Summary
The aim of this study was to determine medial and lateral tibial slope on MRI in knee dislocations >=KD III, isolated ACL injuries, isolated PCL injuries, and ACL re-ruptures, and to compare the results with a degenerative medial meniscus tear control group.
Abstract
High tibial slope (TS) leads to increased forces on the anterior cruciate ligament (ACL). Low TS leads to increased forces on the posterior cruciate ligament (PCL). The influence of TS on multiligament injuries involving both cruciate ligaments has not been determined. Most studies perform measurements of TS using lateral radiographs, not distinguishing between medial and lateral TS. The aim of this study was to determine medial and lateral TS on MRI in knee dislocations >=KD III, isolated ACL injuries, isolated PCL injuries, and ACL re-ruptures and to compare the results with a degenerative medial meniscus tear control group.
The study is a retrospective case-control study. An a-priori power analysis revealed that the minimum sample size of 45 participants in all groups was required to obtain a power of 0.80. Lateral and medial TS measurements were taken in 50 patients per group with knee dislocations KD>=III, isolated ACL ruptures, isolated PCL ruptures, ACL re-ruptures, and degenerative medial meniscus tears (control group). Measurements were performed according to Hudek et al. on T1 weighting MRIs. To determine inter- and intra-rater agreements all measurements were performed twice by two blinded raters at two different timepoints. Data normality was confirmed by Shapiro-Wilk-Test. A t-test was used to compare each study group with the control group. Significance was set at p<0.05.
Lateral TS was significantly decreased in >=KDIII (4.2°±3.5°), isolated ACL ruptures (4.5°±3.6°), and isolated PCL ruptures (3.5°±3.6°) compared to the control group (6.7°±2.7°). Medial TS was significantly decreased in >=KDIII (3.7°±3.8°) and isolated PCL ruptures (3.5°±3.2°) compared to the control group (5.3°±2.4°). In isolated ACL ruptures (4.1°±4.2°), medial TS was not different compared to the control group. In ACL re-ruptures lateral TS (6.4°±3.1°) and medial TS (4.9°±3.0°) were not different compared to the control group. Interestingly, among the 50 patients with ACL re-ruptures, no patient had a medial TS >=12°, and only 2 patients had a lateral TS >=12°.
Based on the results of this study, decreased medial and lateral TS are associated with an increased risk of >=KDIII injuries and isolated PCL ruptures. In contrary to the literature, decreased lateral TS was associated with an increased risk of isolated ACL rupture. Medial TS did not influence the risk of isolated ACL rupture. Increased medial TS/lateral TS ratio might be a risk factor for ACL rupture. Medial and lateral TS did not influence the risk of ACL re-rupture, although it might be relevant in individual cases. The results of this study compared to current literature suggest, that especially the risk of ACL re-rupture might be multifactorial. Coronal and axial alignment, shape of the femoral condyle, and related injuries must be considered to create more valid predictions on injury patterns.