Biomechanical investigation of different internal fixations in medial opening-wedge high tibial osteotomy

Background. The medial opening-wedge osteotomy for treatment of varus gonarthritis has become very popular in recent years. Different implants for internal fixation after the osteotomy have been created. It is still unclear, which principle of internal fixation (angle stable or non-angle-stable plate with or without spacer) has the best biomechanical properties. The aim of this study was to determine the biomechanical properties of different fixation techniques in medial opening-wedge high tibial osteotomy in a porcine bone model. Methods. A 10-mm high tibial opening-wedge osteotomy was performed and stabilized with plates of similar dimensions but different functional principle (conventional plate, angle stable plate with or without spacer). Biomechanical properties (stiffness, displacement within the osteotomy space and load at failure) were evaluated under axial load. Results. Plates which contain a spacer had a significantly higher stiffness at a load at 1000 N (p < 0.05). This correlates with a significantly reduced deformation within the osteotomy space. The strength at failure was not different between the groups. The use of a spacer in a conventional plate produces fractures of the lateral tibial cortex. In angle stable plates and plates containing spacers, the failure was caused by fractures of the lateral tibia surface, the fibula or by displacement within the tibio-fibular joint. The failure was caused primarily by implant insufficiency in plates without spacers. Conclusions. In a model with comparable conditions, implants which contain a spacer have superior biomechanical properties. Angle stable plates may prevent fractures of the lateral cortex after opening-wedge osteotomy.