Outerbridge Classification

The Outerbridge classification is a grading system for joint cartilage breakdown:

Grade 0 - normal

Grade I - cartilage with softening and swelling

Grade II - a partial-thickness defect with fissures on the surface that do not reach subchondral bone or exceed 1.5 cm in diameter

Grade III - fissuring to the level of subchondral bone in an area with a diameter more than 1.5 cm  

Grade IV - exposed subchondral bone

Subchondral bone is the bone underneath the white joint cartilage.

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