| Stage | Definition |
|---|---|
| 1 | Articular cartilage damage only |
| 2a | Cartilage injury with underlying fracture and surrounding bony edema |
| 2b | Stage 2a without surrounding bony edema |
| 3 | Detached but nondisplaced fragment |
| 4 | Detached and displaced fragment |
| 5 | Subchondral cyst formation |