Effect of the Osteotomy Length on the Change of the Posterior Tibial Slope With a Simple Distraction of the Posterior Gap in the Uni- and Biplanar Open-Wedge High Tibial Osteotomy.

Purpose To (1) determine the length of the osteotomy at the anterior and posterior cortex, (2) compare between uni- and biplanar osteotomy, and (3) evaluate the relationship between the extent of the osteotomy and change of the posterior tibial slope. Methods A prospective comparative study of 24 uniplanar and 30 biplanar osteotomies was performed. To evaluate the length of osteotomy, osteotomy lines of the anterior and posterior cortex were analyzed in the 3-dimensional surface models. For slope measurement, the intramedullary axis of the proximal tibia (slope P), posterior cortical line of the proximal tibia (slope C), and anterior cortical line of the proximal fibula (slope F) were used. An analysis of the changes in the posterior tibial slope was performed independently using a pre- and postoperative lateral plane radiograph. Results In the uniplanar osteotomy, ratios of the osteotomized length to the total cortical length aligned with the osteotomized plane were larger in the anterior cortex (0.91 in uniplanar v 0.46 in biplanar; P  = 0) and posterior cortex (0.97 in uniplanar v 0.79 ratio in biplanar; P  = 0). Furthermore, the posterior tibial slope was maintained in both groups and the ratios between the anterior and posterior gap in both groups were 0.57 and 0.63, respectively. The maintenance of the slope was not related to any specific variables. Additionally, these phenomena did not differ between those patients who underwent uni- and those who underwent biplanar osteotomy. Conclusions Increase in the posterior tibial slope was prevented with appropriate uni- or biplanar osteotomy with a simple distraction at the most posterior gap. However, in the uniplanar osteotomy, the ratio of the osteotomized length to the total cortical length was larger in both the anterior and posterior cortex. Level of Evidence Level III, case-control study.