Catterall groups
The severity and spread of Perthes disease are classified as follows:
| Stage | Description |
| I | Anterolateral (“front and side”) involvement without sequestrum (dead piece of bone), metaphyseal involvement (metaphysis: section of long bones that lies between the bone shaft (diaphysis) and the epiphysis), and subchondral (articular bone on which cartilage rests) fracture (broken bone) |
| II | Anterolateral sequestrum, metaphyseal reaction, and subchondral fracture in anterior half |
| III | Large sequestrum, sclerotic demarcation to vital portions, subchondral fracture line also in posterior half of epiphysis (end of bone) |
| IV | Entire femoral head involved, dorsal signs of remodeling (interaction of osteoblasts/bone-building cells and osteoclasts/bone-degrading cells) |
Classification according to lateral epiphyseal height according to Herring.
| Stage | Description |
| Herring A | Lateral column of epiphysis not reduced in height |
| Herring B | lateral column of epiphysis <50% reduced in height |
| Herring C | Lateral column of epiphysis >50% reduced in height |
Classification according to x-ray morphology (according to Waldenström).
| Stage | Description |
| Initial stage | Edema formation (fluid accumulation) in the bone and accompanying inflammation of the joint capsule |
| Condensation stage | Condensation of the affected bone |
| Fragmentation stage | Collapse of the femoral head or parts of the head |
| Reparation stage | Reconstruction of the femoral head or to heal in a deformed position |
