Legaye et al. (1998) introduce pelvic incidence as a fixed anatomical parameter and ask whether it governs spinal sagittal alignment. Using standing radiographs in 49 normal adults and 66 scoliotic women, they quantify relationships among pelvic and spinal sagittal parameters. They derive predictive equations for lumbar lordosis and establish pelvic incidence as the anchor of the entire spinopelvic system.
Every lumbar fusion and osteotomy you plan depends on a number this paper defined.
Before 1998, sagittal shape classifications were purely descriptive — no one had shown that a single anatomical constant predicted how much lordosis a given patient's spine requires. This paper proved that pelvic incidence sets the target: high incidence demands high lordosis, and mismatch drives pain, dysfunction, and mechanical failure.
In clinic: measure pelvic incidence on every preoperative long-cassette film. If PI minus lumbar lordosis exceeds 10°, the patient is at high risk for adjacent segment disease and poor functional outcomes after fusion. This threshold, now codified in the SRS-Schwab classification, traces directly back to the correlation chain established here.
For scoliosis patients specifically, remember that high Cobb angles and apical rotation restrict the pelvis's ability to compensate. The more severe the curve, the less lordosis the pelvis can generate, and the harder it is to achieve economical sagittal balance after correction.
Legaye et al. (1998) introduce pelvic incidence as a fixed anatomical parameter and ask whether it governs spinal sagittal alignment. Using standing radiographs in 49 normal adults and 66 scoliotic women, they quantify relationships among pelvic and spinal sagittal parameters. They derive predictive equations for lumbar lordosis and establish pelvic incidence as the anchor of the entire spinopelvic system.
Every lumbar fusion and osteotomy you plan depends on a number this paper defined.
Before 1998, sagittal shape classifications were purely descriptive — no one had shown that a single anatomical constant predicted how much lordosis a given patient's spine requires. This paper proved that pelvic incidence sets the target: high incidence demands high lordosis, and mismatch drives pain, dysfunction, and mechanical failure.
In clinic: measure pelvic incidence on every preoperative long-cassette film. If PI minus lumbar lordosis exceeds 10°, the patient is at high risk for adjacent segment disease and poor functional outcomes after fusion. This threshold, now codified in the SRS-Schwab classification, traces directly back to the correlation chain established here.
For scoliosis patients specifically, remember that high Cobb angles and apical rotation restrict the pelvis's ability to compensate. The more severe the curve, the less lordosis the pelvis can generate, and the harder it is to achieve economical sagittal balance after correction.