Study of stress distribution under the influence of bending load in models of different options for osteosynthesis of tibia bones with fractures in the middle third of their congenital pseudarthrosis in children with incomplete growth

Abstract

Congenital pseudoarthrosis of the bones of the lower leg is a rare disease characterized by the presence of non-union (pseudoarthrosis) of the bones of the lower leg, which does not grow independently. The majority of surgical techniques involve the removal of pathological soft tissues in the zone of pseudarthrosis followed by bone autoplasty and fixation of tibial bone fragments in external fixation devices or with the help of intramedullary fixators. Purpose - to investigate the stress-deformed state of models of the leg in the presence of pseudarthrosis in the middle third under the influence of bending load and their osteosynthesis using intramedullary rods of various designs in children with incomplete growth. Materials and methods. Mathematical modeling of 3 variants of osteosynthesis of lower leg bones with congenital pseudarthrosis in the middle third was performed: 1 - rod without rotational stability; 2 - rod with rotational stability; 3 - rod with rotational stability and blocked movement during compression. The stress-strain state of the models under the influence of a bending load of 300 N was studied. Results. When using a rotationally unstable «growing» rod, maximum stress levels of 18.5 MPa and 23.1 MPa are determined at the proximal and distal ends of the tibia, respectively. In the fracture zone, the stress level is minimal and does not exceed 0.2 MPa. In the diaphyseal part, stresses are determined at the level of 0.3 MPa and 0.4 MPa above and below the fracture zone, respectively. In the zone of the fracture of the fibula, the stress level is also not significant - 0.7 MPa and 0.8 MPa in the proximal and distal fragments. The use of a rod with rotational stability does not lead to any significant changes in the stress-strain state of the model compared to tibial osteosynthesis with a rotationally unstable rod. The use of an intramedullary rod with blocked movement during compression allows to reduce the values of stresses at the proximal and distal ends of the tibia - up to 16.9 MPa and 21.2 MPa, respectively. In all control points of the diaphyseal part of the tibia, the stresses are minimal and equal to 0.2 MPa. It should be noted that in this case the stresses in the area of the fracture of the fibula, where they do not exceed the mark of 0.1 MPa, are almost negligible. Conclusions. Under bending loads, all types of intramedullary rods provide a minimum level of stress in the tibial fracture zone. Additional rotational and longitudinal stability of the rods allow to slightly reduce the level of stress in the proximal and distal ends of the tibia. The research was carried out in accordance with the principles of the Helsinki Declaration. The study protocol was approved by the Local Ethics Committee of the participating institution. The informed consent of the patient was obtained for conducting the studies. No conflict of interests was declared by the authors.