[Computer-assisted kinematic 2D and 3D navigation in medial opening-wedge high-tibial valgus osteotomy]

The aim of the study was to assess the accuracy of axis deformity correction achieved by high-tibial valgus osteotomy either without or with a computer-assisted kinematic navigation system, on the basis of comparing the planned and the achieved frontal axis of the leg. Comparisons of mechanical axis deviation were made using both pre- and post-operative measurements with the planning software and intra-operative measurements with the navigation system before and after osteotomy. In addition, the aim was to test the hypothesis that the use of 3D navigation, as compared with 2D navigation, would help reduce changes in the tibial plateau slope

In the period 2008-2011, high-tibial osteotomy was performed in 68 patients. Twenty-one patients (group 1) underwent osteotomy without the use of navigation and 47 patients (group 2) had osteotomy with a computer-assisted navigation system (32 with 2D navigation and 15 with 3D navigation). Using the planning software, the mechanical leg axis before and after surgery and the anatomical dorsal proximal tibial angle in the sagittal plane were assessed. Medial openingwedge high-tibial valgus osteotomy was carried out in all patients. When using 2D navigation, the mechanical leg axis was measured intra-operatively before osteotomy and then after osteosynthesis which included a simulated axial load of the heel. When using 3D navigation, the procedure was identical and furthermore involved a measurement of the tibial plateau slope obtained with an additional probe in the proximal fragment. The results were characterised using descriptive statistics and their significance was evaluated using the Mann-Whitney U test and Wilcoxon's test, with the level of significance set at p < 0.05.

In group 1, osteotomy resulted in good correction of the mechanical axis in nine patients (43%), inadequate correction in nine (43%) and overcorrection and three (14%) patients. In group 2 with the use of navigation, accurate correction of the mechanical leg axis was achieved in 24 patients (51%), undercorrection was recorded in 21 (45%) and overcorrection in two (4%) patients. The difference in outcomes between the two groups was not statistically significant (p = 0.73). The average correction of the mechanical axis based on comparing measurements on pre- and post-operative radiographs was 9.1 degrees (range, 5-27 degrees); the average correction of the axis visualised intra-operatively was 8.7 degrees (range, 4-27 degrees). The difference was not significant (p = 0.1615) and confirmed our hypothesis that the accuracy of measuring the mechanical axis was not influenced by the method used. The average change in the dorsal slope of the tibial plateau following osteotomy without navigation was 0.9 degrees (range, -8.9 to 9.0 degrees) and that after osteotomy with intra-operative visualisation of the proximal tibial slope was 0.3 degrees (range, -4 to 4 degrees). This difference was not statistically significant (p = 0.813).

A good clinical outcome of high-tibial valgus osteotomy depends on achieving accurate correction of the mechanical leg axis with partial load transfer to the lateral compartment of the knee.

Although the number of cases with good correction was slightly higher in the patients undergoing osteotomy with navigation, the difference was not significant. Intra-operative visualisation of the mechanical axis proved sufficiently accurate on comparison with the pre-operative planning based on weight-bearing radiography of the leg. A simulated axial load of the heel included in the kinematic navigation system does not sufficiently correspond to normal weight-bearing and therefore an undercorrection of the deformity might occur. Using 3D navigation had no marked effect on a change in the slope of the tibial plateau.