| Tibia fracture is a relatively common fracture of long tubular bones. Intramedullary nail fixation is one of the main methods of surgical treatment of this fracture. Currently, interlocking intramedullary nails(IIN) used in clinical applications are mostly static fixation, which have relatively high effect of stress shielding, fatigue fracture of locking screws and other defects. This phenomenon will affect the healing of fractures, increase the suffering of patients, and hinder the development of IIN in clinical applications. Therefore, seeking a kind of IIN and locking screw that both can fix fractures reliably and have small stress concentration is a clinical problem that needs to be solved urgently. In order to solve this problem, wooden club shaped and high thread screw(WCSSHT) with IIN was designed. And it was hoped to reduce the fracture risk of locking screws effectively, achieve IIN automatically changes from static to dynamic to eliminate high effect of stress shielding, and provide a relatively good mechanics environment for fractures healing. However, the mechanical properties of WCSSHT also need a series of analyses and researches.Purpose: To study the mechanical properties of WCSSHT, verify its mechanical advantage and provide theoretical and scientific basis for its clinical application.Methods: Based on the measurement data of Chinese tibial medullary cavity, the experimental groups according to span 30 mm, 40 mm, and 50 mm are divided into A, B, C three groups. According to the actual force situation of locking screws in fracture fixed, corresponding test fixtures were designed. And test locking screws were made base on the length of span. The bending strength of WCSSHT was detected by three point bending test, and general locking screws were used as the control group. Based on the two-dimensional tomographic images of tibia that acquired by CT scan, the three-dimensional solid model of tibia was built using Mimics, Geomagic Studio software. The model of IIN, WCSSHT and general locking screws were established using Pro/E software, which assemble with three-dimensional solid tibial model respectively. They were imported into ANSYS software to construct tibial fracture models by IIN with two different locking screws. The conditions of standing by double legs, one leg, walking slowly and torsion were simulated, and the stress of tibia was analyzed by finite element method.Results: Mechanical test results showed that average maximum bending loads of WCSSHT were larger than that of general locking screws in three groups of different spans within the scope of elastic strain. Comparing with average maximum bending loads of general locking screws, those of WCSSHT improved 14.71%, 14.51%, and 23.84% respectively. Finite element analysis results showed that maximum Von Mises stress value and maxmum displacement of tibial fracture model and IIN model with WCSSHT were accordant with those of tibial fracture model and IIN model with general locking screws. And distributions of stress were similar. However, maximum Von Mises stress value and maxmum displacement of WCSSHT were smaller than those of general locking screws in different positions and stress dispersed towards two ends of locking screws.Conclusions: Bending strength of WCSSHT is larger than that of general locking screw. To WCSSHT, stress disperses towards two ends and fatigue fracture is not easy to occur. Therefore, mechanical properties of WCSSHT are superior to that of general locking screw. |
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