Overview
The head is covered with a stocking
cap made of a piece of stocking with a knot in one end. This allows the hair to
lie flat and a yellow sticker with the infant's ID written on it is attached to
the stocking cap. A yellow cape is placed around the shoulders to mask out competing
colours in the clothing or environment. Then a head band is placed around the largest
occipitofrontal circumference.
We use a stretchy neoprene headband covered in blue fabric, with sliding green markers
to indicate the anterior ear attachments and a red nose marker of known length (50mm),
to indicate the midline of the nose. These markers are positioned directly above
the landmarks, assisted by small pointers extending below each marker.
We then take a series of digital photographs from above the head, while the child
sits on the mother's knee or plays with toys on the floor. The camera has a swivelling
LCD screen to enable this to be done. The distance is 60 to 80 cm from the vertex
of the head. Ideally, three "good" photos need to be obtained, although with infants
moving constantly this is not always possible.
The programme calculates the mean measurements of the three photos. Each photo needs
to have as much of the blue band showing as possible. If the head is tilted, the
band will be narrower on one side and the results are not as accurate. Occasionally,
there will be prominent parietal eminences that will obscure part of the band, but
the computer programme can correct for this. When the computer programme "reads"
the photos, it effectively does the following:
- A line is drawn between the ear markers (the green line in the diagram).
- The midpoint of this line effectively becomes the head centre.
- From the head centre, a line is drawn to the centre of the red nose marker.
- This becomes the midline of the head, and is extended to the posterior of the head.
(We rely on the fact that there is minimal deviation of the midline in deformational
plagiocephaly, as shown in several papers in the literature).
- The head width is calculated by finding the maximum width perpendicular to the midline.
Head length and head width are the white lines in the diagram.
- Cephalic index (CI) is calculated: (width / length) * 100. We use 93% as our cutoff
between normal and abnormal.
- The computer programme calculates pseudo frontozygomatic points on either side of
front midline, from data correlating normal head circumference vs age and outer
canthal distance vs age, plus 5mm. In reality, the range of distances between FZ
and FZ is of the order of 7.2 cm to 7.8 cm. In one large data set of infants of
various ages, the mean was 7.4 cm.
- From each FZ, the computer programme then draws a line to a point that is 40 degrees
either side of the midline at the back of the head. These are the yellow lines in
the diagram and are the oblique cranial lengths.
- From these, the ratio of the longest length to the shortest is calculated (times
100), and this becomes the oblique cranial length ratio, or OCLR.
- We have determined "normal" to be less than 106%.
Download HeadsUp operational definitions(104.4KB PDF)
Download the HeadUp programme(1.9MB ZIP)
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