Increased posterior tibial slope in patients with anterior cruciate ligament-deficient knees compared to knees with an intact anterior cruciate ligament and a degenerative medial meniscus tear: A radiographic comparative study.

Abstract

The aim of this study was to quantify the difference in posterior tibial slope (PTS) in patients with anterior cruciate ligament (ACL) deficiency compared to those with a degenerative medial meniscus posterior horn tear (dMMPHT). We hypothesised that patients with ACL deficiency would have a greater PTS compared to patients with dMMPHT. All consecutive patients diagnosed with ACL deficiency (ACL group) or a dMMPHT with an intact ACL (MM group) from 2016 to 2022 at a single centre were reviewed. PTS was measured using the medial tibial plateau and tibial mechanical axis on standard lateral knee radiographs. Linear regression analysis was completed to assess the correlation between PTS and age in both groups. Further sub-group analysis was undertaken according to age and sex of the study population. In total, 294 patients in the ACL group and 250 patients in the MM group were analysed. Age differed between the groups (ACL group: 29.5 ± 10.4 years vs. MM group: 38.7 ± 8.5 years, <i>p</i> < 0.001). Radiological evaluation demonstrated increased mean PTS in the ACL group compared to the MM group (10.1° ± 3.0 vs. 6.7° ± 2.6, <i>p</i> < 0.001). Regression analysis showed no significant correlation between the PTS and age in each group. When patients were subdivided into those younger than 30 years of age and those 30 years or older, there was no significant difference in the PTS in the ACL group. In contrast, younger patients had a steeper PTS compared to those 30 years or older in the MM group (7.5° ± 1.9 vs. 6.5° ± 2.7, <i>p</i> = 0.005). Patients with an ACL tear had a significantly higher PTS on standard lateral knee radiographs compared to those with dMMPHTs and a normal ACL. Elevated PTS may be a risk factor for ACL rupture. Level III, retrospective cohort study.