"grade 0: normal cartilage"
"grade 1: increased T2 signal intensity of morphologically-normal cartilage not orientated at 55° to the external magnetic field"
"grade 2a: superficial partial-thickness cartilage defect"
"grade 2b: deep partial-thickness cartilage defect >50% of total articular surface thickness"
"grade 3: full-thickness cartilage defect"