# Knee MRI Underestimates the Grade of Cartilage Lesions
## 2 Materials and Methods  
This retrospective cohort study was conducted on medical records of patients treated in the orthopaedic department of Leczna Hospital in Poland between September 2014 and February 2020. During this time, 190 consecutive knee arthroscopies with preoperatively obtained and stored MRI images and reports were performed. A bioethical committee at the Medical University in Lublin, with approval number KE-0254/262/2019, was obtained for the study. In addition, each patient signed a written consent concerning the use of medical data for clinical purposes without revealing personal data. Only examinations performed on 1.5 Tesla MRI with a full written report in the medical history were included in the study. MRI protocols were selected by radiology specialists based on an examination referral. In this study, we have not gained access to the referrals and had no influence on the MRI protocols or sequences used in the examination, which presents a common clinical setting. The MRI reports were prepared by 18 radiologists from 10 different MRI centres. There is no data concerning the experience or the field of interest of radiologists evaluating the images. The information of cartilage status was noted, and each articular cartilage deviation was noted in a written report. If no information on the cartilage defects was given, then the cartilage was regarded as a grade O as per the International Cartilage Repair Society (ICRS) [21; 22]. A grade 0 for cartilage defects which are not mentioned was assumed due to the fact that an orthopaedic surgeon reading an MRI report will consider the lack of mentioning of cartilage defects as a healthy cartilage. This assumption was made in 57 patients. Arthroscopic surgery was a gold standard for the estimation of MRI diagnostic accuracy. All the surgeries were performed by three surgeons specializing in sports knee surgery with an experience of 5-15 years, with a standard 30-degree optics in a standardized eight-step knee evaluation. Typical antero-lateral and antero-medialportals with accessory portals (when indicated) were utilized for the surgery. Indications for the surgery were made by the treating surgeon, based on the medical history, along with clinical and radiological findings. During arthroscopy, chondral lesions were graded 0-4 with the use of the ICRS classification system [21; 22]. Images presenting cartilage lesions are shown in Figures 1-4. Locations such as medial femoral condyle (MFC), lateral femoral condyle (LFC), medial tibial condyle (MTC), lateral tibial condyle (LTC), and patellofemoral joint (PFJ) were evaluated. All the tissues during the arthroscopy were visualised and examined with a probe. Images of all the intraoperative findings were taken during the surgery and stored in the hospital database. The data concerning the cartilage status during arthroscopy was obtained from operative notes.  
Figure 1: (**a**) Arthroscopic view of healthy smooth articular cartilage of medial femoral condyle (MFC) and grade I lesions of medial tibial condyle (MTC) with visible superficial lesions and softening of the cartilage; (**b**) healthy articular cartilage visible on MFC and grade I cartilage lesions in a sagittal proton density fat-suppressed sequence.  
Figure 2: (**a**) Arthroscopic view of grade II cartilage lesions with less than 50% of cartilage depth affected on lateral femoral condyle (LFC); (**b**) grade II cartilage lesion on MFC seen in a coronal proton density fat-suppressed sequence.