First and second year — the floor first, then every step
Get the standard coronal plane first (straight iliac line, triradiate cartilage, labrum) — every Graf angle measured off-plane is wrong. Then measure the alpha angle and femoral head coverage, and stress for instability.
Orient first
Ultrasound is the test until the femoral head ossifies (roughly 4–6 months); after that, the radiograph takes over.
The Graf standard plane shows the iliac bone as a straight horizontal line, the lower limb of the ilium in the acetabular fossa, and the labrum.
Physiological immaturity (Graf IIa) before 12 weeks is common and usually resolves — the age in weeks is part of the classification.
Acquire the study
Linear probe, infant on the side with the hip slightly flexed; coronal standard plane, then transverse flexion views.
The manoeuvre
Confirm the standard coronal plane (straight iliac line, lower limb of the ilium, labrum) before any measurement.
Alpha angle in degrees (bony roof); normal is 60° or more (Graf I).
Beta angle in degrees (cartilaginous roof).
Femoral head coverage by the bony acetabulum on the coronal plane (commonly 50% or more is normal — verify).
Stress manoeuvre in the transverse plane: posterior displacement of the head (instability).
What confirms it
A Graf type with the infant's age, from a valid standard plane.
What licenses you to exclude it
Graf I (alpha ≥ 60°) on a valid plane with a stable hip.
The classic misread
Measuring on an oblique plane — the iliac line is not straight and the alpha angle is invalid.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Infant hip · Graf alpha angle (bony roof)60° or more
Coronal ultrasound of the infant hip in the standard Graf plane (straight iliac wing, labrum and lower limb of the os ilium all visible). The angle between the vertical cortex of the ilium and the bony acetabular roof.
An inadequate plane invalidates the angle entirely — confirm the three landmarks before reporting a number. Read with the beta angle. ⚠️ Do NOT confuse with the CAM-morphology alpha angle of the adult femoral head–neck junction, which is a different measurement with a different threshold.
USG
Infant hip · Graf beta angle (cartilaginous roof)under 55°
Same standard Graf coronal plane. The angle between the vertical cortex of the ilium and the triangular labral fibrocartilage.
Only useful in combination with the alpha angle; reported alone it is not interpretable.
USG
Diagnostic criteria
Infant hip (Graf types) · Graf type as the report word — technique required
a named Graf I–IV type from the already-registered alpha (and beta) angles; type, not a remembered “normal hip millimetre”, is the sentence
Standard Graf coronal plane: iliac wing straight, bony roof, labrum and femoral head on one image; alpha is the angle between the iliac baseline and the bony acetabular roof — the same technique as the already-registered Graf-alpha entry.
A non-standard plane invents dysplasia. Do not invent an age-as-fact cut-off.
USG · paediatric
Infant hip (coverage) · Femoral-head coverage on ultrasound, companion to Graf
femoral-head coverage percentage and the Graf alpha/beta angles (already registered) are a SET; published coverage floors exist and should be read from the local hip-screening protocol
Graf type, coverage percentage and the clinical Ortolani/Barlow are different tests. Do not invent a coverage percentage and then treat it as a Graf angle.
USG · X-ray · paediatric
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.