The Impact of Opening Wedge High Tibial Osteotomy on Spinal Alignment.

Introduction Flexion contracture of the knee has been reported to induce forward trunk inclination and pelvic retroversion, whereas the progression of pelvic retroversion may further exacerbate knee joint symptoms, suggesting a close relationship between the knee and spinal alignment. The purpose of this study was to investigate the effects of lower limb alignment changes after opening wedge high tibial osteotomy (OWHTO) on spinopelvic sagittal alignment. Methods We retrospectively analyzed 34 knees that underwent OWHTO for medial compartment knee osteoarthritis between 2023 and 2025. Standing full-length lower limb and whole-spine radiographs were obtained preoperatively and at one year postoperatively. Lower limb alignment parameters, i.e., the percentage of mechanical axis (MA), mechanical medial proximal tibial angle (mMPTA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), and posterior tibial slope (PTS), were evaluated. Spinopelvic parameters included pelvic tilt (PT), sacral slope (SS), pelvic incidence (PI), thoracic kyphosis (TK), lumbar lordosis (LL), and the mismatch between PI and LL (PI-LL) Clinical outcomes were assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS) before surgery and at one year postoperatively. Correlations between postoperative spinopelvic parameters and clinical outcomes were also examined. Results Pelvic tilt and the mismatch between PI and LL significantly decreased following OWHTO (p = 0.003 and p = 0.044, respectively), indicating improvement in spinopelvic sagittal alignment. However, no significant correlations were found between changes in spinal alignment and postoperative scores on the KOOS. Conclusion Both pelvic tilt and the mismatch between PI and LL, which reflect lumbopelvic alignment, were significantly decreased after OWHTO. This may have arisen because the correction of knee alignment improved the load distribution in the lower limbs, which in turn contributed to the improvement of lumbopelvic alignment. Our findings suggest that OWHTO not only corrects lower limb alignment but may also have a positive effect on lumbopelvic alignment.