Williams et al used the annual progression ratio (APR) to describe progression of early-onset scoliosis. The authors are from multiple children's hospitals in the United States and Hacettepe University in Turkey.
Patient selection: scoliosis
Parameters:
(1) major curve in degrees at time 1
(2) major curve in degrees at time 2
(3) number of months or days between the 2 curve measurements
APR in degrees per year =
= ((major curve at time 2) - (major curve at time 1)) / (12 / (number of months between measurements)) =
= ((major curve at time 2) - (major curve at time 1)) / (365 / (number of days between measurements))
wherer:
• The time frame in the paper was months. The use of days was added..
• In the paper the number of months between measurements was around 6 months. An interval longer than a year would be less sensitive to rapid changes in the curvature.
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