# Knee MRI Underestimates the Grade of Cartilage Lesions
###### Abstract  
Purpose: This study was conducted in order to evaluate the clinical utility of MRI in detecting cartilage lesions and its dependence on anatomical location and lesion grade. Methods: A retrospective analysis of MRI reports and arthroscopic findings was performed on 190 consecutive patients treated in one orthopaedic department. MRI protocols were prepared by 18 radiologists from 10 different MRI centers with the use of 1.5 T magnets. The image protocols were selected by reading radiologists. Four hundred and fifty-three chondral lesions in five anatomic locations were identified during this study and graded according to the ICRS classification. Sensitivity, specificity, receiver operating characteristic (ROC), and [PERSON]'s observer agreement charts were utilized to evaluate the diagnostic performance. Results: Only approximately 30% of MRI showed an adequate cartilage status in all anatomical locations. The sensitivity ranged from 92% in healthy cartilage to 5% in grade I lesions. The specificity differed also grossly depending on the lesion grade, reaching 96.5% in grade four lesions and 38% in healthy cartilage. The medial compartment [PERSON]'s observer agreement charts show a gross underestimation of cartilage lesions, and the area under the curve (AUC) of ROC surpasses 0.7 only in the medial femoral condyle and patella-femoral joint. Overall, the medial compartment accuracy was significantly higher than the lateral compartment. The MRI showed correspondence of its diagnostic performance with cartilage lesion severity. Conclusion: MRI underestimates the extent of cartilage injury and evaluation of cartilage defects based on MRI should be taken with caution by orthopaedic surgeons in planning surgery. Surgical planning on MRI should take cartilage lesions under consideration, even if no cartilage lesions are reported on the MRI. MRI; cartilage; knee; cartilage lesion +
Footnote †: journal:saturation transfer (gagCEST), diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), and relaxometry measurements [7]. Such techniques enable the differentiation between a healthy and repaired cartilage [8], can correspond with glycosaminoglycans concentration [9; 10; 11], or enable the quantitative monitoring of macromolecules in early osteoarthritis [12]. Therefore, the techniques in question might be suitable for the detection and evaluation of early cartilage changes as well as an accurate cartilage evaluation. However, the techniques present certain limitations. First, the availability of specialized techniques is limited. Moreover, dGEMRIC requires gadolinium administration and potential side effects can be encountered [13]. Joint effusion can interfere with the gagCEST evaluation due to the presence of glycosaminoglycans in the synovial fluid [14]. Even after introducing a 3D MRI [15], which exhibits high sensitivity to grade III and IV lesions [16] and is more accessible than the compositional techniques, the 1.5 T MRI examination remains a workhorse for cartilage evaluation. Of special interest to the orthopaedic surgeons is the estimation of cartilage defect grade, size, and location, which strongly influences the decision of switching from a conservative to surgical treatment [17; 18]. However, some authors suggest that the information obtained by MRI does not change scheduled arthroscopic surgeries and does not affect the overall treatment costs [19]. To date, there is a sparse number of articles presenting the diagnostic efficacy of MRI regarding the grade and lesion location in a typical clinical setting. A great number of papers published on the subject depend on the evaluation performed by a musculoskeletal radiologist, who is trained specifically for such diagnosis [20]. However, in many instances, the MRI is evaluated by a general radiologist, or often a referring orthopaedic surgeon that has no knowledge whether the radiologist specializes in musculoskeletal disorders.