The Dugdale planning method for high tibial osteotomies underestimates the correction angle compared to the Miniaci method

Purpose The purpose of this study was to compare the planning methods of Dugdale and Miniaci for high tibial osteotomies (HTO) and to assess how their use could influence on the degree of correction and thus the postoperative weight bearing line (WBL). Methods Pre- and postoperative standing hip-knee-ankle (HKA) radiographs were obtained from 70 patients that underwent HTO. The correction angles were determined using Dugdale’s and Miniaci’s methods, and for the latter, both for an opening wedge as well for a closing wedge osteotomy. In a subset of 50 patients, the calculations were performed twice by two observers to calculate inter- and intra-rater reliability. Regression analysis and Bland–Altman plots were used to compare the methods. Whereas the Dugdale method had been used in the planning of the real operations, a regression model was used to predict how the obtained correction would have been if the Miniaci method had been used instead. Results Intra- and inter-rater reliability was excellent for the correction angle for both Dugdale’s (0.992 and 0.991) and Miniaci’s methods (0.988 and 0.987). When planning for an opening wedge osteotomy (OW) and a closing wedge osteotomy (CW), using the Miniaci method and comparing the correction angle with the angle obtained by the Dugdale method, the Miniaci OW and CW angles were larger by a factor of 1.07 (95% CI 1.06–1.08) and 1.10 (95% CI 1.09–1.11). Postoperatively, a mean undercorrection of 2.9° (SD = 2.3) was found. Predicting the correction with use of the calculated Miniaci angles resulted in an undercorrection of 2.5°, indicating that use of the Dugdale method accounted for 14% of the undercorrection. Conclusion It is more likely to underestimate the correction angle when using the Dugdale method compared to the Miniaci method. This could lead to poorer correction accuracy. As the inter-rater reliability is excellent for both methods, choosing to use the Dugdale method on basis of simplicity is not justified. Level of evidence III, Diagnostic study.