Correlation of medial tibial slope and lateral tibial slope measured on radiographs and magnetic resonance imaging in patients with anterior cruciate ligament injury

Objectives: The study aimed to investigate the correlation between medial tibial slope (MTS) and lateral tibial slope (LTS) on magnetic resonance imaging (MRI), MTS measured by different imaging, and the intra- and interobserver reliability of measurements between reviewers with gaps of experience over 10 years. Patients and methods: This retrospective study included 97 patients (93 males, 4 females; mean age: 30.8 +/- 8.3 years; range, 17 to 49 years) with anterior cruciate ligament (ACL) injuries who subsequently underwent double-bundle ACL reconstruction by a single surgeon between January 2005 and December 2014. The MTS was measured on lateral knee radiographs, and MTS and LTS were measured on MRIs. Three different reviewers, including a postgraduate year doctor, an orthopedic resident, and an attending orthopedic surgeon, performed the measurements. Each reviewer measured the slope of the same image three times. The correlations of MTS on radiographs and MTS/LTS on MRIs were calculated. Intra- and interobserver reliability were evaluated. Results: The average MTS and LTS measured on MRI were not significantly different (6.4 degrees and 6.9 degrees, respectively; p=0.268) and exhibited a moderate positive correlation (r=0.544, p<0.001). The average MTS on radiographs was significantly greater than that on MRI (10.5 degrees and 6.4 degrees, respectively; p<0.001) with a low positive correlation (r=0.480, p<0.001). The intraobserver reliability of the postgraduate year doctor, the orthopedic resident, and the attending orthopedic surgeon were moderate to excellent. The interobserver reliability of MTS on radiographs was excellent (intraclass correlation coefficient [ICC]=0.925; p<0.001). The interobserver reliability of MTS on MRI as well as LTS on MRI was good (ICC=0.755 and 820, respectively; all p values <0.001). Conclusion: Average MTS and LTS measured on MRI in patients with ACL injury exhibited a moderate positive correlation. The average MTS measured on radiographs was significantly greater than that on MRI with a low positive correlation.