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



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.


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 (ATSdiff) 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.


Under the axis protocol, ATS was positively correlated with PTS in both the ACL-injured and ACL-intact groups (p < 0.001). Under the plateau protocol, no correlation was observed in the ACL-injured group. In the ACL-intact group, no correlation was observed for lateral ATS, and a negative correlation was observed for medial ATS (p = 0.001). ATSdiff was positively correlated with PTS (p < 0.001), indicating that the two protocols varied greatly in those with a steep PTS. Trigonometric analysis showed that a steep PTS influenced the measurement of ATS under the plateau protocol but not the axis protocol. Intra- and interobserver reliability tests showed good-to-excellent strength of reliability for the ATS measurement under the axis protocol.


ATS measured under the axis protocol was positively correlated with PTS, indicating that a steep PTS was associated with a worse anatomic tibiofemoral relationship. The axis protocol for ATS measurement is a promising method for clinical use since it is not influenced by PTS and reflects the global position of the tibia.

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Fig. 1
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Fig. 3



Anterior cruciate ligament


Anterior cruciate ligament reconstruction


Anterior tibial subluxation

ATSdiff :

The difference in the ATS value measured under the two protocols


Magnetic resonance imaging


Posterior tibial slope


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This study was supported by grants from the National Natural Science Foundation of China (no. 82072403).

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Authors and Affiliations



ZZ drafted the manuscript. CW and JW participated in the design of the study. XP and PM completed data acquisition and designed the measuring procedure in the software. LM and ZH developed the tables and figures in this study and participated in drafting the manuscript. QZ contributed to the acquisition and evaluations of MRIs from outpatient department. QZ, CW and JW contributed to data interpretation. XP shaped the manuscript and improved the English language writing. All the authors have read and approved the final manuscript.

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Correspondence to Cheng Wang or Jian-quan Wang.

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The author(s) declare that they have no competing interests.

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Formal approval of this study (no. M2020433) was obtained from the Ethics Committee of Peking University Third Hospital (No. 49, Huayuanbei Road, Haidian District, Beijing, China).

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Zhang, Zy., Pan, Xy., Maimaitijiang, P. et al. Anterior tibial subluxation measured under a modified protocol is positively correlated with posterior tibial slope: a comparative study of MRI measurement methods. Knee Surg Sports Traumatol Arthrosc 30, 3350–3360 (2022).

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  • Anterior cruciate ligament
  • Posterior tibial slope
  • Anterior tibial subluxation
  • Injury
  • Correlation
  • MRI
  • Methodology