Ultrasound Diagnostics and Graf Angles
Ultrasound is a key method for evaluating the developing hip joint. Normally, the femoral head is centered and adequately covered by the acetabulum, and the onset of ossification is visualized.
For objective assessment, Graf angles are used:
- Alpha ($\alpha$) angle reflects the degree of development of the bony roof.
- Beta ($\beta$) angle characterizes the cartilaginous roof.
Depending on the values of these angles, the state of the bony and cartilaginous roofs, joints are classified into types (I–IV). For example, Type I is a mature joint ($\alpha$ angle > 60°), while Types III and IV correspond to dislocation, where the bony roof is poor and the cartilaginous roof is displaced or interposed.
Radiographic Signs: Putti's Triad
On an anteroposterior pelvic radiograph, several reference lines are evaluated to diagnose dysplasia:
- Hilgenreiner's line — a horizontal line passing through the triradiate cartilage.
- Perkin's line — a vertical line dropped from the lateral margin of the acetabular roof.
- Shenton's line — an arc-like line formed by the inferior border of the superior pubic ramus and the inferomedial border of the femoral neck (disrupted in dysplasia).
Classic Putti's triad includes three signs:
- Increase in the acetabular angle (the angle between Hilgenreiner's line and a line tangential to the acetabular roof).
- Delayed ossification or small size of the femoral head ossification center.
- Superolateral displacement of the proximal femur (above Hilgenreiner's line and lateral to Perkin's line).
Related Hip Pathologies
In addition to dysplasia, pediatric and adolescent practice encounters other hip disorders that require diagnostic imaging.
Legg-Calvé-Perthes disease (idiopathic avascular necrosis):
- Early sign: "crescent sign" (radiolucent subchondral fracture).
- Progression: fragmentation, sclerosis, formation of coxa magna deformity.
- MRI is frequently used to assess tissue viability.
Slipped capital femoral epiphysis (SCFE):
- Most commonly occurs in adolescents during the pubertal growth spurt.
- The metaphysis displaces anterosuperiorly relative to the epiphysis.
- The "frog-leg" lateral projection is mandatory for diagnosis, on which Klein's line and the slip angle are evaluated.
Putti's triad: Increased angle, Delayed ossification, Superior displacement (Superolateral displacement).
Class and exam questions
Why are Graf angles measured?
Graf alpha and beta angles are measured on ultrasound to classify the degree of acetabular development and evaluate femoral head cartilage coverage.
What happens to Shenton's line in dislocation?
In hip dislocation or subluxation, the smooth arc-like Shenton's line becomes disrupted.
In which projection is slipped capital femoral epiphysis best visualized?
Frog-leg lateral radiography is the most sensitive projection for detecting SCFE.
What else to study on this topic
- Detailed analysis of the Graf ultrasound classification (types IIa–IId)
- Computed tomography (CT) with 3D reconstruction for postoperative monitoring
- Classifications of Legg-Calvé-Perthes disease (Herring and Catterall)
- Risk factors and epidemiology of slipped capital femoral epiphysis (SCFE)
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