What is the relationship between the "Fujisawa point" and postoperative knee valgus angle? A theoretical, computer-based study

Background: The purpose of this study was to determine the relationship between the Fujisawa point and postoperative knee valgus angle and the anatomical factors influencing this relationship. Methods: An experimental study was conducted including 116 patients with medial compartment knee osteoarthritis undergoing treatment with open-wedge high tibial osteotomy (OWHTO). Each patient received simulated HTO through the Fujisawa point in the picture archiving and communication system (PACS). The preoperative hip-knee-ankle (HKA) angle and lower extremity anatomical parameters were recorded before the computerized HTO simulation. The postoperative knee valgus angle was measured after this procedure. A second simulation HTO was performed to adjust the mechanical axis to the optimal valgus angle (4.5) and calculate the percentage of the tibial plateau width where the Mikulicz line crossed the knee. The Spearman correlation test and multivariate regression were used for analysis. Results: The median preoperative MA varus angle of this study cohort was 174.1 degrees (170.8, 176.2 degrees). The median knee valgus angle after simulated osteotomy through the Fujisawa point was 2.4 degrees (2.1, 2.7 degrees). The valgus angle was positively correlated with the tibial plateau width (r = 0.23, p = .013) and preoperative HKA angle (r = 0.32, p < .001). Multivariate regression analysis showed that the preoperative HKA angle was a significant contributor to the postoperative valgus angle. When conducting the osteotomy with the optimal valgus angle (4.5 degrees), the percentage of the Mikulicz line passing through the tibial plateau was 71.93% (67-78%). Conclusions: The preoperative HKA angle affects the postoperative valgus angle after HTO. If the optimal valgus angle of 4.5 degrees is desired, a more lateral position of the Fujisawa point should be targeted during OWHTO, which accounts for approximately 71.9% of the tibial plateau. (C) 2019 Elsevier B.V. All rights reserved.