2025 ISAKOS Biennial Congress Paper
Comparison of Posterior Tibial Slope Profiles in Anterior Cruciate Ligament Patients Using Magnetic Resonance Imaging and Radiography: Multiple Revisions Versus Successful Primary Reconstruction
Mahmut Enes Kayaalp, MD, Assoc. Prof., Istanbul TURKEY
Jumpei Inoue, MD, Pittsburgh, PA UNITED STATES
Efstathios Konstantinou, MD, MSc, Pittsburgh, PA UNITED STATES
Thorkell Snaebjörnsson, MD, Reykjavik ICELAND
Jon Karlsson, MD, PhD, Prof., Mölndal SWEDEN
Volker Musahl, MD, Prof., Pittsburgh, Pennsylvania UNITED STATES
University of Pittsburgh, Pittsburgh, Pennsylvania, UNITED STATES
FDA Status Not Applicable
Summary
This study compares posterior tibial slope (PTS) in patients with multiple revision ACL reconstructions and those with successful primary ACL reconstructions, finding that a higher radiographic medial PTS is associated with revision surgeries, while lateral PTS on MRI does not correlate with this risk, suggesting limited utility in using MRI-based lateral PTS for clinical decision-making.
Abstract
Introduction
An increased posterior tibial slope (PTS) is a widely recognized risk factor for ACL graft failure. However, conflicting results have been reported regarding medial versus lateral PTS on MRI and medial PTS on radiography within similar patient groups. These discrepancies may be due to various factors, including patient-specific variations in proximal tibial morphology. This study aims to explore and compare the differences in PTS between patients undergoing multiple revision ACL reconstructions and those with successful primary ACL reconstructions, using both MRI and radiography.
Methods
A ten-year chart review identified 504 patients who underwent revision ACL reconstruction (ACLR), of which 94 (19%) involved multiple revisions. After excluding 16 patients, 78 were included in Group A, while Group B consisted of 78 matched unilateral primary ACLR patients. A successful ACLR was defined as having undergone primary ACL surgery with at least two years of follow-up and no signs of graft reinjury. Medial PTSs were measured using radiographs, and both medial and lateral PTSs were assessed using MRI. Patients were categorized into high-risk and normal PTS groups based on literature-defined cut-offs: ≥13˚ for radiographic PTS, >7˚ for lateral PTS on MRI, and >5˚ for medial PTS on MRI. Differences between the groups were analyzed, and PTS measurement reliability was assessed by two blinded raters.
Results
Group A (multiple revision ACLR) had a significantly higher radiographic PTS (12.4±3.4) compared to Group B (11.3±3, p=.04). In Group A, 49% had a PTS of ≥13˚, versus 35% in Group B (p=.07). A PTS of ≥16˚ was associated with an increased risk of having undergone revision surgery (Odds ratio=2.9, p=.03). No significant differences were found between groups in medial or lateral MRI PTSs or PTS asymmetry. The occurrence of a PTS >7˚ for the lateral PTS on MRI and >5˚ for the medial PTS on MRI was similar in both groups. There was a moderate correlation between radiographic PTS and medial PTS on MRI in both groups (r=0.49, p<.001 for Group A; r=0.42, p<.001 for Group B). Lateral PTS on MRI did not correlate with radiographic PTS in Group B; however, it showed a weak correlation in Group A (r=0.29, p=.01). Interobserver reliability was excellent (Cronbach’s α=0.902 and 0.851), as was intraobserver reliability for both radiographic and MRI measurements (Cronbach α=0.924 and 0.852), respectively.
Conclusion
The data from this study shows that the primary significant difference between the ACL-injured patient cohorts was the radiographic medial PTS, which was statistically higher in the revision ACL cohort compared to the primary reconstruction cohort. Despite this difference, the prevalence of a ≥13˚ PTS angle was similar between the groups, suggesting that patients with high-risk PTSs are also common among those with successful ACLR. Additionally, the lateral PTS measured on MRI did not differ between the groups and did not correlate with the radiographic medial PTS. This indicates that lateral PTS on MRI may not be a reliable risk factor or decision-making tool in the management of ACL-injured patients.