Assessment of the acetabular version in relation to sagittal sacropelvic parameters

The relationship between acetabular orientation and the sacropelvic parameters is of interest to both hip and spine surgeons as it is increasingly clear disease in one area can affect the other, including the outcome of surgical procedures. The aim of this study was to further clarify the relationship between measures of acetabular orientation and sacropelvic parameters. This study utilized a trauma CT database. A total of 100 scans on adult patients without overt hip or spinal disease were included. Measures of acetabular orientation included the acetabular sagittal angle (ASA) which uses the anterior pelvic plane as a reference and sacroacetabular angle which uses the sacral endplate as a reference (SA); spinopelvic parameters include the pelvic incidence (PI), sacral anatomic orientation (SAO) and pelvic thickness (PTH). Mean age 48.2 years (SD 18.0), 62% male. Mean values were: PI 50.5, SAO 50.7, PTH 106.4 mm, ASA-right 62.1, ASA-left 64.0, SA-right 67.2, and SA-left 65.4. There was substantial correlation between PI and SA (r = 0.628-0.630) and also between SAO and SA (-0.657 to -0.692). Liner regression determined SA was best predicted by the model: SA = 81 × SAO + 0.36 × PI. When using the anterior pelvic plane as a reference to define acetabular orientation, there does not appear to be any significant relationship between the sagittal orientation of the acetabulum and sacropelvic parameters. Using the sacrum as a common point of reference allows some further understanding of the interplay between pelvic parameters and the orientation of the acetabulum.