= pathologic softening of patellar cartilage leading to defects of surface (chondrosis) / osteoarthritis

Cause: trauma, tracking abnormality of patella

• anterior knee pain
• asymptomatic (incidental arthroscopic diagnosis)

MR (60% sensitive, 84% specific, 73% accurate):

• focal areas of increased T2 / PD signal intensity of cartilage
• partial / full-thickness cartilage loss
• underlying marrow / bone reactive changes