Infant hip — Reference values: Ideal age and modality choice, Main indications, Standard coronal plane, Alpha angle — bony roof, Beta angle — cartilaginous roof/labrum.
Infant hip ultrasound depends strongly on age, technique, and local screening policy. In the United States, selective screening for risk factors or abnormal physical examination predominates; in some European countries universal screening is used. For international safety, this reference uses colors: green for mature stable hips, yellow for physiologic immaturity or divergent thresholds, and red for dysplasia, decentering, dislocation, persistent instability, or a technically inadequate examination.
| Measurement | Usual value | Note |
|---|---|---|
| Ideal age and modality choice | 6 weeks to 4 months is usually the most useful window | Before 6 weeks physiologic laxity increases false positives unless the physical examination is abnormal. When femoral head ossification limits visualization of the relationship with the triradiate cartilage, pelvic radiography becomes preferred.Source: ACR-AIUM-SPR-SRU Practice Parameter 2023 / ACR Appropriateness Criteria |
| Main indications | Abnormal or equivocal physical examination, breech presentation, family history, neuromuscular condition, or treatment follow-up | Oligohydramnios, intrauterine postural molding, asymmetric thigh creases, and leg-length discrepancy are relative indications.Source: ACR-AIUM-SPR-SRU Practice Parameter 2023 / AAOS |
| Standard coronal plane | Straight iliac line + labrum + ilium/triradiate cartilage transition | The plane is reliable only when it shows a straight ilium, the labral tip, and the transition from ilium to triradiate cartilage; the acetabulum should be shown at its deepest point.Source: ACR-AIUM-SPR-SRU Practice Parameter 2023 |
| Alpha angle — bony roof | Normal: >= 60° | It is the angle between the iliac baseline and the acetabular bony roof line. It measures bony roof depth/ossification and is the main angle for Graf classification.mature: ≥60°immature/age-dependent: 50–59° antes de 13 semanasdysplastic: <50° ou 50–59° após 13 semanasSource: Graf method / ACR-AIUM-SPR-SRU / International Hip Dysplasia Institute |
| Beta angle — cartilaginous roof/labrum | Helps separate Ia/Ib and IIc/D | It is the angle between the iliac baseline and the cartilaginous roof line, drawn from the acetabular bony rim to the labrum. Beta greater than 77° with alpha from 43° to 49° suggests decentering type D.Ia when alpha is normal: <55°Ib if alpha is normal: ≥55°type D if alpha 43–49°: >77°Source: Graf method / Radiology Assistant |
| Femoral head coverage | Practical consensus: >= 50% well covered | Some management criteria consider 45% or higher normal; therefore 45–49% is yellow. Less than 35% is dysplastic in appropriate-use criteria.consensus normal: ≥50%normal in some sources / borderline: 35–49%dysplastic: <35%Source: International Hip Dysplasia Institute / AAOS Appropriate Use Criteria / ACR references |
| Dynamic stability | Femoral head centered at rest and under gentle stress | In the transverse flexion view, assess ultrasound Barlow/Ortolani. More than 50% of the head should remain covered; below 45% suggests instability.Source: ACR-AIUM-SPR-SRU Practice Parameter / International Hip Dysplasia Institute |
| Green | Alpha >=60°, centered head, coverage >=50%, stable, and adequate standard plane. |
| Yellow | Alpha 50–59° before 13 weeks, coverage 35–49%, borderline beta, transient neonatal instability, or incomplete technique. |
| Red | Alpha <50°, alpha 50–59° after 13 weeks, coverage <35%, decentering/dislocation, persistent instability, or inadequate plane for conclusion. |
Source: Graf method / ACR-AIUM-SPR-SRU / AAOS AUC / IHDI
| Type | Criterion | Practical reading |
|---|---|---|
| I | Alpha >=60°. Ia if beta <55°; Ib if beta >=55°. | Mature hip; no imaging follow-up if clinical examination and context agree. |
| IIa | Alpha 50–59° before 13 weeks. | Physiologic immaturity. Follow local protocol; IIa− or worsening requires attention. |
| IIb | Alpha 50–59° at 13 weeks or older. | Dysplasia due to delayed maturation; coordinate with pediatric orthopedics according to protocol. |
| IIc | Alpha 43–49° and beta <=77°, head still centered. | Critical dysplasia even if centered; do not treat as simple immaturity. |
| D | Alpha 43–49° and beta >77° or signs of decentering. | Decentering hip; alert for treatment/referral. |
| III–IV | Alpha <43° with eccentric or dislocated head; labrum displaced or interposed. | Severe dislocation/subluxation. Priority communication. |
Source: Graf / Radiology Assistant / ACR Appropriateness Criteria
| Element | How to draw it | Common error |
|---|---|---|
| Iliac baseline | Straight line tangential to the lateral iliac cortex in the standard coronal plane. | Using an oblique image or curved ilium; this distorts alpha and beta. |
| Bony roof line | Line from the acetabular bony rim to the inferior bony roof point, forming the alpha angle with the iliac line. | Choosing the wrong rounded rim or measuring away from the deepest acetabulum. |
| Cartilaginous roof line | Line from the acetabular bony rim to the functional center/tip of the labrum, forming the beta angle. | Drawing from the bony roof instead of the bony rim; beta becomes artificial. |
| Inadequate plane | If the labrum, straight ilium, or triradiate cartilage is not shown, classification should be withheld. | Classifying despite no standard plane; this creates false normal or false dysplastic results. |
Source: ACR-AIUM-SPR-SRU Practice Parameter / Graf method
| Finding | Color | Interpretation |
|---|---|---|
| Coverage >=50% | Green | Well covered by the international practical rule. |
| Coverage 45–49% | Yellow | Normal in some management criteria, but below the classic 50% cutoff. |
| Coverage 35–44% | Yellow | Borderline range in appropriate-use criteria; integrate with alpha and stability. |
| Coverage <35% | Red | Dysplastic in AAOS appropriate-use criteria. |
| Subluxable, dislocatable, or dislocated | Red | Stability weighs as much as morphology; communicate and correlate with physical examination. |
Source: IHDI / AAOS AUC / ACR-AIUM-SPR-SRU
| Step | What to record | Color if absent |
|---|---|---|
| Both hips | Right and left, even when the concern is unilateral. | Red if only one side was assessed without justification. |
| Standard coronal neutral | Morphology, femoral head position, and alpha angle. | Red: do not assign Graf classification. |
| Transverse flexion view | Femoral head on the ischium, position at rest and with gentle stress. | Yellow/red according to clinical concern. |
| Dynamic maneuver | Ultrasound Barlow; Ortolani if the head is subluxated/dislocated to assess reducibility. | Yellow if omitted; acceptable to omit in Pavlik/splint. |
| Documentation | Side, orientation, age, whether stress was applied, alpha, beta/coverage when used, stability, and limitations. | Yellow if incomplete. |
Source: ACR-AIUM-SPR-SRU Practice Parameter 2023
| Situation | Risk | Practical action |
|---|---|---|
| Younger than 6 weeks | Physiologic laxity can mimic instability. | If physical examination is normal, follow local screening policy; if abnormal, scan and describe context. |
| Stable Graf IIa | Many mature spontaneously, but some are IIa− or have low coverage. | Do not call fully normal; recommend follow-up according to age/protocol. |
| Normal alpha with instability | Mature morphology does not exclude dynamic subluxability. | Report instability and correlate with orthopedics/physical examination. |
| Nonstandard plane | Can change alpha and beta by several degrees. | Repeat acquisition; if still limited, report as limited. |
| Using Pavlik harness or splint | Stress should not be routinely applied. | Document femoral head position in the device and omit stress. |
Source: ACR-AIUM-SPR-SRU / Radiology Assistant / Children’s Colorado