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Pelvic rotation and tilt can cause misinterpretation of the acetabular index measured on radiographs.

van der Bom MJ, Groote ME, Vincken KL, Beek FJ, Bartels LW - Clin. Orthop. Relat. Res. (2011)

Bottom Line: The outcome of the measurement, however, depends on the orientation of the subject's pelvis relative to the xray source.Negative and positive error values can be interpreted as underestimations and overestimations of the acetabular index, respectively.Errors in acetabular index measurements were acceptable for R(rotation) values between 1.0 and 2.0 and R(tilt) values between 1.1 and 1.8.

View Article: PubMed Central - PubMed

Affiliation: Image Sciences Institute, Department of Radiology, University Medical Center Utrecht, Room Q0S.459, PO Box 85500, 3508 GA, Utrecht, The Netherlands. M.vanderBom@umcutrecht.nl

ABSTRACT

Background: Radiographic diagnosis and followup studies of developmental dysplasia of the hip are commonly performed by measuring the acetabular index on radiographs using Hilgenreiner's method. The outcome of the measurement, however, depends on the orientation of the subject's pelvis relative to the xray source. The influence of pelvic rotation and tilt on the measurement error has been evaluated separately but not in combination.

Questions/purposes: We asked whether (1) combinations of pelvic rotation and tilt introduced systematic error in acetabular index measurement in a reproducible way, and (2) ratios proposed to evaluate either pelvic rotation (R(rotation)) or pelvic tilt (R(tilt)) are influenced by pelvic tilt and rotation, respectively.

Methods: Radiographic measurements of the acetabular index, R(rotation), and R(tilt) were performed on digitally reconstructed radiographs of one high-resolution three-dimensional CT dataset with various combinations of pelvic rotation and tilt.

Results: For rotations and tilt up to 12°, the average systematic errors in the acetabular index varied from -8.8° to 4.5°. Negative and positive error values can be interpreted as underestimations and overestimations of the acetabular index, respectively. Errors in acetabular index measurements were acceptable for R(rotation) values between 1.0 and 2.0 and R(tilt) values between 1.1 and 1.8.

Conclusions: To limit the systematic error in assessing the acetabular index caused by pelvic misalignment, we recommend only radiographs acquired with ± 4° rotation and ± 4° tilt be considered acceptable.

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A graph shows the average rotation ratio as a function of pelvic rotation and constant values of pelvic tilt. Rotation ratio was calculated by the horizontal diameter of the largest obturator foramen divided by the horizontal diameter of the smallest obturator foramen.
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Fig6: A graph shows the average rotation ratio as a function of pelvic rotation and constant values of pelvic tilt. Rotation ratio was calculated by the horizontal diameter of the largest obturator foramen divided by the horizontal diameter of the smallest obturator foramen.

Mentions: The average rotation ratio () and average tilt ratio () were influenced by changes in pelvic tilt and rotation, respectively. Varying pelvic tilt from −12° to 12° and keeping pelvic rotation fixed at 0° resulted in ranging from 1.1 to 1.6 (Fig. 6) and even larger deviations of were observed for nonzero pelvic rotations. The variance of measured for 0° rotation and variable pelvic tilt most likely is caused by small asymmetries between the two obturator foramen. Similarly, ranged from 1.1 to 1.17 for a fixed pelvic tilt of 0° and pelvic rotation varying from −12° to 12° (Fig. 7).Fig. 6


Pelvic rotation and tilt can cause misinterpretation of the acetabular index measured on radiographs.

van der Bom MJ, Groote ME, Vincken KL, Beek FJ, Bartels LW - Clin. Orthop. Relat. Res. (2011)

A graph shows the average rotation ratio as a function of pelvic rotation and constant values of pelvic tilt. Rotation ratio was calculated by the horizontal diameter of the largest obturator foramen divided by the horizontal diameter of the smallest obturator foramen.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3094614&req=5

Fig6: A graph shows the average rotation ratio as a function of pelvic rotation and constant values of pelvic tilt. Rotation ratio was calculated by the horizontal diameter of the largest obturator foramen divided by the horizontal diameter of the smallest obturator foramen.
Mentions: The average rotation ratio () and average tilt ratio () were influenced by changes in pelvic tilt and rotation, respectively. Varying pelvic tilt from −12° to 12° and keeping pelvic rotation fixed at 0° resulted in ranging from 1.1 to 1.6 (Fig. 6) and even larger deviations of were observed for nonzero pelvic rotations. The variance of measured for 0° rotation and variable pelvic tilt most likely is caused by small asymmetries between the two obturator foramen. Similarly, ranged from 1.1 to 1.17 for a fixed pelvic tilt of 0° and pelvic rotation varying from −12° to 12° (Fig. 7).Fig. 6

Bottom Line: The outcome of the measurement, however, depends on the orientation of the subject's pelvis relative to the xray source.Negative and positive error values can be interpreted as underestimations and overestimations of the acetabular index, respectively.Errors in acetabular index measurements were acceptable for R(rotation) values between 1.0 and 2.0 and R(tilt) values between 1.1 and 1.8.

View Article: PubMed Central - PubMed

Affiliation: Image Sciences Institute, Department of Radiology, University Medical Center Utrecht, Room Q0S.459, PO Box 85500, 3508 GA, Utrecht, The Netherlands. M.vanderBom@umcutrecht.nl

ABSTRACT

Background: Radiographic diagnosis and followup studies of developmental dysplasia of the hip are commonly performed by measuring the acetabular index on radiographs using Hilgenreiner's method. The outcome of the measurement, however, depends on the orientation of the subject's pelvis relative to the xray source. The influence of pelvic rotation and tilt on the measurement error has been evaluated separately but not in combination.

Questions/purposes: We asked whether (1) combinations of pelvic rotation and tilt introduced systematic error in acetabular index measurement in a reproducible way, and (2) ratios proposed to evaluate either pelvic rotation (R(rotation)) or pelvic tilt (R(tilt)) are influenced by pelvic tilt and rotation, respectively.

Methods: Radiographic measurements of the acetabular index, R(rotation), and R(tilt) were performed on digitally reconstructed radiographs of one high-resolution three-dimensional CT dataset with various combinations of pelvic rotation and tilt.

Results: For rotations and tilt up to 12°, the average systematic errors in the acetabular index varied from -8.8° to 4.5°. Negative and positive error values can be interpreted as underestimations and overestimations of the acetabular index, respectively. Errors in acetabular index measurements were acceptable for R(rotation) values between 1.0 and 2.0 and R(tilt) values between 1.1 and 1.8.

Conclusions: To limit the systematic error in assessing the acetabular index caused by pelvic misalignment, we recommend only radiographs acquired with ± 4° rotation and ± 4° tilt be considered acceptable.

Show MeSH
Related in: MedlinePlus