Summary

The use of the TriS plate system provides better stability with its optimal placement and rigid fixation without the residual pain around the plate and implant failure.

Abstract

Introduction

Recently, the medial open-wedge (OW) high tibial osteotomy (HTO) with a locking plate has attracted a great deal of attention. However, previous studies reported complications after OWHTO with a conventional locking plate (TomoFix, DePuy Synthes), such as pseudoarthrosis, lateral hinge fracture, and implant failure (KSSTA 2014). Therefore, recently, we have developed a newly fixation system (TriS Medial HTO Plate System; Olympus Terumo Biomaterials) for OWHTO. First, the TriS plate consists of an anatomically shaped titanium alloy plate and cannulated locking screws. Secondly, this plate can be located just medial side of the proximal tibia. Thirdly, the shape of the plate is adapted to the corrected medial cortex of the proximal tibia. Recently, new TomoFix anatomical (DePuy Synthes) has been introduced. The purpose of this study was to compare clinical outcomes and plate positions of 2 systems in OWHTO.

Methods

A prospective comparative cohort study was conducted with eighteen consecutive patients (20 knees) who underwent OWHTO with a locking plate between March 2017 and October 2017. There were 13 women and 5 men with a mean age of 67 (44-80) years. All patients were randomly divided into the two groups in 10 knees each; Group S (TriS plate) and Group F (TomoFix anatomical). In surgical procedure, we performed a biplanar osteotomy of the tibia. Beta-TCP spacer was implanted into the opening space. Then, a locking plate was implanted onto the tibia. All patients underwent clinical, radiological, and CT evaluations before surgery and at 12 months after surgery. The study design had been accepted by the institutional review board clearance in our hospital. Concerning CT evaluation, a posterior reference line (PL) was drawn tangent to the posterior contour of the medial and lateral cortex on the axial view of the proximal tibia. The anteroposterior length of the proximal tibia (AP1) and the distance between the anterior edge of the tibia to the center of the proximal plate (AP2) were measured perpendicular to the PL. The plate position was defined with the %AP2/AP1. For each proximal-posterior screw, the screw angle was defined as the angle between the screw axis and the PL on the axial view of the tibia. The distance from the proximal-posterior screw axis to the center of the popliteal artery was measured perpendicular to the proximal-posterior screw axis. Statistical comparison was made with Mann-Whitney U test. Significant level was set at p = 0.05

Results

1) There was no significant difference in the background factors between the 2 groups. 2) Radiological evaluation: the lateral femorotibial angle changed to 170° in each group. The weight-bearing line (WBL) percentage shifted to pass through a point 65% lateral from the medial edge of tibial plateau. Concerning the post-operative knee alignment, there was no statistical difference in each parameter between the 2 groups. 3) CT evaluation: There was a significant difference (p=0.035) in the plate position between Groups S (30.4+/-12.2%) and F (17.4+/-13.2%). There were no significant differences in the screw angle and the distance to the popliteal artery between the 2 groups. 4) Clinical evaluations: Postoperatively, the functional knee score (Japanese Orthopaedic Association scrore) significantly improved in each group. Proximal locking screw breakage was observed in 10% of the cases in Group F. We also evaluated the residual pain around the plate using visual analog scale (VAS). Regarding the VAS score, Group S was significantly (p=0.034) lower than Group F. There was a significant correlation (p<0.001) between the plate position and the residual pain around the plate.

Discussion

The TriS plate was posteriorly fixed onto the proximal tibia. Previous studies reported that application of the plate in a more posterior position provides greater stability. The use of the TriS plate system provides better stability with its optimal placement and rigid fixation without implant failure.

Conclusion

The clinical scores significantly improved in all cases after OWHTO with a TriS plate. This plate system produces superior stability and safety for bony fixation in OWHTO.