Q: identify structures 1 to 9 ? show answer
Q: describe how the alpha angle described by graf is measured? show answer
Q: describe how the beta angle is measured as described by Graf? show answer
5 week old, second born girl, full term normal delivery. Selective screening programme for positive family history of DDH. USS of hip using a linear transducer and in a cradle (Sonofix) with probe guide system (Sonoguide)
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Anatomical checklist 1. chondrosseous border 2. Femoral head 3. Synovial fold 4. Joint capsule 5. Labrum 6. Hyaline cartilage acetabular roof 7. Bony roof 8. lower limb of os ilium 9. turning point ( bony rim, that is where the concavity turns to convexity)
Usability check 1. Lower limb - must be visible, 2. Plane of ilium - must be vertical (not anterior or posterior) 3. Labrum - must be visible
Alpha angle 60 degrees
Beta angle 78 degrees
Final Type Ib
The Graf ultrasound System of grading infant hips requires an image in the standard plane. obtained by a linear probe. The anatomical checklist 1 defines all anatomical structures that must be visible and identified before the image can be used for diagnostic purposes.
these are 1.chondrosseous border 2. Femoral head 3. Synovial fold 4. Joint capsule 5. Labrum (yellow dotted triangle) 6. Hyaline cartilage acetabular roof 7. Bony roof 8. lower limb of os ilium 9. turning point ( bony rim, that is where the concavity turns to convexity) By checking all named anatomical landmarks basic tilting errors are eliminated. If the checklist 1 is met only then proceed to Usability check list.
1. bright spot at Lower limb of os ilium - must be visible , 2. Plane of ilium - must be vertical ( not anterior or posterior) 3. Labrum - must be visible . Only once both check list criteria are met proceed to using 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. 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 as shown in figure 3.
The Beta angle measures the angle between the base line and the cartilage roof line which is the line from the turning point shown in figure 2 as a yellow dot above arrow 9 to the centre of the bright echo of the labrum 5 (yellow dotted triangle). 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 type1a hip and beta angle more than 55 makes it a type I b 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 impingement in adult life and extreme type 1b with small cartilage roofs may be prone to labral tears in adult life.
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