Pelvic Fixation Using S2AI and Triangular Titanium Implants (Bedrock Technique)

Pelvic fixation is becoming an increasingly important caudal anchor point for long lumbar constructs, high-grade spondylolisthesis, fixation of sacral fractures, and support for 3-column osteotomies, by adding lumbosacral fixation anterior to the McCord pivot point. Iliac bolts were once common but have become less favorable due to screw head irritation and complications associated with connecting rods. S2-alar-iliac (S2AI) screws have been shown to achieve equivalent anchoring strength of constructs to the pelvis, while being lower profile and in line with the lumbar instrumentation. More recently, surgeons have noted the potential for S2AI screws to toggle and loosen, commonly in the softer sacrum, leading to caudal anchor failure and possible pseudarthrosis. The addition of triangular titanium implants to augment S2AI screws (bedrock technique) is a relatively new adaptation to reduce toggling on the S2AI screw and improve the overall stability of the pelvic fixation. Video 1 shows the placement of an S2AI screw and triangular titanium implant for pelvic fixation. The patient is a 68-year-old woman who presented with flat back syndrome, spinal stenosis, degenerative spondylolisthesis, pseudarthrosis of previously instrumented levels, and bilateral sacroiliitis. She underwent posterior instrumentation and fusion of L1 to S1 with pelvic fixation, open bilateral sacroiliac joint fusion, and multilevel Smith-Peterson osteotomies and transforaminal lumbar interbody fusions.