Anterior tibial subluxation measured under a modified protocol is positively correlated with posterior tibial slope: a comparative study of MRI measurement methods

Purpose Anatomic factors, such as posterior tibial slope (PTS) and anterior tibial subluxation (ATS) obtained by quantitative measurement, have been proposed as predictors for clinical outcomes of anterior cruciate ligament (ACL) reconstruction. However, the correlation between PTS and ATS is controversial, and the method for quantitative ATS measurement remains unsettled. This study aimed to identify the correlation between PTS and ATS in patients with injured and intact ACLs and compare the two ATS measuring protocols. Methods This study included 128 ACL-injured and 176 ACL-intact patients with no concomitant ligament injuries. PTS and ATS were measured on sagittal MRI. ATS was measured using two measuring protocols, including the modified protocol using the longitudinal tibial axis (axis protocol) and the established protocol using a line perpendicular to the tibial plateau (plateau protocol). Correlation analyses between PTS and ATS and between PTS and the difference in the ATS value measured under the two protocols (ATS diff ) were performed. The difference between the two ATS measuring protocols was further analyzed by trigonometric analysis. Intra- and interobserver reliability tests were performed for the axis protocol. Results Under the axis protocol, ATS was positively correlated with PTS in both the ACL-injured and ACL-intact groups ( p