Posterior Tibial Slope Measurements of the Medial and Lateral Plateaus Vary Widely Between Magnetic Resonance Imaging and Computed Tomography.

PURPOSE

To compare posterior tibial slope (PTS) measurements of the medial tibial plateau (MTP) and lateral tibial plateau (LTP) on magnetic resonance imaging (MRI) versus computed tomography (CT) to determine the agreement of measurement between imaging modalities.

METHODS

Patients aged 15 to 65 years with concurrent MRI and CT imaging were initially included. Knees with significant arthrosis (Kellgren-Lawrence grade >2), proximal tibia fracture, or artifact obscuring visualization were excluded. Two independent raters measured PTS of the MTP and LTP on paired MRI and CT. Inter- and intrarater reliability were assessed using the intraclass correlation coefficient (ICC). Intermethod agreement was assessed using ICC and Bland-Altman analyses. An acceptable Bland-Altman limit of agreement (LOA) was set at ±2°, requiring 95% of measurement differences between imaging modalities to fall between ±2° for an acceptable level of agreement.

RESULTS

Forty-six knees in 45 patients met final inclusion criteria. Inter-rater reliability was good for MRI (ICC 0.78-0.83) and moderate to good for CT (ICC 0.64-0.80) studies. Intrarater reliability was moderate to excellent (ICC 0.64-0.94). Intermethod agreement between MRI and CT was poor at the MTP (ICC 0.34-0.42) and moderate at the LTP (ICC 0.59-0.70). Bland-Altman analysis demonstrated high variability of PTS measurements between MRI and CT: 0.16° (95% LOA -6.10° to 6.41°) for MTP for Rater 1; 0.22° (95% LOA -5.01° to 5.45°) for LTP for rater 1; -0.95° (95% LOA -7.22° to 5.33°) for MTP for Rater 2; -0.99° (95% LOA -6.48° to 4.85°) for LTP for rater 2, with only 47.83% to 60.87% of measurement differences falling within the predetermined acceptable LOA of ±2°.

CONCLUSIONS

Although the inter- and intrarater reliability was moderate to excellent, the degree of agreement between PTS measurements on MRI and CT was highly variable at both medial and lateral plateaus. Although some variability may have been due to the study's limitations, PTS measurements at individual plateaus may not be interchangeable between MRI and CT.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.