# Knee MRI Underestimates the Grade of Cartilage Lesions
## 4 Discussion
In our study, Kappa values for any anatomical location did not surpass 0.6, which strongly shows a discrepancy between MRI and arthroscopy findings. These findings are clearly represented on [PERSON]'s observer agreement charts. The severity of the cartilage lesion was grossly underestimated, which can significantly affect the planned surgical procedure during arthroscopy. Our study shows that even though MRI is the best available imaging modality for cartilage evaluation, it has significant weaknesses in regard to its specificity and sensitivity. It has a limited diagnostic accuracy for grade I-III chondral lesions. MRI showed the lowest sensitivity on the lateral tibial condyle, regardless of the lesion grade. This finding can be attributed to a small number of grade III and IV lesions, which are most apparent on the MRI. It is known that chondral lesions progress over time [42; 43]. Therefore, in our study, we have taken into consideration the time-lapse between the examination and surgery. However, no significant correlation between the time-lapse and the diagnostic accuracy was found for any anatomical location or grade of chondral lesions (\(p\) = 0.783). The ROC analysis was utilized to evaluate the diagnostic performance of MRI for the detection of any lesion, regardless of the lesion grade in specific anatomical locations. Only MFC and PFJ showed an acceptable diagnostic accuracy, with AUC exceeding 0.7. This shows that lesions in the lateral compartment of the knee can be omitted during an MRI examination. A systemic review by [PERSON] et al. [44] showed similar results. In our study, we have used only 1.5 T scanners for the examination. However, a study by [PERSON] et al. [45] suggests that 3 T scanners show a similar diagnostic performance as the standard MRI protocol. Therefore, some authors seek indirect methods of knee cartilage status evaluation. [PERSON] et al. [46] proposed the identification of early osteoarthritis which is not based on the cartilage status, but on visible bone marrow lesions and infrapatellar fat pad synovitis. Such an approach can be explained by the so-called satisfaction of the search [47] when the detection of abnormality can reduce the detectability of other intraarticular lesions. The bias of this study consists of the lack of access to MRI referrals. This could influence the low sensitivity and the accuracy of MRI in our study when no attention in the referral was put on cartilage evaluation. As shown by [PERSON] et al. [48], approximately 40% of MRI referrals may be totally inappropriate or uncertain. Moreover, some authors suggest that an MRI examination prior to the planned arthroscopic surgery does not change the treatment strategy [19]. The findings are supported by other researchers [49], however, if the MRI is ordered by an orthopaedic surgeon, it has a greater impact on the planned treatment [50] compared to a primary care physician. The accurate referral may incline the usage of cartilage dedicated sequences, which improves the overall diagnostic accuracy [51]. The experience and training of a radiologist performing the cartilage evaluation is also a factor which influences the diagnostic performance of the MRI [52]. In conclusion, the MRI is the best available modality for cartilage evaluation. However, it should be used with caution, and an underestimation of the cartilage defect severity should be taken into consideration when planning a surgical procedure. Chondral lesions identification is acceptable only in MFC and PFJ. Apart from healthy cartilage and grade IV lesions, the MRI results should be suspected of severity underestimation.