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Sacro-Illiac (SI) Joint Fusion

Sacro-Illiac (SI) Joint Fusion

The sacroiliac joint, or SI joint, is a large L-shaped synovial joint in the pelvis that connects the sacrum and the ilium of the pelvis. This joint is a strong, weight bearing joint on both sides of the pelvis. These joints are supposed to move together as single unit. Just like other joints in the body, this joint has strong internal and external ligaments. The SI joints’ function is additional for shock absorption for the spine. As we age, the joint’s stability can change as ligaments become loose and the joint surfaces lose their original orientation.


Sacroiliac joint pain is often from dysfunction from one of the two joints. When one joint does not move properly pain may be felt as one-sided low back pain or midline “tailbone” pain. The joint can move too much (hypermobility) or too little (hypomobility) and can feel “locked-up”. Pain can be dull or very sharp. When SI joint dysfunction is severe, this joint can refer pain to the hip, groin, buttocks, and even down the back of the thigh. Pain may be worse with movements that stress that joint, such as standing up from a seated position, walking up an incline, elliptical exercise, and prolonged sitting or walking. This pain can be similar to pain experienced with degenerative hip disease, hip bursitis, lumbar disc herniation, or lumbar radiculitis. This joint can also become inflamed called sacroiliitis. The SI joint has many relationships with large and small muscles, all of which can be affected. These muscles can spasm from joint dysfunction or inflammation.

Sacroiliac Joint Fusion

Sacroiliac (SI) joint fusion is a technique used to stabilize the sacroiliac joint. This is generally used to treat back or leg pain caused by SI joint dysfunction. Within the past few years, there has been resurgence in the recognition of the SI joint as a potential source of low back pain as treatment options for SI joint dysfunction have advanced. One study found that up to 25% of patients presenting to a spine clinic had significant pain from the hip or SI joint1. The majority of patients can be treated non-operatively through anti-inflammatory medications, physical therapy, or SI joint injections. However, some patients will require surgical treatment when conservative therapies have failed to improve symptoms.

Numerous techniques exist for the surgical treatment of sacroiliac joint dysfunction. The main goal is to stabilize the joint by using implants and sometimes instrumentation.

One surgical technique our spine surgeon’s use is the iFuse system. In the iFuse system, triangular shaped titanium rods are placed across the sacroiliac joint. These rods provide initial stabilization and can offer significant improvement in pain. The iFuse procedure relies upon an implant surface technology to encourage bone growth into these devices. Both the triangular shape and the implant coating are designed to prevent rotation and motion of the SI joint. This will hopefully give long-term stability to the joint.

Another technique used is the Zyga SImmetry system. This affords stabilization across the SI joint from two large compression screws. This technique allows a device to be placed directly into the SI joint to remove soft tissue and prepare the bone for fusion. Once the SI joint has been prepared, bone graft can be placed within the joint. Two screws are placed across the joint for stability with the long-term goal of solid fusion of the SI joint. Both of these technologies are minimally invasive.

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