Comparison of Anatomical Conformity between TomoFix Anatomical Plate and TomoFix Conventional Plate in Open-Wedge High Tibial Osteotomy

Abstract

Background and Objectives: The TomoFix anatomical plate was developed to improve plate position, proximal screw direction, and post-correction tibial contouring. The purpose of this study was to compare postoperative configurations between the TomoFix anatomical plate and the TomoFix conventional plate. It was hypothesized that the new modified plate provides a better fixative coaptation than the conventional plate. Materials and Methods: A total of 116 cases (112 patients) were enrolled in this study from March 2015 to February 2021. Among them, 63 patients underwent surgery using the TomoFix conventional plate, and 53 underwent surgery using the TomoFix anatomical plate. The radiographic outcomes, including the hip−knee−ankle (HKA) angle, medial proximal tibial angle (MPTA), tibial slope, plate angle, proximal screw angles, and plate-to-cortex distance at #1 hole (just below the osteotomy site) were compared between the two groups. Results: Patients with the TomoFix anatomical plate showed similar results in terms of the pre- and postoperative HKA angle, MPTA, and tibial slope. The TomoFix anatomical group showed a significantly greater plate angle (39.2° ± 8.1° vs. 31.7° ± 7.0°, p < 0.001) and less screw angles, indicating that the TomoFix anatomical plates allowed a more posterior plate position than the conventional plate. The plate-to-cortex distance was significantly less in the TomoFix anatomical group than in the TomoFix conventional group (p < 0.001). Conclusion: The TomoFix anatomical plate showed a more posteromedial plating position, better proximal screw direction to the lateral hinge, and improved post-correction tibial contour compared to the TomoFix conventional plate.

Keywords: TomoFix; anatomical conformity; high tibial osteotomy; plate position.

Figure 1

(A) Schematic diagram of the new plate lateral view. While the previous plate was a 90° T-shaped plate with no left and right distinction, the TomoFix anatomical plate has a 5° posterior slope, allowing the plate to be positioned relatively backward. As a result, the new plate system (B) enables parallel screw fixation than the previous plate (C).

Figure 2

Measurement of the plate angle and screw angles on the CT axial scan. (A) The plate angle was defined as the angle between the anteroposterior line connecting the proximal part of the plate and the posterior tibial condylar line. (B) The A, B, and C screw angle was defined as the angle between the line drawn along the screw and the posterior tibial condylar line. (A, B, and C screws from anterior to posterior, respectively).

Figure 3

Measurement of the plate-to-cortex distance at #1 hole. It was defined as the distance between the inner surface of the plate and the outer surface of the tibial cortex at #1 hole.