Smoking and Unstable Hinge Fractures Cause Delayed Gap Filling Irrespective of Early Weight Bearing After Open Wedge Osteotomy

Purpose: The purpose of this study was to examine the osteotomy gap filling rate with new bone after open wedge high tibial osteotomy (HTO) without bone graft and the effects of smoking, lateral hinge fracture, and early full weight bearing. Methods: A prospective series (N = 70) of open wedge HTOs with the TomoFix plate (DePuy Synthes, Umkirch, Germany) was performed. Radiologic follow-up examinations took place postoperatively, after 6 and 12 weeks, and after 6, 12, and 18 months to measure osteotomy gap filling at each follow-up. Bone healing was compared in smokers versus nonsmokers who underwent open wedge HTOs with intact lateral hinges. Fractured lateral hinges were classified according to the Takeuchi classification and separately analyzed regarding bone healing. Patients were randomly assigned to undergo early (11 days) or standard (6 weeks) full-weight-bearing rehabilitation. Results: A delay in the osteotomy gap filling rate between smokers and nonsmokers could be observed at all follow-up periods, but differences were not significant. A fracture of the lateral hinge was found in 39% of the patients. A type I fracture was observed in 14% of patients, a type II fracture was observed in 13%, and a type III fracture was found in 6%. The highest increase in the osteotomy gap filling rate was observed between 12 weeks and 6 months after surgery in patients with intact lateral hinges. For patients with unstable type II fractures, the highest increase in the gap filling rate was delayed until 6 to 12 months. Early full weight bearing had no effect on the gap filling rate in any of the patient groups evaluated. Conclusions: This study shows that osteotomy gap filling after open wedge HTO is delayed in smokers and in patients in whom opening of the gap resulted in unstable lateral hinge fractures. Early full weight bearing did not have a significant effect on the gap filling rate.