The lumbosacral junction is a susceptible transition point between the mobile lumbar spine and the rigid pelvis. Already subject to high rates of pathology, this level can experience up to 67-69% radiographic adjacent segment degeneration following instrumentation with long constructs terminating at L5. Studies have shown that up to 22 % of adolescent scoliosis constructs terminating in the lower lumbar spine required revision within a 15-year follow up period. The sacropelvis is often included in cases of deformity correction including those requiring osteotomy, high grade spondylolistheisis, and “long” thoracolumbar constructs. What constitutes a long posterior construct, and when sacropelvic fixation is required are unclear at this time, and the optimal sacropelvic fixation technique for varying construct lengths has yet to be determined.

Biomechanical and clinical evidence supports that iliac screws remain the strongest, most definitive method of sacropelvic fixation. However, iliac screws also may increase operative time, blood loss, postoperative sacroiliac (SI) joint pain, and rarely neurovascular injury. Given the associated morbidity, iliac screws are not currently considered “the standard of care” for all long lumbar and thoracolumbar constructs. Understanding the impact that construct length, construct type, and loading direction have on kinematics of the base of the spine is in important factor in finding optimal solutions for each surgical intervention. This project aims to elucidate the relationship of all these variables.