Biomechanical analysis of different mineral bone substitutes for application in tibial head bone defects

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Tibial head fractures account for 10% of all fractures in the elderly. Due to metaphyseal bone loss, depression fractures, especially of the lateral tibial plateau, frequently occur and need to be treated operatively. After reduction of the depressed articular fracture fragment, a metaphyseal bone defect remains. Filling the defect with an autologous crest bone graft is not possible because of fatty degeneration of the crest bone. Instead, bone substitutes are used. To provide enough stability under maximal loading while preventing a secondary loss of reduction, a combination of bone substitute and osteosynthesis is needed. Calcium phosphate cements are usually used as bone substitutes, providing high stability under axial loading, although they have no drillable characteristics. New dual-setting mineral cements with or without fibre-reinforcement on a calcium phosphate and magnesium phosphate base are promising new bone substitute developments. Magnesium phosphate cements, in particular, provide high stability after a short setting time and are better to control in their rheological qualities than calcium phosphate cements. This grant application aims to compare the biomechanical properties of these new mineral cements relative to standard calcium phosphate cements, before and after the cements have been optimized. Using axial loading and 3-point-bending tests, the biomechanical properties of the bone substitutes will firstly be characterized. After simulating tibial head fractures in synthetic bones, the different cements will be used to fill the resulting tibial bone defects, in isolation and in combination with a screw osteosynthesis, and then biomechanically tested. Characteristics of the new mineral cements will then be optimized by modifying the polylactic-co-glycolic acid (PLGA) fibres, the length of the fibres and the 2-hydroxyethylmethacrylate (HEMA) concentration. The optimized mineral cements will then be biomechanically tested as bone substitutes for tibial head fractures in combination with different osteosyntheses and will be compared to a standard calcium phosphate cement. This will involve the specimens being systematically loaded using a cyclic loading protocol to simulate the lower loads associated with postoperative partial weight bearing and in a maximal loading protocol (Zwick Roell Z020, Ulm, Germany). The most promising bone substitute and osteosynthesis combinations will then be tested in human bones.The main hypothesis of this research is that the modified magnesium phosphate cements (dual-setting and fibre reinforced) in combination with osteosyntheses will display superior biomechanical properties compared to standard calcium phosphate cements.