THE COMPUTER MODELING STUDY OF INTERACTIONS BETWEEN CONTACT SURFACES OF METAL OR POLIMERIC SCREWS AND CORTICAL BONE TISSUE

The continuous growth of fracture rates and surgeries with the use of screws requires modern approaches to improve treatment results. The interaction between a screw and bone tissue is one of the critical factors that affects the stability of a fracture and remains not thoroughly researched until now. The computer modeling method allows for studying precisely the strains and deformities in the contact areas of metal screws, polymeric screws, and cortical bone.Material and methods. The computer modeling was performed in Autodesk Fusion 360 for biomechanical interactions of 3.5 mm AO screws made of stainless steel and polyamide-12 (P-12) with monocortical diaphyseal part of long tubular bone. The static stress study was performed for different loads applied in the pull-out direction with the bonded contact used between the screw and the bone. The displacement and strains were revealed in different parts of the screw thread and surrounding bone tissue for the force applied along the screw axis in the range from 100 N to 1000 N.Results. The increase of the force resulted in stress and strains in the screw and surrounding bone tissue, and the maximum force values can lead to unstable fixation. It was determined that polymeric P-12 screws in all study cases were affecting the bone with less contact pressure than metal screws. In the superficial bone areas this difference was more significant – 24.8 %, and in the deep bone areas it was 8.9 %. The areas of von Mises stress in both superficial and deep parts of polymeric screws were in the range from 1.414 MPa to 20.74 MPa which was lower than that of metal screws (3.484 MPa to 56.24 MPa).Conclusions. Polymeric P-12 screws will fix bone fractures better under low intensive but long-lasting loads, as their destructive effect on bone tissue around screws will be less than of metal ones. On the other hand, metal screws will have the advantage to resist the short lasting but intensive “peak” loads. The less stress areas in the polymeric screw can somehow compensate the lower mechanical strength parameters of P-12 material.Perspective of further research. The obtained results can be taken into account during orthopedics surgeries when screws are used for fixation, as well as for further biomechanical studies.