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

• Published in: The Journal of arthroplasty 2017-05, Vol.32 (5), p.1665-1669
• Main Authors: Ragsdale, Mary I., Wong, Felix S., Boutin, Robert D., Meehan, John P.
• Format: Article
• Language: English
• Subjects: Acetabulum; Adolescent; Adult; Aged; Aged, 80 and over; Arthroplasty, Replacement, Hip; Bone Plates; Female; Femur - diagnostic imaging; Humans; Lewinnek safe zone; Male; Middle Aged; Observer Variation; pelvic tilt; Pelvis - diagnostic imaging; Pubic Bone - diagnostic imaging; Radiography; Reproducibility of Results; Retrospective Studies; sacro-femoral-pubic angle; Sacrum - diagnostic imaging; sagittal plane alignment; spine pelvic balance; total hip arthroplasty dislocation; X-Rays; Young Adult
• ISSN: 0883-5403; 1532-8406
• DOI: 10.1016/j.arth.2016.11.026

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. 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. 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). 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.