Graf Alpha angle - measured between baseline and the bony roofline
Graf Beta angle - measured between baseline and the cartilage roofline
Case Discussion
The 3 lines used to draw the Alpha and Beta angles have individual definitions, The lines are independent of each other. In 99% of cases, they do not cross at one point.
The Base Line is drawn from the point where the perichondrium meets the ilium (Fig 1 iii), from this pivot point draw a vertical line down tangential to the surface of the ilium.
The Bony roofline is drawn from the lower limb of the os ilium (Fig1 i), from this pivot point the line is drawn superolateral tangential to the bony roof.
The cartilage roofline is drawn from the turning point (represented by a sound shadow, where the concavity of the acetabulum first turns to a convexity ) to the center of the echogenic labrum. When the sound shadow is wide use the lateral most point of the sound shadow to draw the line.
The descriptions in the Graf system are based on the image being an AP projection of the right hip
Most errors in diagnosis and angle measurements occur due to incorrect anatomical identification of structures on the ultrasound image.