Essential Safety Considerations for Total Hip Arthroplasty: Pelvic and Spine Alignment Across Age Groups in Women at an Osteoporosis Outpatient Clinic—A Retrospective Observational Study

<b>Background/Objectives</b>: Pelvic incidence (PI) is deeply related to spinal sagittal alignment. Previous reports have demonstrated a deep association between PI and anatomical sacral slope (a-SS), underscoring the utility of a-SS in estimating PI. The investigation of temporal changes in pelvic and spinal alignment in healthy individuals is crucial for conducting surgical interventions such as total hip arthroplasty; however, these changes remain undocumented. There have been a few Japanese reports on this topic. This study explores the relationship between aging-related changes and pelvic and spinal sagittal alignment. <b>Methods</b>: By employing the methodology from a study by Imai et al., we analyzed the anterior pelvic plane (APPA), PI, pelvic tilt (PT), sacral slope (SS), a-SS, anatomical pelvic tilt (a-PT), thoracic kyphosis angle (TK), and lumbar kyphosis angle (LL), to determine the degree of kyphosis in healthy individuals. <b>Results</b>: APPA decreased over time, SS altered gradually, and PT underwent more pronounced variations with age; however, PI did not change significantly. a-SS changed early and was lower in the younger group than in the older group. Moreover, a-PT decreased with age. Spinal sagittal alignment was similar between the younger and older groups, changing gradually in LL and earlier in TK than in LL. <b>Conclusions</b>: Pelvic changes are compensated for by the pelvis, and TK changes, i.e., spinal alignment changes, are compensated for by the LL. The posterior pelvic tilt progresses with age, moving from compensation at the sacroiliac joint to compensation at the sacrum.