Fatigue analysis model for applying bioglass–hydroxyapatite biocomposite LCP bone fixation plates to fix humeral shaft fractures

Abstract

Generally, there are several methods to treat patients who suffer from humerus fractures caused by accidents, such as internal fixation, external fixation, and a nail system. Bone fixation with locking compression plates (LCPs), one of the most famous internal fixation methods, is used to treat humerus shaft fractures. However, cracks and fractures can occur on the plate before the humerus fracture is completely rejoined, in which case the patient needs another surgery. There were two main purposes for this research: one was to find suitable forming conditions of LCPs synthesized from biomaterials, and the second was to obtain a suitable fixation method using LCPs. For the former, hydroxyapatite powder from bovine bone was synthesized, and bioactive glass powder from mollusk shell was prepared with chemical reactions. The materials were blended and ground with a high-speed ball milling machine to reduce and thoroughly mix them before forming the proposed materials. A hydraulic pressing machine was then used to compress the formed composites. The Taguchi experimental design was used to evaluate essential factors of forming conditions, such as sintering temperature, compacting pressure, mixing ratio, and holding time for pressing. The results demonstrate that a ratio of bioactive glass to hydroxyapatite of 30:70 wt%, 30 MPa compacting pressure, and 5000 °C sintering temperature provided the highest compressive and bending strength of 249.46 MPa and 29.16 MPa, respectively. The bulk density of the specimen was 3.16 g/cm3, and the biomaterials, tested by lactate dehydrogenase (LDH) analysis, can be used on the human body since it they are biodegradable in 3980 days, which is long enough for bone healing. For the second purpose, the S-N curve of the specimen was obtained via experiment and then used to create a finite element model of bone fixation using LCPs. Important factors of fracture gap, number of screws on the plate, and axial compression force were considered in finding suitable bone fixation conditions in the finite element model. Based on the response surface method (RSM), the results of statistically significant factors showed that the axial compression force was 182 N by using six screws, resulting in the greatest fatigue life. The results of this paper could assist orthopedic surgeons in understanding the biomechanical efficiency of bone fixation using LCPs. In addition, surgeons can select a fixation technique based on the patient’s condition using the numerical results from this study.