Sacroiliac Joint (SI Joint) Anatomy

The sacroiliac joint (SI joint) is located in the pelvis; it links the iliac bones (pelvis) to the sacrum (lowest part of the spine above the tailbone). It is an essential component for shock absorption to prevent impact forces from reaching the spine. Many problems can cause sacroiliac joint pain, and, fortunately, various types of SI joint treatment are available.

Do you have SI Joint Problems?

The SI joint is a significant cause of low back pain. Clinical publications have identified the SI joint as a pain generator in 15-30% of chronic low back pain patients. 1-4 In addition, the SI joint is a pain generator in up to 43% of patients with continued or new onset low back pain after a lumbar fusion. 5

Like any other joint in the body, the SI joint can be injured and/or become degenerative. When this happens, people can feel pain in their buttocks and sometimes in the low back and legs. This is especially true while lifting, running, walking or even sleeping on the involved side. According to scientific data, it’s common for pain from the SI joint to feel like disc or low back pain. For this reason, SI joint disorders should always be considered in the diagnosis of such pain.

anatomy of pelvis

A sudden and traumatic injury, an existing condition (differences in leg length, twisted pelvis, or muscle imbalance), or inflammatory joint disease can cause sacroiliac pain. Hormonal changes during pregnancy can as well.

Do you experience one or more of the symptoms listed below?

  • Low back pain
  • Sensation of low extremity: pain, numbness, tingling, weakness
  • Pelvis/buttock pain
  • Hip/groin pain
  • Pain radiating down one or both legs
  • Feeling of leg instability (buckling, giving way)
  • Disturbed sleep patterns
  • Disturbed sitting patterns (unable to sit for long periods, sitting on one side)
  • Pain going from sitting to standing
  • Limited range of motion
  • Limping
  • Fever
  • Eye inflammation

Making a Diagnosis

A variety of tests performed during physical examination may help reveal the SI joint as the cause of your symptoms. Sometimes, X-rays, CT-scan or MRI may be helpful in the diagnosis of SI joint-related problems.

The most relied upon method to accurately determine whether the SI joint is the cause of your low back pain symptoms is to inject the SI joint with a local anesthetic. The injection will be delivered under either X-ray or CT guidance to verify accurate placement of the needle in the SI joint. If your symptoms are decreased by at least 50%, it can be concluded that the SI joint is either the source of or a major contributor to your low back pain. If the level of pain does not change after SI joint injection, it is less likely that the SI joint is the cause of your low back pain.

Treatment Options

Once the SI joint is confirmed as the cause of your symptoms, treatment can begin. Some patients respond to physical therapy, use of oral medications, or injection therapy. These treatments are often performed repetitively, and frequently symptom improvement using these therapies is temporary. At this point, you and your surgeon may consider other options, including minimally invasive surgery.

SI Joint Fusion with the iFuse Implant System®

The iFuse Implant System is designed to provide stabilization and fusion for certain SI joint disorders. This is accomplished by inserting triangular shaped titanium implants across the sacroiliac joint to maximize postsurgical stability and weight bearing capacity. The procedure is done through a small incision (about 2-3 centimeters long) and takes about an hour. Multiple published studies on iFuse have documented procedure safety and effectiveness. 6

doctor with patient

Often performed when non-surgical treatment options fail, SI joint fusion may involve general or spinal anesthesia. The surgeon uses fluoroscopy to obtain live images, so they can properly place the iFuse Implant System. Real-time moving images help the surgeon see internal biological structures and where the surgical instruments are. During the procedure, no bone grafting is needed, and there is reduced trauma on soft tissues and tendons compared to traditional methods.

Patients are discharged based on their progress and health status following the spine surgery. It’s important to follow a doctor’s advice about when to resume daily activities, bear weight on the site, and return to work.

In addition to being minimally invasive, the procedure offers the benefits of a triangular implant, which minimizes rotation and micromotion that can cause more sacroiliac joint pain. Bone growth onto and into the implant is enabled thanks to a porous titanium surface, while the device is engineered to fuse and stabilize the joint.

Many patients avoid surgery, with treatments such as anti-inflammatory medications, physical therapy, and corticosteroid injections. The new SI joint fusion is not only minimally invasive; it also results in rapid and sustained pain relief. In studies, 82% of patients indicated they were satisfied with the short- and long-term results. 7

References:

  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 Patients Having Undergone Lumbar Fusion. Pain Med. 2011;12:732-9.
  6. Polly, D.W.* et al., Neurosurgery. 2015. A list of additional published studies is available at www.si-bone.com/results
  7. Rudolf* et al., Sacroiliac joint arthrodesis-MIS technique with titanium implants: report of the first 50 patients and outcomes. Open Orthopaedics Journal. 2012,6:495-502. * Paid consultant of, conducts clinical research for, and has an ownership interest in SI-BONE, Inc.

* Dr. Polly is an investigator on a clinical research study sponsored by SI-BONE. He has no financial interest in SI-BONE. Research was funded by SI-BONE, Inc.

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