Effect of posteriorly inclined sagittal osteotomy on posterior tibial slope in biplanar medial opening wedge high tibial osteotomy: a case series study

Background Medial opening wedge high tibial osteotomy aims to correct coronal plane deformities and redistribute the load in varus-aligned knees. However, changes in the sagittal plane during medial opening wedge high tibial osteotomy can influence the posterior tibial slope, potentially affecting knee biomechanics. The sagittal inclination angle of the osteotomy, which is the angle between the medial joint line and the osteotomy line on lateral view, is a relatively new parameter that has been discussed in the literature, as a factor influencing the posterior tibial slope. The aim of this study is to investigate success rates in achieving the targeted postoperative slope, which is to avoid increasing the slope, with posteriorly inclined sagittal osteotomy. Methods This research was designed as a retrospective single-center case-series study. In order to avoid increasing the posterior tibial slope, our modified surgical technique involves adjusting the sagittal inclination angle to be 10o posteriorly inclined. This angle was considered to be posteriorly inclined if the anterior portion of the osteotomy was inclined proximally. Pre- and postoperative posterior tibial slope measurements were recorded. Changes in postoperative tibial slope compared to preoperative tibial slope were statistically evaluated using the paired t-test. Changes were categorized as decreases, no change, or increases, and these three groups were compared using the one-sample binomial test. Results Ninety-five patients (77 women and 18 men) with a mean age of 52.8 +/- 7.0 were included in this study. The preoperative mean posterior tibial slope was measured as 12.5 +/- 3.9 degrees and the postoperative mean PTS was 10.6 +/- 4.3 degrees. A paired t-test revealed a statistically significant difference of 1.9 +/- 3.8 degrees (95% confidence interval: 1.13-2.71; p < .01). In four cases (4.2%), the PTS remained the same, while for 67 patients (70.5%) the PTS decreased and for 24 patients (25.3%) the posterior tibial slope increased. Therefore, a decrease or no change in the posterior tibial slope was achieved in 74.7% of all cases (p < .01). Conclusions Modifying the sagittal inclination angle to achieve a posteriorly inclined osteotomy during medial opening wedge high tibial osteotomy may prevent increasing the posterior tibial slope in the majority of cases.