Infant Hip Dysplasia Ultrasound: Graf Method Explained

Developmental dysplasia of the hip (DDH) is the most common musculoskeletal condition in newborns. Ultrasound is the standard imaging modality for hip evaluation in infants under 6 months (before the femoral head ossifies and becomes visible on X-ray). The Graf method is the most widely used technique worldwide.

Indications for Infant Hip Ultrasound

• Positive Barlow or Ortolani maneuver on physical exam
• Breech presentation at any gestational age
• Family history of DDH (first-degree relative)
• Female sex + breech presentation (highest risk)
• Clinical finding of hip click or asymmetric skin folds
• Screening programs (varies by institution and country)
• Follow-up after treatment (Pavlik harness)

Equipment

Probe: 5–12 MHz linear transducer. High frequency for small infants.

Patient position: Infant lies in the lateral decubitus position, hip being examined facing up, hip in neutral or 30–40° flexion.

Immobilization: A parent or assistant holds the infant steady. The baby is often easier to scan after feeding.

The Standard Coronal Plane (Graf Plane)

The Graf method requires a specific coronal image of the hip. Getting this plane right is everything — measurements made from the wrong plane are meaningless.

Landmarks for the Correct Plane

You need to see all three of these simultaneously:

1. Os ilium (iliac bone): Straight, horizontal echogenic line — this is the roof of the acetabulum. It must be perfectly flat (straight), not curved. A curved ilium means the probe is tilted.

2. Triradiate cartilage: The echogenic midpoint at the base of the acetabulum — the transition from the bony acetabular roof to the cartilaginous roof.

3. Labrum: The echogenic fibrocartilaginous rim at the outer edge of the acetabulum.

4. Femoral head: Round, hypoechoic structure sitting within the acetabulum.

If the ilium is not perfectly straight: Tilt the probe until it is. This is the most common technical error.

Graf Angle Measurements

Once you have the correct plane, draw three lines:

Baseline: Along the flat surface of the os ilium (the iliac wing). This is your reference line.

Bony roof line (alpha angle line): From the bony rim (the corner/edge of the bony acetabular roof) to the intersection with the baseline.

Cartilaginous roof line (beta angle line): From the labrum to the midpoint of the triradiate cartilage.

Alpha Angle (α)

The angle between the baseline and the bony roof line.

• Measures how much bony coverage the femoral head has
• Normal: ≥ 60°
• < 60°: Insufficient bony coverage — concerning for dysplasia

Beta Angle (β)

The angle between the baseline and the cartilaginous roof line.

• Measures the cartilaginous roof position
• Normal: < 55°

• 55°: Cartilaginous roof is displaced laterally

Graf Classification

Type	Alpha	Beta	Clinical Meaning
Type I	≥ 60°	< 55°	Mature, normal hip
Type IIa	50–59°	< 55°	Physiologically immature (< 3 months) — normal, monitor
Type IIb	50–59°	< 55°	Physiologically immature (> 3 months) — treatment warranted
Type IIc	43–49°	< 77°	Deficient bony roof, critical range
Type IId	43–49°	≥ 77°	Eccentric — cartilaginous roof displaced
Type III	< 43°	> 77°	Poor bony rim, cartilaginous roof pushed superiorly — subluxed
Type IV	< 43°	—	Inferiorly displaced cartilaginous roof — dislocated

Practical summary:

• Type I: Normal
• Type IIa: Normal if < 3 months — recheck at 3 months
• Type IIb+: Requires orthopedic consultation and often Pavlik harness
• Type III–IV: Dysplastic or dislocated hip — treatment necessary

Dynamic Assessment

In addition to the static Graf measurements, perform a dynamic stress test:

Technique: With the probe coronal, gently push the knee toward the table (posterior force on the hip). Observe whether the femoral head subluxes or dislocates out of the acetabulum.

• Stable: Femoral head stays in acetabulum
• Lax: Femoral head moves but returns
• Subluxable: Femoral head partially exits
• Dislocatable: Femoral head fully dislocates with stress

Document dynamic stability separate from the Graf type.

Common Technical Errors

Curved iliac line: The probe is tilted — the image plane isn't truly coronal. The ilium must be straight. Rotate or tilt the probe until it's flat.

Missing the triradiate cartilage: If you can't see the cartilage midpoint, you're too posterior or too anterior. Slide the probe to find it.

Too much pressure: Compress the hip and you'll push the femoral head into the acetabulum artificially — don't push hard with the probe.

Wrong side up: Always document which hip (right or left) is being imaged. The bony roof is always the deep (far) structure — ilium above, femoral head below.

Reporting Template

Document for each hip:

• Alpha angle (in degrees)
• Beta angle (in degrees)
• Graf type
• Femoral head coverage (% of femoral head covered by bony acetabulum)
• Dynamic stability
• Image quality / technical limitations

Reporting language:

• "Right hip: alpha 64°, beta 48°, Graf Type I. Femoral head well-seated within the acetabulum. No dynamic instability."
• "Left hip: alpha 52°, beta 53°, Graf Type IIa. Consistent with physiological immaturity given age of 6 weeks. Recommend clinical follow-up at 3 months."
• "Left hip: alpha 41°, beta 80°, Graf Type III. Poor bony acetabular coverage with superiorly displaced cartilaginous roof. Femoral head subluxes with posterior stress maneuver. Orthopedic consultation recommended."

Post-Harness Follow-Up

During Pavlik harness treatment, serial ultrasounds monitor hip development. Goals:

• Increasing alpha angle toward ≥ 60°
• Improved femoral head centering
• Reduction of dynamic instability

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SonoBuddy's Protocols section includes infant hip ultrasound. Measurements section covers Graf angle normal values by age.