Pelvic Tilt Evaluation from Frontal Radiographs: The Validity, Inter-observer Reliability and Intra-observer Reproducibility of the Sacro-Femoral-Pubic Parameter

• Published in: The Journal of arthroplasty 2016
• Main Authors: Ragsdale, Mary, MD, Wong, Felix, MD, Boutin, Robert D., MD, Meehan, John P., MD
• Format: Article
• Language: English
• Subjects: Orthopedics
• ISSN: 0883-5403
• DOI: 10.1016/j.arth.2016.11.026

Abstract 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, inter-observer reliability and intra-observer repeatability of the SFP parameter in predicting the sagittal PT. Materials and Methods This is a retrospective study of 100 patients with frontal and lateral radiographs of the pelvis. Two observers independently measured the sacro-femoral-pubic angle on frontal x-ray, (midpoint of S1 endplate to centeroid of acetabula to upper midpoint of the pubic symphysis) and pelvic tilt (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 inter-observer reliability and intra-observer reproducibility were calculated using interclass correlation coefficient. Validity of the SFP parameter was calculated using Pearson's 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). Discussion 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.