Errors in measurement of acetabular index.
Errors in determining the acetabular index can be induced either by incorrectly positioning the child for radiographs or by inter- or intraobserver errors. From postmortem radiographic studies, we have determined the magnitude of these errors. The error caused by pelvic rotation is +/- 3 degrees if the obturator foramina ratio is kept within 0.5 to 2. If pelvic flexion/extension is confined to +/- 10 degrees, the error induced by flexion/extension is +/- 3 degrees. The intraobserver error was +/- 2 degrees, and the interobserver error was +/- 3 degrees. Under these circumstances, the total error is +/- 5 degrees. We have not been able to find a satisfactory way of limiting the flexion/extension to +/- 10 degrees. In some circumstances, particularly if a child is distressed, the flexion/extension may be 20 degrees from neutral; under these circumstances, errors as large as 10 degrees can occur. Surgeons should be aware that very large errors can occur when the acetabular index is measured.
Ospedale San Raffaele, Milan, Italy.
N M
NM
Portinaro
D W
DW
Murray
T P
TP
Bhullar
M K
MK
Benson
D000077:Acetabulum / Q000033:anatomy & histology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009068:Movement / Q000502:physiology; D015588:Observer Variation; D010384:Pelvic Bones / Q000502:physiology