We investigated the relationship between pelvic incidence (PI) with anterior pelvic plane angle (APPA), pelvic tilt (PT) angle, and sacral slope (SS) in standing and sitting positions to identify the best parameter expressing the pelvic functional orientation in the sagittal plane.
We enrolled 109 consecutive patients (M:F = 43:66) eligible for a primary total hip arthroplasty (THA) with an average age of 63.4 years (15-85). EOS 2D/3D radiography was performed in standing and sitting positions before THA to evaluate the functional pelvic orientation. 3D images took into account the patient-specific sagittal balance measuring APPA, PT, SS, and PI.
In standing position, functional parameters measured 5° ± 7.1 for APPA, 11° ± 8.3 for PT, 43° ± 8.5 for SS, and 53° ± 10.9 for PI. In sitting position, they were −18° ± 10.4 for APPA, 34° ± 11.8 for PT, 20° ± 12.6 for SS, and 54° ± 10.9 for PI. There was no significant difference between men and women in terms of the functional parameters in both positions. No relationship was found between APPA and PI in both positions. SS correlated with PI in standing (r = 0.66; P < .0001; R2 = 0.44) and sitting (r = 0.51; P < .0001; R2 = 0.26). PT correlated with PI in standing (r = 0.65; P < .0001; R2 = 0.42) and sitting (r = 0.38; P < .0001; R2 = 0.14).
SS shows the highest correlation with functional pelvic tilt. The study suggests that adjustments in acetabular anteversion during primary THA should be based on SS.