Pelvic Tilt Evaluation From Frontal Radiographs: The Validity, Interobserver Reliability and Intraobserver Reproducibility of the Sacro-Femoral-Pubic Parameter

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Background: The sacro-femoral-pubic (SFP) parameter, calculated using the SFP angle measured on a frontal pelvis radiograph, has previously been shown to have a strong correlation with sagittal pelvic tilt (PT) measured on a lateral x-ray. The purpose of this study is to assess the validity, interobserver reliability and intraobserver reproducibility of the SFP parameter in predicting the sagittal PT. Methods: This is a retrospective study of 100 patients with frontal and lateral radiographs of the pelvis. Two observers independently measured the SFP angle on frontal x-ray (midpoint of S1 end plate to centroid of acetabula to upper midpoint of the pubic symphysis) and PT on lateral x-ray (midpoint of sacral plate to the centroid of acetabula to vertical plane). The SFP parameter was defined using the equation: SFP parameter = 75 - SFP angle. The interobserver reliability and intraobserver reproducibility were calculated using interclass correlation coefficient (ICC). Validity of the SFP parameter was calculated using Pearson correlation coefficient. Results: The intraobserver reproducibility of the SFP parameter was excellent (ICC>0.90) for both observers. The interobserver reliability of all measurements was substantial for the SFP parameter (ICC>0.80) and PT (ICC>0.70). The concurrent validity of the SFP parameter was substantial (r = 0.70). Conclusion: Calculating PT from a frontal radiograph using the equation for the SFP parameter is a valid, reliable, and reproducible formula that may be used to predict sagittal PT.

Original languageEnglish (US)
JournalJournal of Arthroplasty
StateAccepted/In press - May 18 2016



  • Lewinnek safe zone
  • Pelvic tilt
  • Sacro-femoral-pubic angle
  • Sagittal plane alignment
  • Spine pelvic balance
  • Total hip arthroplasty dislocation

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine

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