Assessment of pelvic tilt in anteroposterior radiographs by means of tilt ratios
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In anteposterior (AP) radiographs, cup position in total hip arthroplasty and acetabular anatomy in hip-preserving surgery are highly influenced by pelvic tilt. The sagittal rotation of the anterior pelvic plane is an important measurement of pelvic tilt during hip surgery. Thus, correct evaluation of cup position and acetabular parameters requires the assessment of pelvic tilt in AP radiographs.
Changes in pelvic tilt inversely change the height of the lesser pelvis and the obturator foramen in AP radiographs. Tilt ratios were calculated by means of these two parameters in simulated radiographs for ten male and ten female pelvises in defined tilt positions. A tilt formula obtained by exponential regression analysis was evaluated by two blinded investigators by means of 14 simulated AP radiographs of the pelvis with pelvic tilts ranging from + 15° to − 15°.
No differences were found between male and female tilt ratios for each 5° step of simulated pelvic tilt. Pelvic tilt and tilt ratios correlated exponentially. Using the tilt formula, the two blinded investigators were able to assess pelvic tilt with high conformity, a mean relative error of + 0.4° (SD ± 4.6°), and a mean absolute error of 3.9° (SD ± 2.3°). Neutral pelvic tilt is indicated by a tilt ratio of 0.5 when the height of the lesser pelvis is twice the height of the obturator foramen.
The analysis and interpretation of cup position and acetabular parameters may be improved by our method for assessing pelvic tilt in AP radiographs.
KeywordsPelvic tilt Cup position Anterior pelvic plane Total hip arthroplasty Acetabular parameters
There is no funding source.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This study is a retrospective analysis of data obtained in a registered, prospective, controlled trial (DRKS00000739, German Clinical Trials Register). This investigation was approved by the local Ethics Committee (No. 10-121-0263). All procedures were in accordance with the ethical standards of the responsible committee on human experimentation and with the Declaration of Helsinki of 1975, as revised in 2000. The study collective including 3D CT of all patients was anonymized using numbers.
Informed consent was obtained from all individual participants included in the study.
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