The different hip types according to Graf [16]
| Graf-type | Age | Bony roof α angle | Bony rim | Cartilaginous roof β angle |
|---|---|---|---|---|
| I: mature hip | Every age | Good, α ≥ 60° | Angular/Blunt | Covering femoral head, β < 55° |
| IIa: physiological immature, age-appropriate | < 12 weeks | Sufficient, α = 50°–59° | Round | Covering femoral head |
| IIa+: physiological immature, age-appropriate | > 6 weeks | |||
| IIa-: physiological immature, maturation deficit | > 6 weeks | Inadequate, α = 50°–59° | ||
| IIb: delay in bony maturation | > 12 weeks | |||
| IIc: critical hip | Every age | Highly insufficient, α = 43°–49° | Round to flattened | Covering femoral head, stable, β < 77° |
| D: hip with beginning decentration | Displaced, β > 77° | |||
| III: decentred hip | Bad, α < 43° | Flattened | Pressed upwards | |
| IV: decentred hip | Pressed downwards |