Quadrilateral Segmental Analysis (QSA): A Calibration-Free Geometric Method for Detecting Lumbar Spondylolisthesis

Background/Objectives: On standing lateral radiographs, millimetre measurements of vertebral slip depend on magnification and calibration; slip percentage is scale-free but is usually reported in coarse Meyerding grades. In this exploratory derivation study, we introduce quadrilateral segmental analysis (QSA), a calibration-free geometric method for detecting anterolisthesis.

Methods

In 50 patients with degenerative spondylolisthesis from the PROGRES cohort, a blinded observer drew the L1–S1 superior endplate lines on standing radiographs; an automated pipeline computed the diagonal ratio K and the posterior angles of each quadrilateral formed by adjacent lines. The annotation was performed by a single observer; its reproducibility was not assessed, and its sensitivity to annotation error was simulated. The reference standard was an adjudicated two-radiologist classification (κ = 0.916). Segments outside the anterior-translation domain (negative shear; n = 90) were not graded further; the remaining 160 were analysed with patient-cluster bootstrap and leave-one-patient-out validation.