Fig. 2

Normal cartilage and different grade lesions for the SPGR and T2 sequences. a and b show the five-layered cartilage structure of the tibial plateau and the three-layered cartilage structure of the femoral condyle. For the grade 1 cartilage lesion (arrow) in c, a low signal intensity for the cartilage distinctly appeared. The cartilage lesion (arrow) in d was covered by joint effusion, and the border between the cartilage and the joint effusion could not be distinguished with the T2 sequence. The articular cartilage layer disappeared, and the defect was less than 50% of the thickness of normal cartilage for a grade 2 cartilage lesion (arrow in e). The T2 sequence shown in f also shows a mixed signal for a cartilage lesion (arrow) and joint effusion. g shows a grade 3 patellar cartilage lesion (arrow) with a defect of up to 50% of the thickness of normal cartilage. h shows severe wear of the cartilage of the femur, tibia and patella, which is considered to be a grade 4 cartilage lesion, and the subchondral bone marrow exhibits a cystic or patchy high signal