Normal pediatric hip ultrasound - Graf type I

Case Discussion

The Graf ultrasound system of grading infant hips requires an image in the standard plane. obtained by a linear probe. 

The anatomical checklist (see annotated image) defines all anatomical structures that must be visible and identified before the image can be used for diagnostic purposes. By checking all named anatomical landmarks basic tilting errors are eliminated. If the anatomical checklist 1 is met only then proceed to the usability checklist:

1. Lower limb - must be visible.
2. Plane of ilium - must be vertical (not anterior or posterior).
3. Labrum - must be visible.

Only once both checklist criteria are met proceed to use the image for diagnosis and typing. One exception to this rule is a decentred hip.

The alpha angle measures the bony roof coverage and the beta angle measures the cartilage roof coverage. For the alpha angle - first, draw the base line which is the vertical line parallel to either the outer cortex or inner cortex of the ilium. next choose the lowest and lateral most point of the bright spot of the lower limb of the os ilium shown as the yellow dot above marker 8 and using that point draw a line that just tangentially touches bone. This line must not cut the white echo of the ilium but just touch it.

The beta angle measures the angle between the base line and the cartilage roof line, which is the line from the turning point to the center of the bright echo of the labrum 5. The three lines in the vast majority of cases do not cross at a single point except in a mature type 1 hip with a sharp bony corner.

Type 1 hip has an alpha angle of more than 60 degrees. In a type 1 hip, a beta angle less than 55 makes it a type 1a hip and beta angle more than 55 makes it a type Ib hip.

In clinical practice, type Ia and 1b hip are both normal hips, there is, however, a hypothesis that extreme type 1a hips with larger cartilage cover may be prone to pincer femoroacetabular impingement in adult life and extreme type 1b with small cartilage roofs may be prone to labral tears in adult life.