Pelvic inclination and spatial orientation of the acetabulum. A radiographic, computed tomographic and clinical investigation.

In a study of 40 young adults the pelvic inclination measured by a specially constructed inclinometer was found to be the same in the supine and standing positions when related to the horizontal and frontal planes, respectively. Consequently supine CT measurements of the hip are also representative of corresponding standing angles. The variations of the acetabular anterversion and the sector angles on CT of the hips in 5 adult corpses were measured by angulating the gantry in increments of 5 degrees to +/- 20 degrees. An approximate linear relationship was found for all parameters, the acetabular anteversion varied 0.5 degree with 1 degree pelvic rotation, and the sector angles 0.7 degree. A theoretic mathematical model for the variation of the acetabular anteversion outside the measured range employing a sine curve is introduced.