MATHEMATICAL MODELING OF OSTEOSYNTHESIS OF THE LOWER LEG BONES DURING THEIR CONGENITAL PSEUDARTHROSIS IN THE MIDDLE THIRD

Abstract

Congenital pseudarthrosis of the tibia remains a serious problem in pediatric orthopedics through a high percentage of poor results due to the inability to achieve fusion of the tibia. Purpose. To study the stress-strain state of the models of the lower leg with pseudoarthrosis of its bones with various variants of their osteosynthesis. Object and methods. A model of the distal end of the lower extremity was built, which contained the tibia and fibula, foot bone. The non-fusion zone of the lower leg bones was modeled in their middle third and 3 variants of osteosynthesis: intramedullary shaft and knitting needles; a core, knitting needles and a block of bone grafts on the tibia; block on both lower leg bones. Osteosynthesis of the tibia was modeled by intramedullary rods with longitudinal mobility: with and without rotational stability. Models were loaded by compression and torsion. Results. Osteosynthesis of the tibia with a rotationally unstable shaft reduces the level of stress in its metaphysical zones to 1.0 MPa. Maximum stresses were observed around the fracture of the fibula – 7.8 MPa. The use of a rotationally stable rod does not lead to significant changes. A block of bone grafts reduces stress to 1.0 MPa above the fracture zone, to 0.1 MPa in the lower fragment. The bone block on both bones reduces tension in the metaphysical zones of the tibia to 2.9 MPa. Osteosynthesis of the tibia with a rotationally unstable rod during torsion leads to an increase in stress in the proximal region to 9.3 MPa, but reduces them in the diaphysis to 0.2 MPa. A rotationally stable rod reduces stress along the fracture line to 0.3 MPa. The bone block on the tibia reduces the voltage at its proximal end to 2.7 MPa. The bone block on both bones engages the tibia in the load, therefore, the zone of maximum stress passes along the line of its fracture 7.6 MPa, on the tibia, the stress along the line of the fracture decreases to 8.1 MPa. Rotationally stable torsion rod reduces stress at all control points. Conclusions. Under compression loads, rods with and without rotational stability behave identically. The use of blocks of bone grafts on both bones and only on the tibia, under the influence of compressive loads, reduces the level of stress in the bone fragments. Osteosynthesis of the tibia with a rotationally stable torsion bar reduces stress along the fracture line. When using bone graft blocks, a rotationally stable rod reduces the stress level at all control points of the model.

Keywords

• finite element method
• stress
• compression
• torsion.