High variability of tibial slope measurement methods in daily clinical practice: Comparisons between measurements on lateral radiograph, magnetic resonance imaging, and computed tomography.

Background: Tibial slope measurements are important in guiding clinical decisions in the field of orthopedic surgery. However, there are multiple techniques across different medical imaging modalities and little is known about its impact on result and validity of the measurement. Therefore, the purpose of this study was to compare tibial slope measurements from lateral radiographs, magnetic resonance imaging (MRI) and computed tomography (CT) scans in order to better assess the clinical significance of measured tibial slope values.

Methods: Twenty patients with complete medical imaging (lateral radiographs, MRI, CT scans) undergoing anterior cruciate ligament revision surgery were included. The tibial slope of the medial and lateral plateau were measured and compared using the methods of Dejour et al. and Utzschneider et al. on lateral radiographs, by Hudek et al. and Hashemi et al. on MRI and CT scans, and by Zhang et al. on three-dimensional reconstructions of CT scans.

Results: Mean differences up to 5.4 ± 2.8° (P < 0.05) and 4.9 ± 2.6° (P < 0.05) between different measurement methods were found for the medial and lateral tibial slope, respectively. Depending on how the tibial shaft axis was defined, significant differences between the respective measurement methods and a relevant degree of variability were identified. Pearson correlation coefficients between the measurement methods varied distinctly from moderate to strong correlations.

Conclusions: Tibial slope measurements have a high degree of variability and inaccuracy between imaging modalities and different measurement methods. Care must be taken when deciding on indications based on individual modality measurements.