Bridging the Gap. Is Augmentation Necessary During Opening-Wedge High Tibial Osteotomy?: Commentary on an article by Seong Chan Kim, MD, et al.: "Comparative Analysis of Serial Union Patterns After Opening-Wedge High Tibial Osteotomy with and without Bone-Void Fillers".

Commentary High tibial osteotomy of the knee is used to treat varus malalignment associated with unicompartmental osteoarthritis as well as instability and also can be combined with medial compartment cartilage-repair procedures. Various techniques exist; the lateral closing-wedge osteotomy is considered the traditional approach but is technically demanding and has been associated with major complications1. To minimize this complication profile and to improve on the technical challenges, the opening-wedge high tibial osteotomy was developed. However, that procedure presents different challenges specifically related to bone union of the opening wedge and stabilization of the gap during healing. In a study by Martin et al.1, 323 consecutive opening-wedge high tibial osteotomies were evaluated to provide a comprehensive description of adverse event rates, categorized by severity, and their effect on patient-reported outcomes. Overall, the authors noted that the rate of severe adverse events was 7%, with the most common being nonunion (3.2%). Furthermore, the most common event requiring nonoperative treatment was delayed union (12%). With this issue of nonunion and delayed union in mind, Kim et al. sought to determine if bone-void fillers were necessary to achieve bone union of the opening gap following opening-wedge high tibial osteotomy. The authors retrospectively evaluated 97 patients who had undergone primary opening-wedge high tibial osteotomy with an opening gap between 8 and 15 mm. The cases were divided into 3 groups, with either hydroxyapatite chip bone graft, allogeneic chip bone graft, or no bone graft being utilized at the gap site. Based on the radiographic evaluations performed, it was noted that the group that had received no bone graft had slow bone union progression up to 6 weeks but demonstrated more prominent progression of gap filling compared with the other groups at 6 months postoperatively. At the 1-year postoperative time point, a similar degree of union was observed among all groups. Furthermore, the bone union pattern did not correlate with the degree of correction after the 3-month postoperative time point in all groups. The findings of this study call into question the need for a bone-void filler when performing an opening-wedge high tibial osteotomy. As the authors note, their findings confirm the results of a systematic review by Slevin et al.2 that evaluated the outcomes and complications after opening-wedge high tibial osteotomy. In that review of 22 articles reporting the results of 1,421 opening-wedge high tibial osteotomies, the use of synthetic bone substitutes could not be recommended as there were no definitive advantages with any bone-void filler in terms of union rates and loss of correction. While synthetic bone substitutes may not improve union rates after opening-wedge high tibial osteotomy, autograft bone-filled osteotomies might be considered a superior alternative. Lash and colleagues3, in a systematic review, noted the lowest rates of delayed union/nonunion following opening-wedge osteotomies around the knee filled with autograft bone. However, 2 more recent studies have questioned the superiority of autograft augmentation during opening-wedge high tibial osteotomy4,5. In a systematic review and meta-analysis evaluating whether bone-grafting is necessary for opening-wedge high tibial osteotomy, Ren et al.4 reported that the overall estimate demonstrated no significant difference in the loss of correction or complications between the groups treated with either autograft, allograft, or no fill. Interestingly, the no-fill group had statistically better Knee Society scores. Those findings were confirmed in the study by Fucentese et al.5, who evaluated 15 patients undergoing opening-wedge high tibial osteotomy with iliac crest autograft augmentation and 25 patients undergoing opening-wedge high tibial osteotomy without bone-void filler. While the iliac crest augmentation significantly increased healing of the osteotomy gap, no functional advantage was found in comparison with the group without a bone-void filler at 3 or 12 months postoperatively. Based on their findings, the authors could not recommend the routine use of iliac crest autograft during opening-wedge high tibial osteotomy. The findings of the study by Kim et al. support and confirm the current literature that bone union-related issues and clinical outcomes after opening-wedge high tibial osteotomy may not be impacted by the material utilized to fill the wedge. Instead, the problems involving delayed union and nonunion are more likely to be related to a combination of multiple factors, including wedge size, plate type, fracture of the lateral hinge, smoking, body mass index, and the postoperative weight-bearing protocol1. Future research will need to control for these multiple factors and their complex interplay in order to identify the underlying issues of concern.