Developmental dysplasia of the hip assistant

DDH (developmnental dysplasia of the hip) ultrasound assistant

Graf stage =

Anatomy

  1. Ilium
  2. Lower limb of ilium
  3. Triradiate cartilage
  4. Ligamentum teres
  5. Ischium
  6. Osteochondral junction
  7. Femoral metaphysis
  8. Greater trochanter
  9. Joint capsule
  10. Synovial fold
  11. Femoral head
  12. Labrum
  13. Cartilage of acetabulum
  14. Tendon of rectus femoris
  15. Gluteus minimus
  16. Gluteus maximus

Background

This calculator is an aid to the subdivisions of the Graf classification. The classification can be simplified to the following:

  • Graf I: normal hip (alpha >=60°), with (Ib) or without (Ia) a beta angle >55°
  • Graf IIa: immature hip (alpha 50-59°) less than 13 weeks of age, and at 6 weeks+ either maturing appropriately (+) or inappropriately (-) for age
  • Graf IIb: dysplastic hip, (alpha 50-59°) >13 weeks age
  • Graf IIc: severely dysplastic hip (alpha 43-49°, beta <77°)
  • Graf D: decentred hip (alpha 43-49°, beta >77°)
  • Graf III: dislocated hip (alpha <43°)
  • Graf IV: severely dislocated hip (alpha <43°)

The classification between type IIa+ and IIa- should not occur before 6 weeks. It is assumed here that the age in weeks is the last full week of age attained. Graf states that "to be on the safe side" it is assumed that development is linear with a minimum alpha angle as a neonate of 50, a minimum alpha angle as a 6 week old of 55, and by the end of the 12 th week an alpha angle of 60. This gives the following table:

AgeMinimum alpha angle
<150
<250.83333
<351.66667
<452.5
<553.33333
<654.16667
<755
<855.83333
<956.66667
<1057.5
<1158.33333
<1259.16667
<1360

Structures that must be visualised are, for the Graf method: (1) the lower limb of the os ilium, (2) the labrum, and (3) the horizontal section of the ilium indicating the standard plane. However, in a later chapter Graf also states that the osteochondral junction must be seen.

This page assumes the standard radiological convention of superior and rightwards structures are displayed on the left of the screen as opposed to Graf's method of flipping and rotating the images which, although representative of a standing baby, are not representative of how the baby is scanned.

A high frequency probe (e.g. 5-15 MHz) should be used, with the lower frequencies selected when greater penetration is needed.

Using the Graf method the hips should be slightly flexed [1, 2]. The patient should be on their side and the probe is placed, vertically orientated, on the lateral aspect of the hip.

After identifying the osteochondral junction, the femoral head, synovial fold, joint capsule, acetabular labrum, acetabular cartilage, bony part of the acetabulum and bony rim (see later) should be identified. The lower limb of the ilium and the triradiate cartilage indicate the acetabular center. The ilium should then be made straight on the screen. Since, at this point, the ilium raises anteriorly and superiorly and falls posteriorly and inferiorly, to get a straight image of the ilium, you need to align the probe between the rise and the fall.

If you are scanning the right hip, rotating the probe clockwise will result in the part of the image formed by the top of the probe to raise in a curve:

And if you rotate anticlockwise, it will cause it to fall as a curve:

So to make a straight line you either chase it down by rotating anticlockwise or raise it up by rotating clockwise whilst maintaining the centre of rotation such that the structures of interest remain on screen. The opposite rotation is needed when scanning the left hip.

To measure the angle, a baseline plane is drawn along horizontal ilium. A point is placed at the tip of the labrum and at the bony rim - the point where the Iliac bone turns from convexity to concavity along the lower limb. The angle between baseline and the line extending through the bony rim and to the deep tip of the lower limb of the os ilium is the alpha angle. The angle from the baseline to the line through the bony rim and the labrum is the beta angle.

References

  1. Hip sonography. Diagnosis and management of infant hip dysplasia. Second Edition. Graf R. Springer. 2006.