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

Page updated January 2024 by Dr Sheila Strover (Clinical Editor)

Outerbridge Grade 0 cartilage - normal patellar cartilage


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

Outerbridge Grade I - Chondromalacia or softening of the patellar cartilage


Grade I - softening of the patellar cartilage, which can be dimpled with a rounded probe.

Outerbridge Grade IV - patellar cartilage fibrillated with exposure of underlying bone in the tibia


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

  • 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

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Peer-reviewed papers

  • Quote:

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

    Citation: Slattery C, Kweon CY. Classifications in Brief: Outerbridge Classification of Chondral Lesions. Clin Orthop Relat Res. 2018 Oct;476(10):2101-2104. doi: 10.1007/s11999.0000000000000255. PMID: 29533246; PMCID: PMC6259817.

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Dr Sheila Strover (Editor)
BSc (Hons), MB BCh, MBA

See biography...