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

胫骨小头骨折占老年人骨折总数的10%。由于干骺端骨质丢失，经常发生凹陷性骨折，尤其是胫骨外侧平台，需要手术治疗。塌陷的关节骨折块复位后，仍有干骺端的骨缺损。由于冠骨的脂肪变性，不可能用自体冠骨移植来填充缺损处。取而代之的是使用骨骼替代品。为了在最大负荷下提供足够的稳定性，同时防止继发的复位丢失，需要骨替代和骨接合的组合。磷酸钙骨水泥通常被用作骨替代物，在轴向载荷下提供高稳定性，尽管它们没有可钻探的特性。在磷酸钙和磷酸镁基础上添加或不添加纤维增强的新型双固化矿物水泥是一种有前途的新型骨替代材料。特别是，磷酸镁水泥在凝结时间短后具有很高的稳定性，而且其流变性比磷酸钙水泥更好地控制。这项拨款申请旨在比较这些新型矿物水泥与标准磷酸钙水泥在水泥优化前后的生物力学性能。通过轴向加载和三点弯曲试验，首先对骨替代材料的生物力学性能进行表征。在模拟人工骨中的胫骨头部骨折后，将不同的骨水泥单独和结合螺丝钉接骨术用于填充由此产生的胫骨缺损，然后进行生物力学测试。然后，将通过改变聚乳酸-羟基乙酸(PLGA)纤维、纤维长度和甲基丙烯酸羟乙酯(HEMA)浓度来优化新型矿物水泥的特性。然后，优化的矿物水泥将作为胫骨头部骨折的骨替代品与不同的骨合成物组合进行生物力学测试，并将与标准的磷酸钙骨水泥进行比较。这将包括使用循环加载方案系统地加载标本，以模拟术后部分负重相关的较低负荷和最大加载方案(Zwick Roell Z020，Ulm，德国)。最有希望的骨替代和骨合成组合将在人体骨中进行测试。本研究的主要假设是，与标准磷酸钙骨水泥相比，改性磷酸镁水泥(双固化和纤维增强)与骨合成组合将显示出更好的生物力学性能。

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.