Evaluation of rotational alignment in open wedge distal tibial tuberosity osteotomy using the EOS imaging system: a retrospective cohort study

The present study aimed to evaluate the changes in rotational alignment of the lower extremity under weight-bearing conditions before and after open-wedge distal tibial tuberosity osteotomy (OWDTO) using the EOS imaging system. 63 knees from 63 subjects who underwent OWDTO were included in the present study. Rotational alignment, including femorotibial rotation angle (FTRA) and tibial torsion angle (TTA), and coronal alignment were evaluated by EOS imaging both preoperatively and 6 months postoperatively. Additionally, the correction angle, the tibial osteotomy angle, and the presence of hinge fracture were evaluated by CT scanning 1 week postoperatively. Clinical outcomes were assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS) preoperatively and 6 months postoperatively. The changes in rotational alignment and the association between rotational alignment and other parameters were analyzed. There was no significant difference between preoperative and postoperative FTRA (preoperative: 0.6 ± 4.0°, postoperative: -0.3 ± 3.6°, p = 0.215), but TTA significantly increased (21.1 ± 6.7°, 23.5 ± 6.7°, p < 0.001). The change in TTA was not significantly associated with changes in coronal alignment or other radiological parameters. TTA increased significantly in the group without hinge fractures (ΔTTA: 3.4 ± 3.2°, p < 0.001), whereas no statistically significant change was detected in the group with hinge fractures (ΔTTA: -0.2 ± 2.9°, p = 0.491). Multivariable linear regression analysis demonstrated that hinge fracture remained significantly associated with ΔTTA. No statistically significant associations between ΔTTA and changes in KOOS subscale scores remained after adjustment for multiple comparisons. OWDTO resulted in a significant postoperative increase in TTA, indicating an increase in external tibial torsion, whereas FTRA showed no significant change. A statistically significant increase in TTA was detected only in knees without hinge fractures, and hinge fracture remained significantly associated with ΔTTA in multivariable analysis. These findings suggest that hinge integrity may be associated with postoperative rotational changes after OWDTO, although the clinical significance of this rotational change remains unclear.