Graf's Ultrasound of Neonatal Hip Joints: Positioning, α/β Angles, and Types I–IV
Positioning and Standard Section
The assessment is performed on a longitudinal coronal section, which should include the bony roof of the acetabulum, the cartilaginous roof, the labrum, the triradiate (Y-shaped) cartilage, the ischium, and the ossified metaphysis of the femur. This standard view allows for the correct measurement of the α and β angles. In the transverse plane, the centering of the femoral head in the acetabulum is determined (ice cream cone view), where the anterior column of the acetabulum, the labrum, the femoral metaphysis, and the gluteal muscle are visualized.
Angles α and β
The image should include the femoral head, acetabulum, labrum, and ilium at the transition to the triradiate cartilage — this ensures the correct measurement of Graf's angles. These angles quantitatively assess the joint.
- Angle α (bony roof) — normally > 60°.
- Angle β (cartilaginous roof) — usually < 55°.
The β angle is less critical than the α angle.
Modified Graf Staging (Types I–IV)
| Type | Characteristic | α | β |
|---|---|---|---|
| Ia | Mature joint, angular (sharp) bony prominence | > 60° | < 55° |
| Ib | Mature joint, rounded bony prominence | > 60° | < 55° |
| IIa | Physiological immaturity < 3 months | 50–59° | 55–77° |
| IIb | Delayed ossification, immaturity > 3 months | 50–59° | 55–77° |
| III | [specify: data not provided in the source] | [specify] | [specify] |
| IV | [specify: data not provided in the source] | [specify] | [specify] |
Interpretation of Dysplasia (DDH)
Developmental dysplasia of the hip (DDH; synonym — congenital dysplasia of the hip, a less accurate term) is defined as underdevelopment of the acetabular component of the hip joint. In addition to static assessment, dynamic sonography of the infant hip is applied. In the posterior lip view, the triradiate cartilage is normally visualized between the ilium and ischium; deviations help distinguish a normal joint from a dislocated one.
Frequently asked questions
What are the normal values for angles α and β?
Normally, angle α > 60°, angle β is usually < 55°.
What structures should be on the standard coronal section?
The femoral head, bony and cartilaginous roof of the acetabulum, labrum, triradiate cartilage, ischium, and ossified femoral metaphysis.
How does type IIa differ from IIb according to Graf?
IIa — physiological immaturity < 3 months; IIb — delayed ossification, immaturity > 3 months. Both have α = 50–59°, β = 55–77°.
Which angle is more important for assessment?
The β angle is less critical than the α angle.
What does the transverse view show?
The centering of the femoral head in the acetabulum — ice cream cone view.