2025 ISAKOS Biennial Congress Paper
Posterior Tibial Slope as a Risk Factor for Anterior Cruciate Ligament Graft Re-Rupture: A Great Concept but Impossible to Accurately Measure
Wahid Abdul, BSc(Hons), MBBCh, MRCS, FRCS(Tr&Orth), MSc(SEM), Exeter UNITED KINGDOM
Mary Jones, MSc, Grad. Dip. Phys., Richmond, Surrey UNITED KINGDOM
David Johannes Haslhofer, MD, Linz AUSTRIA
Arman Motesharei, PhD, London UNITED KINGDOM
Emmanouil Astrinakis, MD, London UNITED KINGDOM
Justin Lee, MB BS, FRCR, London UNITED KINGDOM
Simon Ball, MA, FRCS(Tr&Orth), London, Middlesex UNITED KINGDOM
Andy Williams, MBBS, FRCS(Orth), FFSEM(UK), London UNITED KINGDOM
Fortius Clinic London, London, UNITED KINGDOM
FDA Status Not Applicable
Summary
Posterior Tibial Slope (PTS) measurements have a high degree of variability and inaccuracy between imaging modalities and raters with no significant difference in measurements according to different CT reconstructions observed.
Abstract
Introduction
Posterior Tibial Slope (PTS) ≥12º is a risk factor for Anterior Cruciate Ligament (ACL) and ACL rupture. Several measurement techniques have been reported with varying degrees of accuracy.
Aims:
Investigate whether sagittal series on MRI and CT reconstructed with respect to the axial series to either, parallel to the ACL or perpendicular to the posterior femoral condylar axis (PFCA), affect PTS measurements.
Methods
Twenty patients undergoing revision ACL surgery between November 2019 and September 2022 were included. Medial PTS (MPTS) and lateral PTS (LPTS) were measured and compared using the method of Hudek et al. on sagittal MRI, initial sagittal CT acquisition, sagittal CT reconstructed to correspond to MRI and sagittal CT reconstructed perpendicular to PFCA.
Results
MRI produced greater mean PTS measurements (MPTS 5.88º, LPTS 7.57º) compared to different CT reconstructions (MRI alignment: MPTS 5.26º LPTS 6.35º; PFCA alignment: MPTS 5.09º LPTS 5.83º). Mean LPTS measurements were greater than MPTS measurements across all imaging modalities but only significant for MRI (p=0.01). No significant difference was observed between PTS measurements for CT as per MRI or perpendicular to PFCA. Intraclass correlation coefficient demonstrated good agreement (0.64) for LPTS measurements on MRI but poor agreement for MPTS measured on CT orientated to MRI (0.15) and perpendicular to PFCA (0.16).
Conclusion
PTS measurements have a high degree of variability and inaccuracy between imaging modalities and raters with no significant difference in measurements according to different CT reconstructions. One must take great care with PTS measurements when considering slope-changing osteotomy during revision ACL surgery.
Level of evidence: IV.
Keywords: Posterior Tibial Slope, Measure, Anterior Cruciate Ligament, Graft re-rupture