Spinopelvic alignment changes after unilateral total knee arthroplasty associated with functional recovery

Abstract Background The biomechanical interaction between knee pathology and spine–pelvis alignment in advanced knee osteoarthritis (KOA) has received increasing attention. This study evaluated short-term changes in spinopelvic alignment after unilateral total knee arthroplasty (TKA) and examined their associations with functional outcomes. Methods This observational cohort study included 100 patients who underwent unilateral TKA between November 2022 and November 2023. Standing whole-spine radiographs were obtained preoperatively and 6 months postoperatively. Sagittal parameters included spinal tilt (ST), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), sagittal vertical axis (SVA), and PI–LL mismatch. Coronal parameters included Cobb angle, C7 plumb line–central sacral vertical line distance (C7PL–CSVL), and iliac obliquity (IO). Functional outcomes were assessed using the Knee Society Score (KSS) and instrumented timed up and go (iTUG) test. Results At 6 months after TKA, ST, LL, and SS increased significantly, whereas PT, SVA, and PI–LL mismatch decreased significantly; PI remained stable. Cobb angle, C7PL–CSVL, and IO also decreased significantly. KSS increased and iTUG time decreased. Multivariable analyses showed that selected preoperative sagittal and coronal parameters, as well as their postoperative changes, were associated with postoperative functional outcomes. These findings describe concurrent short-term radiographic and functional changes and do not establish a causal effect of TKA on spinopelvic alignment. Conclusions Unilateral TKA was followed by short-term changes in standing sagittal and coronal spinopelvic parameters at 6 months. These radiographic changes were associated with functional outcomes, but should be interpreted as early flexible postural readaptation rather than structural remodeling of the spine–pelvis complex. Further studies with longer follow-ups are needed to determine whether these changes persist.