Biomechanical effect of external fixation system with low-modulus of elasticity on femoral shaft fracture model

Abstract

Objective To explore the effects of external fixation system with various moduli of e-lasticity on the stress and its distribution at a femoral shaft fracture. Methods Glass fiber reinforced plastic (GFRP) which resembles human femur in mechanics was used to create 8 models of femoral shaft fracture. Four models were of low elastic modulus group in which the halfpins of the external fixation system were made of titanium alloy Ti-24Nb-4Zr-7. 9Sn (E = 33 GPa) while the uther 4 were of high elastic modulus group in which the external fixation system were made of titanium alloy Ti-6A1-4V (E=110 GPa) . Strain gages were mounted near the fracture plane, halfpin and pin track to detect the stresses and their distributions under the same load in the 2 external fixation systems of different moduli of elasticity. Results The stresses at the fracture end and around the pin track increased with an increase in the load and moment. When the lateral pressure load was not less than 90 N or the bending load ranged from 1.6 N·m to 8.8 N·m, the differences in the stress at the fracture end were significant between the 2 groups (P<0.05). In 3 kinds of operating modes, the low elastic modulus group showed more symmetrical distribution and less stress concentration around the pin track. Conclusion Since external fixation system of low elasticity modulus may be better in stress transmission and distribution, it can reduce the effect of stress-shielding and accelerate bone-healing. Key words: Femoral fractures; External fixator; Biomechanics; Fractures, stress; Modulus of elasticity