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Table 1 The Graf classification system of developmental dysplasia of the hip, based on sonographic angles of the hip

From: Tübingen hip flexion splints for developmental dysplasia of the hip in infants aged 0–6 months

Type

Description

Bony Roof

Bony Rim

Cartilage Roof

α-angle

β-angle

I

Mature hip

Good

Angular/blunt

Covers the femoral head

≥60

< 77

IIa

Physiological (< 3 month)

Deficient

Rounded

Covers the femoral head

50–59

> 55

IIb

Delay of ossification (> 3 month)

Deficient

Rounded

Covers the femoral head

50–59

< 55

IIc

Critical hip

Severely deficient

Rounded to flattened

Still covers the femoral head

43–49

< 77

D

Decentering hip

Severely deficient

Rounded to flattened

Displaced

43–49

> 77

III

Dislocated hip

Poor

Flattened

Pressed upward, perichondrium slopes cranially

< 43

> 77

IV

Dislocated hip

Poor

Flattened

Pressed downward, perichondrium is horizontal or dips caudally

< 43