This retrospective multicenter study examined sagittal spinopelvic alignment in 214 adolescents and young adults with developmental L5–S1 spondylolisthesis. It compared six radiographic parameters against 160 asymptomatic controls to determine whether pelvic anatomy drives spinal deformity in this condition.
When you see a teenager with isthmic spondylolisthesis, the pelvic incidence on the standing lateral film tells you far more than just where they stand today.
A high PI (above ~65–70°) signals that the entire sagittal alignment is under stress — the lumbar lordosis is being driven up, the thoracic spine is compensating by flattening, and the shear load at L5–S1 is amplified by anatomy that will never change.
This paper is why we measure PI on every spondylolisthesis film: a high PI predicts higher slip grade and is the structural reason these patients progress. In surgical planning, restoring spinopelvic balance. Not just reducing the slip. Is the goal, because the deformity lives in the whole sagittal column, not just at one level.
PI became the cornerstone of spinal deformity analysis after this and related work, directly informing the SRS-Schwab classification and modern adult spinal deformity correction thresholds.
This retrospective multicenter study examined sagittal spinopelvic alignment in 214 adolescents and young adults with developmental L5–S1 spondylolisthesis. It compared six radiographic parameters against 160 asymptomatic controls to determine whether pelvic anatomy drives spinal deformity in this condition.
When you see a teenager with isthmic spondylolisthesis, the pelvic incidence on the standing lateral film tells you far more than just where they stand today.
A high PI (above ~65–70°) signals that the entire sagittal alignment is under stress — the lumbar lordosis is being driven up, the thoracic spine is compensating by flattening, and the shear load at L5–S1 is amplified by anatomy that will never change.
This paper is why we measure PI on every spondylolisthesis film: a high PI predicts higher slip grade and is the structural reason these patients progress. In surgical planning, restoring spinopelvic balance. Not just reducing the slip. Is the goal, because the deformity lives in the whole sagittal column, not just at one level.
PI became the cornerstone of spinal deformity analysis after this and related work, directly informing the SRS-Schwab classification and modern adult spinal deformity correction thresholds.