of your life?

One alternative is a radiofrequency ablation (RFA) – these are a safe and effective way to block the pain signals from a painful SI Joint for over a year.  The obvious downside is that this will need to be repeated as well.  Unfortunately, if the pain is coming from the anterior (front) aspect of the SI joint, the RFA will be ineffective.  Also, if the joint is hypermobile, the RFA will wear off quicker meaning the procedure will need to be repeated more often.

This is where an SI Fusion comes into play – it is a one time procedure that fixes the problem instead of covering it up.  Keeping in mind that the SI joint is supposed to move a little bit, the LinQ procedure reduces the movement of an unstable SI joint back down to the minimal amount of 2-4mm by tightening the joint and making it more difficult for it to move when you move.  The beauty of the LinQ procedure is it preserves that slight amount of movement that a normal SI joint was meant to have rather than completely fusing it, altogether, which would cause damage to the opposite joint by making it destabilize in turn. 

How Many Treatments Will I Need?

Just one!

When Will I Feel Better?

There is some mild post operative pain that typically passes with a day or 2.  You should start to feel the effects of the fusion within 7-10 days.

Is an SI Fusion Right for Me?

The first and most important step is confirming that the sacroiliac joint is actually the cause.  The gold standard for diagnosing sacroiliac joint pain is a sacroiliac joint injection. This procedure is both diagnostic and therapeutic meaning it can not only diagnose SI Joint pain but potentially treat it.  In many cases, the pain will come back in a few weeks in which case the injection would need to be repeated over and over again.  If the pain comes back, then an SI fusion would likely be the next step.

Procedure - Patient Details

Your physician will first select the appropriate medication to be used in the infusion depending on your diagnosis and the type of pain you are experiencing. Then the office staff will weigh you to determine the proper amount of medication needed and mix it with saline in an IV bag. Next your physician will place an IV catheter in your arm or hand; this is no different than any other way an IV would be placed. And lastly, the medication is infused, taking 30 minutes to several hours. It’s that simple. During the infusion process, you will be placed on a monitor and your vitals will closely observed for the duration of the procedure. The key to intravenous infusion therapy is not how much medication goes in, rather how much over how long.


The most obvious advantage that an SI Fusion has over other treatment for sacroiliitis is the fact that it is a one time procedure as opposed to injections and ablations that need to be periodically repeatedly.  The most well known SI Fusion platform is called iFuse from a company name SI Bone.  While very effective, the procedure is unnecessarily invasive – in order to insert the dowels to fuse the joint, the doctor will need to drill into the bone.  This causes a significant amount bleeding unto itself.  Compound that with the fact that there are THREE dowels that need to be placed and now you have bone being drilled in 3 different spots which creates for even more bleeding and an even longer recovery time.

The LinQ procedure is able to produce the same level of fusion at the joint without any drilling and only one fusion point.  The benefits of the LinQ over iFuse are obvious.

Risk Factors

The risk profile for the LinQ procedure is relatively low.  It is considered a minor surgery so it carries the same risks as any such procedure.  The a small risk of bleeding and infection – the later is effectively lowered by the fact that your doctor will likely give you antibiotics at the beginning of the procedure as well as give you a course of them to take for about a week afterwards.  There will be some mild postoperative pain after the procedure that typically passes within a day or 2.

Evidence of Performance

Sacroiliac joint fusions are nothing new – this procedure has been around for decades. What has changed over the years has been the technique and the steady decrease in the level of invasiveness. Originally, the only way to fuse an SI joint was a big, open surgery whereby large metal plate were secure down to the sacrum and the ilium using bone screws. While effective, the recovery time was extensive and the pain from the procedure itself often outweighed the pain from the sacroiliitis, itself. Over time, techniques emerged to be able to fuse the joint through small incisions that utilized small rods or dowel that would be inserted laterally through the ilium and into the sacrum.[3] These procedure were shown to provide statistically significant reductions in pain and improvements in function.[4] To date there are more than 80 publication on SI fusion with Level-I data to support it.

The Ainsworth Institute is Here to Help

The doctors at the Ainsworth Institute of Pain Management specialize in managing and treating sacroiliac joint pain. Dramatic improvements in pain and quality of life are attainable with the right treatment regimen. Schedule an appointment today with one of our board certified pain management experts to discuss what options for treatment may best suit your needs.


[1] Benzon, Honorio. Essentials of Pain Medicine. Philadelphia: Saunders Elsevier, 2011. Print
[2] Schwarzer AC, Aprill CN, Bogduk N. The sacroiliac joint in chronic low back pain. Spine 1995; 20:31-37.
[3] Ledonio CG, Polly DW, Swiontkowski MF. Minimally invasive versus open sacroiliac joint fusion: are they similarly safe and effective?. Clin Orthop Relat Res. 2014;472(6):1831-8.
[4] Dengler J, Kools D, Pflugmacher R, Gasbarrini A, Prestamburgo D, Gaetani P, Cher D, Van Eeckhoven E, Annertz M, Sturesson B. Randomized Trial of Sacroiliac Joint Arthrodesis Compared with Conservative Management for Chronic Low Back Pain Attributed to the Sacroiliac Joint. J Bone Joint Surg Am. 2019 Mar 6;101(5):400-411. doi: 10.2106/JBJS.18.00022. PMID: 30845034; PMCID: PMC6467578.