Recently, the medial opening wedge high tibial osteotomy (OWHTO) with a locking plate has attracted a great deal of attention. However, previous studies reported complications after OWHTO with a TomoFix plate, such as skin irritation, lateral hinge fracture, implant failure and so on. Therefore, we have developed a novel fixation system (TriS Plate, Olympus Terumo Biomaterials). 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 and allow subcutaneous, minimally invasive application and fixation, without an adjustment of the plate. The purpose of this study was to compare clinical results of TriS and TomoFix plates in OWHTO.
Consecutive 205 patients (209 knees) who underwent OWHTO were enrolled in this study between 2011 and 2018. In the first 133 knees, the TomoFix plate was fixed to the tibia between 2011 and 2014 (Group F). In the remaining 76 knees, the TriS plate was fixed between 2015 and 2018 (Group S). All patients underwent clinical, radiological, and CT evaluations before surgery and at 3 years after surgery. Statistical analyses were made using the Mann-Whitney U test and Student t test. Significant level was set at p = 0.05.
There was no significant difference in the background factors between the 2 groups. Postoperatively, the mean functional knee score (Japan Orthopaedic Association score) significantly improved from 66 to 91 points (p<0.0001). At the final examination, the lateral femorotibial angle changed significantly from 180° to 169°. The mechanical axis percentage shifted to a point 68% lateral from the medial edge of tibial plateau. Concerning the postoperative knee alignment and clinical outcome, there was no statistical difference in each parameter between the 2 groups. Regarding postoperative irritation of the subcutaneous tissue around the plate, the visual analog scale pain scores was significantly greater (p<0.0001) in Group F than in Group S. CT examination showed that there was a significant difference (p<0.0001) in the plate position between Groups S and F. The screw angle was significantly lower (p<0.0001) in Group S than in Group F. The distance from the screw to the popliteal artery was significantly shorter (p<0.0001) in Group F than in Group S. During plate removal, in Group F, 14 locking screws were found to be broken in 9 knees (7%). In Group S, we confirmed no implant failure.
The medial knee pain had resolved in all cases. In the plate positon, the TriS plate was fixed posteriorly at the proximal tibia. The TriS screw was also inserted more parallel to posterior cortex of the tibia. The mechanical axis usually passes through the posterior aspect of the proximal tibia. Therefore, previous studies reported that an application of the plate in a more posterior position provides greater stability. The position of the proximal screw affects not only the stability of the osteotomy site but also the safety during surgery. The use of TriS plate system is thus likely to improve the initial axial and possibly rotational stability at the osteotomy site.