In order to assess hip disorders in children and adults, clinical parameters are measured on frontal X-rays of the pelvis [1Brurås. 2011.

Cliquez ici pour aller à la section Références, 2Anderson. 2011.

Cliquez ici pour aller à la section Références]. These radiographs require standard positioning of the patient during acquisition. The aim of this study was to estimate the effect of erroneous positioning of children and adults, during pelvis frontal X-ray acquisition, on the reliability and validity of hip parameters.

Helical pelvis CT scans (slice thickness - 0.6mm) of 8 children (3 F and 5 M, age - mean 12 - SD 2.2) and 9 adults (5 F and 4 M, age- mean 51 - SD 26) were considered. Frontal digitally reconstructed radiographs (FDRRs) were reconstructed from CTs. Then, for each patient, axial rotation (AR) of the pelvis was simulated and the corresponding FDRRs were reconstructed at 5°, 10°, 15° and 20° of AR. Clinical parameters were measured digitally on each radiograph, for both the left and right sides of each patient - vertical center edge (VCE) angle, HTE angle, sharp's angle, lateral subluxation (LatSub) angle, ACETABULAR FOssa relative to the ilioischial line (AcetFossa), acetabular depth (AcetD) distance and acetabular width (AcetW) distance. Three trained operators repeated the measurements 3 times each, in each AR position. Intraclass Correlation Coefficient (ICC) was evaluated for intra- and inter-observer agreement. The 95% confidence interval (95% CI) was calculated as 2SDs of inter-observer reliability. Bias of each clinical parameter, in each AR position, was calculated as the absolute mean difference relatively to the 0° position.

Intra- and inter-observer agreement was shown to be very high (ICC>0.9) for all parameters and all AR positions except for the AcetFossa (ICC=0.5) in adults. In the absence of AR of pelvises (0/730+), 95% CI of HTE, VCE, Sharp's angle were lower than 5° and lower than 1cm for the AcetabD, AcetW, AcetFossa and LatSub. Ninety-five percent CI increased with pelvic AR - >5° for VCE and reached 7/730+ for HTE at 20/730+ of AR. However, it remained constant for the remaining parameters. All the parameters showed an increase in bias during AR of the pelvis, where VCE showed greatest bias (6° in children and 4.6° in adults) at 20° position. AcetabD, AcetW, AcetFossa and LatSub exhibited a bias<1cm.

Hip parameters measured on frontal radiographs were shown to be less accurate and less reliable when pelvic AR increased. The bias was systematically higher for all parameters in all AR positions in children compared to adults. It exceeded 10% of normative values for most of the clinical parameters in both children and adults, when AR exceeded 10°.