Sacroiliac (SI) joint fusion is a minimally invasive procedure used to treat chronic lower back or buttock pain that comes from the sacroiliac joint—the joint that connects the spine to the pelvis. When this joint becomes unstable or arthritic, it can cause ongoing pain that doesn’t improve with conservative treatments. During the procedure, small implants are placed across the SI joint to stabilize and fuse the joint, reducing painful movement. It’s typically done through a small incision and often as an outpatient procedure. The goal is to decrease pain, improve stability, and help patients return to daily activities.