Static and Dynamic Differences in Fixation Stability between a Spacer Plate and a Small Stature Plate Fixator Used for High Tibial Osteotomies: A Biomechanical Bone Composite Study

Background. The objective of the present study was to compare mechanical strength and stability of the newly designed spacer plate with the gold standard plate for the treatment of medial knee joint osteoarthritis. Materials and Methods. Ten fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomy (HTO) according to standard techniques, using five TomoFix plates and five Contour Lock plates. Static compression load to failure and load-controlled cyclical fatigue failure tests were performed. Forces and horizontal displacements were measured; plastic deformations and dynamic stiffness were determined. Results and Discussion. In all samples, rotation of the tibial head and fracture of the opposite cortex were observed. Behaviors of the specimens under static loading were comparable between groups. Cyclic testing revealed lateral significant higher stiffness until failure for the Contour Lock compared to the TomoFix plate. No visible implant failure was observed in any group. Conclusion. Considering the static analysis, both plates offered sufficient stability under physiologic loads of up to 3000？N. The Contour Lock plate-fixated specimens showed a higher stability during the cyclic testing, supposedly due to the wider distance between the fixation screws. 1. Introduction High tibial closing wedge osteotomy is a well-established treatment for medial femorotibial osteoarthritis in the varus knee. The goal of osteotomy is a slight valgus overcorrection to shift the load to the intact lateral compartment of the femorotibial joint. Although clinical results after high tibial osteotomy often are encouraging, some factors are associated with a poor long-term outcome such as imprecise osteotomy or loss of the primary correction angle. A fractured lateral cortex of the proximal tibia may lead to loss of valgus correction before bony fusion is achieved and may even necessitate reoperation. In larger correction (<8°), an opposite cortex fracture is frequent and inevitable. In these cases, maintenance of correction depends solely on the primary implant stability prior to complete healing. For the time being, the long and rigid T-shaped internal fixator (TomoFix, Synthes Gmbh, Oberdorf, Switzerland) seems to be the gold standard since it provides sufficient primary stability until solid bone healing is achieved. In addition, the TomoFix has a narrow proximal design which allows for a biplanar osteotomy, thus enlarging the surface for rapid contact healing [1, 2]. However, newly designed angle-stable implants (Contour Lock HTO,