Influence of the angle of inclination of the load vector on the strength of the biodegradable screw for blocking intramedullary osteosynthesis

Abstract

Problem statement . Diaphyseal fractures of the tibia occupy a leading place among the fractures of the long tubular bones. Today, doctors prefer minimally invasive osteosynthesis methods that are not related to the application of additional injury to the soft tissues in the area of the fracture. The most effective method of osteosynthesis, with diaphyseal fractures of the tibia, is a closed blocking intramedullary osteosynthesis (BIOS). The advantages of a closed BIOS are its minimal invasiveness, as well as the possibility of an early load on a broken limb. Since it is very important for the consolidation of a fracture that the bone implant system be in constant dynamic stress, it sometimes becomes necessary to perform a fracture dynamization operation, which consists in removing the locking screw. It is possible to improve the results of treatment of patients with extra-articular tibial fractures by using screws made of biodegradable materials. The essence of these materials is that they can dissolve over time. This reduces their strength characteristics. Thus, after a certain time the biodegradable screws can be broken when loaded, i.e. will enable the implementation of a staged dynamization of a fracture at a given time. Purpose. Assessment of the influence of the value of the angle of inclination of the vector of the load on the strength of a screw made of a biodegradable alloy, which is used in BIOS. Conclusion. As a result of the study, a function of normal stresses arising in a dangerous section of the screw, depending on the magnitude of the slope of the load vector, was obtained. Analysis of this function showed that normal stresses reach extreme values when the angle values are close to 90°. The results indicate that as a design scheme, you can use a model in which the load is perpendicular to the axis of the screw.