Background
The tibiofemoral angle (TFA), lateral distal femoral angle (aLDFA), medial proximal tibial angle (aMPTA) and joint line congruence angle (JLCA) are important variables for assessing knee alignment and is used in various applications, including evaluating knee status, pre-operative planning, and post-operative evaluation.
Purpose
To compare the reliability of measuring the TFA, aLDFT, aMPTA, and JLCA by evaluating the angle measurements in long leg radiographs (LLR) and MRI.
Methods
The retrospective study included patients aged 18-50 years who had knee MRI scans together with LLR. Two orthopedics surgeons measured TFA, aLDFA, aMPTA, and JLCA from both modalities in random sequences. The paired t-test was used to compare angles from these two modalities. The Bland-Altman analysis was used to evaluate the agreement and bias. Intraclass correlation coefficients(ICC) were calculated to consider intra- and interobserver reliability and reproducibility.
Results
Fifty-seven knees were included. TFA in MRI images was significantly larger(7.28±4.05 vs 4.81±2.56 degrees, P<0.001). For the other angle, aLDFA and JLCA in MRI images were significantly smaller (77.40±3.08 vs 80.61±3.69, P<0.001 and 1.91±1.35 vs 2.56±1.65, P=0.017 respectively). The aMPTA was not significantly different between the two modalities (87.02±3.87 vs 87.84±3.86, P=0.220). Intraclass coeffiecient for intraobserver is in good agreement for TFA for MRI (0.82) and LLR (0.87).
Conclusion
The measuring TFA, aLDFA, aMPTA, and JLCA angle cannot be reliably reproduced between individuals comparing MRI and LLR. LLR is important for evaluating the alignments of the knees.