Assessing tibial slope measurements: A study of methodological consistency and correlation with ACL rupture.

Background: The tibial slope has emerged as a significant risk factor for anterior cruciate ligament (ACL) injuries and ACL graft failure. The lack of uniformity tibial slope measurement methods complicates clinical applications and research comparisons. This study aims to evaluate the correlation and reproducibility of different tibial slope measurement methods and their association with ACL rupture.

Hypothesis: We hypothesized that the four tibial slope measurement methods (ACTS, PCTS, PTS, and MTS) would show strong correlations with each other and that patients with ACL injuries would exhibit significantly higher tibial slopes compared to controls, regardless of the measurement technique.

Methods: A retrospective analysis was conducted on 100 patients, divided into two groups: 50 with ACL injuries and 50 with intact ACL. Tibial slope was measured on conventional lateral X-ray using four methods: Anterior Cortical Tibial Slope (ACTS), Posterior Cortical Tibial Slope (PCTS), Proximal Tibial Slope (PTS), and Mechanical Tibial Slope (MTS). A correlation analysis, including a correlation matrix and linear regression analysis was performed to evaluate the correlation between the measurement methods. Additionally, tibial slope values between the ACL-injured group and the intact ACL group were compared using statistical tests such as Student's t-test and Z-test. Intra- and inter-observer reliability were assessed using the intraclass correlation coefficient (ICC).

Results: The mean tibial slope varied depending on the measurement method, with the ACTS showing the highest values and PCTS the lowest. High correlation coefficients (R > 0.80) were observed between all methods, with the strongest correlation found between PTS and MTS (R = 0.933) and the lowest between ACTS and PCTS (R = 0.809), the linear regression analysis showed a strong linear relationship between all methods. Intra- and inter-observer reliability was excellent (ICC > 0.9422). Comparative analysis between the ACL-injured group and the intact ACL group revealed a statistically significant increase in tibial slope in the ACL-injured group, regardless of the measurement method.

Conclusion: The tibial slope measurements across the four measurements methods (anterior cortex, proximal tibial slope, posterior cortex and mechanical axis) are significantly correlated. The largest discrepancies are observed in measurements based on the anterior cortex. The reproducibility is satisfactory both intra- and inter-observer. A statistically significant increase in tibial slope is observed in the knees with an ACL injury, regardless of the measurement method used, reinforcing its role as a crucial risk factor in ACL rupture.

Level of evidence: III; Retrospective cohort study.