The diagnosis of meniscal lesions is a classic indication for knee MRI since the MRI invention. Traditionally, the axial, sagittal, and coronal images were used in the diagnosis. Because in old systems and technology used in the past, the limited number of sequences was used in the diagnosis and with thick cuts (4–5 mm). Now, high-field MRI and the advances in MRI technology had lessened the time used in each sequence and make much better resolution even with very thin cuts. Due to old MRI system limitations and meniscal orientation in axial plane parallel to the femoral and tibial articular surfaces, axial cuts were not an interest in meniscal tear diagnosis, unlike the sagittal and coronal planes. The sagittal and coronal planes can diagnose accurately most of the meniscal lesions, yet, in some cases, it can misdiagnose tears because it uses some indirect signs in diagnosis that could be non-specific in some cases. Moreover, the exact morphology and extent of the lesion are not readily seen in those planes and that raises the importance of the axial thin-cut fat-suppressed PD sequence in the diagnosis as it can overcome these limitations and has an added value in accurate diagnosis. The morphology of the tear is important not only in the management of the presence or absence of tear because the decision of suturing or resection of the affected horn depends on its morphology .
MRI sensitivity in the diagnosis of medial meniscal tears was found to be about 87–97% and specificity about 87–98% while for lateral meniscal tears sensitivity was 72–93% and specificity 89–99% according to previous studies . This range of difference in the results is due to the different types of sequences used in the diagnosis and the sample size in previous studies, as well as interobserver variability .
Araki et al. made a comparative study between 3D gradient-recalled acquisition in the steady state (GRASS) 0.7-mm thickness versus sagittal and coronal images and found that it had 97% sensitivity and 96% specificity .
Tarhan et al. also found that axial planes add more accuracy for the meniscal tear diagnosis with 79% accuracy for the medial meniscal tears and 71% for the lateral meniscus tears .
In another study done by Ohishi et al., he used 3D data and reconstructed axial images and found they are helpful in the diagnosis of tears. His study showed a high false positive rate in the diagnosis of medial meniscal tears and could not detect horizontal tears .
Gokalp et al. made a similar study comparing the sagittal, coronal, and axial images to arthroscopy. For sagittal PD WIs, the sensitivity was 90.62% and specificity 70.73% for the medial meniscal tears while for the lateral meniscus the sensitivity was 72.73% and specificity 77.1%. For axial images, the sensitivity was 97.3% for the medial meniscal tears and 84% specificity while for the lateral meniscal tears sensitivity was 95.65% and specificity 80.56% .
In our study, we compared the findings of thin axial images alone with arthroscopic findings. Of course, each MR study included sagittal and coronal images, but they were not included in the diagnosis of tears. Experienced musculoskeletal radiologists can diagnose all types of tears using axial images with more accurate diagnosis by using the sagittal and coronal cuts as well.
Axial PD WIs yield a high diagnostic performance with sensitivity of 96.3% for the medial and lateral meniscal tears and specificity of 100%. All lateral meniscal tears were accurately diagnosed by the axial images with 100% sensitivity and specificity.
A horizontal tear of the medial meniscus was missed in this study [out of three] because it was a small and thin tear running parallel to the axial plane taken in our study. Two other horizontal tears in medial meniscus were diagnosed by the axial images as they were large and thick dissecting the horizontal plane and so they readily appeared in the axial cuts. No horizontal tears encountered in the lateral meniscus.
The morphology of the different types of tear is very important in the management and not only in the classifications. Orientation of the lesion, gapping, direction, and different extensions are crucial in the decision making of either suturing the tear or doing meniscectomy, and this can only be assessed by the axial images.
One limitation of the study is that the time of scan was 6–8 min which was considered a relatively long duration, but it yields high diagnostic capability that weighs a long time. Using high field 3-T systems can reduce the acquisition time. Another limitation was that we did not use the sagittal and coronal images in the diagnosis which could give more accurate results with arthroscopy findings, but we wanted to emphasize the importance of the axial images.
In conclusion, axial PD WIs yield high diagnostic capability and give valuable information about the types of tears, and it is worth to add this sequence as a routine in knee MRI imaging together with the other conventional sequences but not to replace them.