Restricted spinopelvic mobility received attention as a contributing factor for total hip arthroplasty (THA) instability. However, it is still unknown, how the spinopelvic function is influenced by age. In identifying the patients at highest risk for altered spinopelvic mechanics the study aimed to determine the association of age on the individual segments of the spinopelvic complex and global spinal sagittal alignment in patients undergoing THA. 197 patients were included in the prospective observational study conducting biplanar stereoradiography (EOS) in standing and sitting position pre-and postoperatively. Two independent investigators assessed C7-sagittal vertical axis (C7-SVA), cervical lordosis (CL), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), anterior plane pelvic tilt (APPT), and pelvic femoral angle (PFA). Key segments of the spinopelvic complex are defined as lumbar flexibility (Delta LL=LLstanding-LLsitting), pelvic mobility (Delta Delta SS=SSstanding-SSsitting) and hip motion (Delta PFA=PFA(standing)-PFA(sitting)). Pelvic mobility was further defined based on Delta SS=SSstanding-SSsitting as stiff (Delta SS<10 degrees), normal (Delta SS >= 10 degrees-30 degrees) and hypermobile (Delta SS>30 degrees). The patient collective was classified into three groups: (1)<60 years (n=56), (2)>= 60-79 years (n=112) and (3)>= 80 years (n=29). Lumbar flexibility (Delta Delta LL) was decreased with increasing age between all groups (36.1 degrees vs. 23.1 degrees vs. 17.2 degrees/p(1+2)<0.000, p(2+3)=0.020, p(1+3)<0.000) postoperatively. Pelvic mobility ( SS) was decreased in the groups 2 and 3 compared to group 1 (21.0 degrees and 17.9 degrees vs. 27.8 degrees/p(1+2)<0.000, p(2+3)=0.371, p(1+3)=0.001). Pelvic retroversion in standing position (APPT) was higher in group 2 and 3 compared to group 1 (1.9 degrees and-0.5 degrees vs 6.9 degrees/p(1+2)<0.000, p(2+3)=0.330, p(1+3)<0.000). Global sagittal spinal balance (C7-SVA) showed more imbalance in groups 2 and 3 compared to group 1 (60.4 mm and 71.2 mm vs. 34.5 mm/p(1+2)<0.000, p(2+3)=0.376, p(1+3)<0.000) postoperatively. The preoperative proportion of patients with stiff pelvic mobility in group 1 was distinctly lower than in group 3 (23.2% vs. 35.7%) and declined in group 1 to 1.8% compared to 20.7% in group 3 after THA. Changes after THA were reported for groups 1 and 2 representing spinopelvic complex key parameter lumbar flexibility (Delta LL), pelvic mobility (Delta SS) and hip motion (Delta PFA), but not for group 3. This is the first study to present age-adjusted normative values for spinopelvic mobility. The subgroups with increased age were identified as risk cohort for altered spinopelvic mechanics and enhanced sagittal spinal imbalance and limited capacity for improvement of mobility after THA. This valuable information serves to focus in the preoperative screening on the THA candidates with the highest risk for abnormal spinopelvic function.
