Outerbridge Classification

Written by Dr Sheila Strover on March 14, 2025

The Outerbridge classification is a grading system for joint cartilage breakdown in the knee.

Normal joint cartilage of femur (below) and patella (above) in the knee joint. Grade 0 on the Outerbridge scale

Grade I - softening of the patellar cartilage, which can be dimpled with a rounded probe (see top left of this image).

Grade III damage of the patella on the same grading system. The patellar cartilage has become fibrillated and note that the tibia is showing exposed yellowish bone, which would be a grade IV.

Grading joint cartilage damage (Outerbridge)

By recording the Outerbridge Grade, the surgeon will have a simple record for later comparison in case of deterioration or improvement in the joint cartilage.

"....The system is largely used to facilitate communication between surgeons....[It ]....is also important for surgical planning and patient education...."

Slattery C et al

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

Other relevant links on KNEEguru

A-Z Keywords -

Cartilage damage, Noyes classification

Flowchart -

Dr Sheila Strover - 2018 - Arthritis Flowchart

Primer -

Dr Sheila Strover - 2016 - Osteoarthritis Management Options

eBook -

Dr Sheila Strover - Knee arthritis interventions when you are too young for a total knee replacement

End of links