The sacroiliac (SI) joint connects the sacrum (base of the spine) to the pelvic bones (ilium), transferring weight and forces between the upper body and the legs. When this joint becomes a source of chronic pain and instability, SI joint fusion may be recommended to stabilize the joint by permanently joining the bones together. While the goal is to alleviate debilitating pain and improve function, the procedure is not without potential negative outcomes. This article focuses exclusively on the drawbacks and complications associated with this surgical intervention.
Immediate Post-Operative Complications
SI joint fusion involves standard acute risks common to most orthopedic surgeries. One common concern is a surgical site infection, which can be superficial or deep (osteomyelitis). Infections delay healing, cause significant pain, and often require further medical or surgical intervention.
The procedure also carries the risk of excessive bleeding (hemorrhage) during or immediately after the operation. Another serious complication is damage to nearby neurological structures, particularly the sciatic nerve, which passes close to the SI joint. Nerve injury can result in new or worsened neurological deficits, such as numbness, tingling, or weakness in the leg or foot. Patients are also exposed to the general risks associated with anesthesia.
Hardware Failure and Implant Issues
A significant downside of SI joint fusion involves potential issues with the implants—such as screws or triangular titanium devices—used for stabilization. The implants are intended to hold the joint rigid until the bones fuse together, but they can fail mechanically, often necessitating additional surgery.
Implant Migration
Implant migration occurs when the hardware shifts from its initial placement, potentially impinging on sensitive structures like the sacral nerves. This can cause severe new pain or loss of bowel and bladder control.
Hardware Loosening and Fracture
Hardware loosening is a common problem where the implant becomes unstable over time, often before the joint has fully fused, leading to a return of pain and instability. The forces applied to the joint can also cause the hardware to fracture or break. These hardware-related complications frequently lead to localized pain around the implant site and require revision surgery.
Persistent or Recurrent Pain
The primary objective of SI joint fusion is pain relief, but the procedure may fail to achieve this goal, resulting in persistent or recurrent pain.
Non-Union
One reason for continued pain is non-union, where the bones fail to fuse completely across the joint space. If the joint remains mobile, the original pain source is not fully eliminated, and the surgical stabilization has failed.
Misdiagnosis and Scar Tissue
Pain may also persist because the true source of the patient’s discomfort was misdiagnosed, meaning the SI joint was not the primary pain generator. The symptoms of SI joint dysfunction often overlap with other conditions like lumbar spine disorders, and operating on the wrong area will not resolve the problem. The formation of significant scar tissue post-operation can also contribute to chronic discomfort by irritating surrounding nerves and soft tissues.
Biomechanical Stress on Neighboring Joints
Fusing the SI joint eliminates motion at that segment, altering how forces are transferred through the pelvis and spine, creating a long-term biomechanical downside. This redistribution of load places increased stress on adjacent, unfused segments, a phenomenon known as Adjacent Segment Disease (ASD).
Stress on the Lumbar Spine
The most susceptible neighboring structure is the lumbar spine, specifically the L5-S1 segment. Increased mechanical loading on the lower lumbar spine can accelerate the degeneration of intervertebral discs and facet joints, potentially leading to new back pain or spinal instability. Biomechanical studies suggest SI joint fusion causes a minimal increase in range of motion at the L5-S1 segment, though the long-term clinical effect on ASD development is still being investigated.
Stress on the Hip Joints
The altered load transfer can also accelerate wear and tear on the hip joints. This may lead to earlier onset of hip osteoarthritis and the potential need for future procedures, such as a hip replacement. Resolving SI joint pain may inadvertently create a new pain problem in an adjacent area over time.