Can measurements from an anteroposterior radiograph predict pelvic sagittal inclination?

Abstract

Pelvic sagittal inclination (PSI) is often evaluated in patients with hip pathology using lateral radiographs. However, it would be useful if PSI could be predicted from an anteroposterior radiograph since this film is ubiquitous in the evaluation of hip pathology. Herein, computer‐modeling was applied to predict PSI from radiographic measurements assessed in the anteroposterior plane. Three‐dimensional surface models of the pelvis, femur, and sacrum were reconstructed from computed tomography images of 50 women with hip dysplasia. This study cohort was selected as changes in PSI alter femoral head coverage, which is relevant to the diagnosis and treatment of hip dysplasia, a known cause of hip osteoarthritis. Five radiographic parameters commonly used to independently estimate PSI were evaluated after bone surfaces were projected to an anteroposterior plane, including the symphysis to sacrococcygeal joint distance (S‐S distance), the pelvic foramen aspect ratio (PF ratio), the distance between the symphysis and a line connecting the femoral head centers (S‐H distance), the sacro‐femoral‐pubic angle (SFP angle), and the pelvic vertical ratio (PVR). Regression models determined the ability of these parameters to predict PSI from −20° to 20° at 1° increment. All five parameters showed a strong correlation with the PSI (all r > 0.9). From the regression models, PSI was estimated with a median (maximum) absolute error of 3.6° (18.4°), 3.8° (17.7°), 5.2° (17.9°), 5.8° (28.8°), and 3.2° (23.5°) for the S‐S distance, PF ratio, S‐H distance, SFP angle, and PVR, respectively. The regression model for S‐S distance had a mean slope of 2.18 that ranged from 1.98 to 2.41 when the sacrococcygeal joint was located superior to the symphysis. Results indicated that substantial errors occur when estimating the actual value of PSI from an anteroposterior radiograph. However, the change in PSI could be estimated from the S‐S distance, which may aid surgeons to successfully increase head coverage through periacetabular osteotomy and to locate the acetabular cup in a functional position for total hip arthroplasty.

The accuracy in determining pelvic tilt from anteroposterior pelvic radiographs in patients awaiting hip arthroplasty

“…Tamura et al 32 also reported differences in orientation of the pelvis between supine and standing differences. Further, PT is known to change between standing and supine positions, although the difference is highly correlated ( r = .82) 33 . It is possible these observations may explain some of the differences we found in our results when compared to prior reports.…”

Change of Pelvic Sagittal Tilt after Total Hip Arthroplasty in Patients with Bilateral Crowe Type IV Developmental Dysplasia of the Hip

“…Tannast et al 26 . and Uemura et al 35 . showed that only the SSc distance had a moderately strong positive correlation with PST, which could be found for all patients based on a large group.…”

“…In addition, AP pelvic radiographs remain the standard of care imaging modality for pre and postoperative assessment during THA owing to easy accessibility, cost effectiveness, low radiation exposure, and widespread availability, 18,26,33,36 and the use of AP radiographs to assess changes in pelvis has been validated, 34,37 which proved that the position and radiographic methods we used in this study was appropriate. And radiographic overlap could occur in a lateral position between right and left hips, making the diagnostic evaluation complicated and less efficient 18,35,38 …”

“…And radiographic overlap could occur in a lateral position between right and left hips, making the diagnostic evaluation complicated and less efficient. 18,35,38 Comparison of Parameters for Evaluating PST In this study, we followed the method of Tannast et al 26 to evaluate the change in PST by the measurements of pelvic landmarks and the obturator foramina. Tannast et al compared six methods on plain AP radiographs and revealed that the H/W ratio of the obturator foramina was one of the parameters having a significantly strong correlation with PST in both males and females.…”

Proposal of accurate cup placement procedure during total hip arthroplasty based on pelvic tilt discrepancies in the lateral position

“…Our study had some limitations. Because it is generally believed that it is difficult to measure sagittal or axial pelvic tilt from the anteroposterior view of the pelvis 19 , concerns remain about the measurement error on TPP images. In fact, it is almost impossible to accurately measure axial pelvic tilt from the anteroposterior view of the pelvis.…”