Roles of Sagittal Anatomical Parameters of the Pelvis in Primary Total Hip Replacement for Patients with Ankylosing Spondylitis.

We examined the correlation between acetabular prostheses and sagittal anatomical parameters of the pelvis for the preoperative evaluation of total hip arthroplasty in 29 patients with ankylosing spondylitis between April 2004 and November 2011. No implant dislocation or subsidence was observed at 4.18 years. The relationship between sagittal parameters conformed to the equation Pelvic incidence (PI)=Pelvic tilt (PT)+Sacral slope (SS). Better outcomes were achieved in the SS>PT group, postoperative function was positively correlated with SS/PI. Functional abduction and anteversion were positively correlated with PT but negatively correlated with SS. Due to the compensatory changes in the pelvis and spine of patients with AS, the preoperative assessment of sagittal parameters plays pivotal roles in placing acetabular prostheses in optimal positions and preventing postoperative impingement and dislocation.