Faster Early Union but No Long-Term Functional Advantage: Orthotopic Bone Flap Transplantation versus Allograft Bone Grafting in Medial Open-Wedge High Tibial Osteotomy

<title>Abstract</title> <p>Background Delayed union of the osteotomy gap remains a common concern after medial open-wedge high tibial osteotomy (OW-HTO), particularly in patients with large correction gaps. Orthotopic bone flap transplantation has recently been introduced as a novel autologous grafting technique to enhance gap healing. This study aimed to compare radiographic and clinical outcomes between orthotopic bone flap transplantation and allograft bone grafting in OW-HTO. Methods This retrospective cohort study included 70 patients who underwent OW-HTO between December 2023 and June 2024. Patients were assigned to either the orthotopic bone flap group (n = 40) or the allograft group (n = 30). The primary outcome was osteotomy gap union rate at 3, 6, 12, and 18 months postoperatively, assessed using serial radiographs. Secondary outcomes included lower-limb alignment parameters (hip-knee-ankle angle, femorotibial angle, and medial proximal tibial angle), perioperative blood loss, and clinical outcomes assessed by WOMAC, Lysholm, and KOOS scores. Multivariable linear regression was performed to identify factors associated with delayed union. Results The orthotopic bone flap group demonstrated significantly higher osteotomy union rates at 3 months (38.07 ± 2.65% vs 35.92 ± 2.53%, p = 0.001) and 6 months (59.25 ± 3.59% vs 55.25 ± 4.02%, p &lt; 0.001) compared with the allograft group. No significant between-group differences were observed at 12 months or final follow-up (p &gt; 0.05). Patients receiving orthotopic bone flap transplantation experienced greater overt and hidden blood loss (both p &lt; 0.01). No significant differences were found in postoperative alignment correction or functional outcomes between groups at 6 months or final follow-up. Multivariable analysis identified advanced age, higher body mass index, and diabetes mellitus as independent risk factors for delayed osteotomy healing, whereas orthotopic bone flap transplantation was associated with faster early union. Conclusion In patients undergoing OW-HTO, orthotopic bone flap transplantation was associated with faster early radiographic healing of the osteotomy gap compared with allograft bone grafting. However, this advantage did not translate into superior functional outcomes or long-term healing and was accompanied by increased perioperative blood loss.</p>