The Effects Of The New Low Elastic Modulus β Ti Alloy On Bone Healing Of Femur Fracture In The Rat Model

Background:The internal fixation with metal implantation after fractures is still the most important and common method of surgical treatment. The high elastic modulus of rigid internal fixator can cause stress shielding, which is not good to fracture healing and rebuilding. The elastic modulus of bio-titanium alloys (Ti-6Al-4V, 110GPa) currently in use is not ideal compared with that of human bone (10～20GPa), which may lead to the obviously effects of stress shielding in the fractures. The combination of good mechanical properties and biochemical compatibility makes titanium alloys desirable implant materials for orthopedic applications. Ti-24Nb-4Zr-7.9Sn is a newβ-type titanium alloy invented recently for biomedical application. It presents higher strength (800～900MPa) than that of Ti-6Al-4V (600MPa), and with relatively low elastic modulus (33GPa).Objective:To investigate the effects of the low-modulus of elasticity fixation on fracture healing and on stress shielding by the control study of two kinds of titanium alloy with the model of rat femur fracture.Methods:The double fracture of femur of SD rats was prepared with the Utvag method. The fracture of left femur was stabilized with the high-modulus of elasticity titanium alloy pin (110 GPa) and the right with the low-modulus of elasticity (30 GPa). The bone density was showed with X-ray film. The bony calluses were observed with the micro-CT and biomechanics at four and twelve weeks after fracture. The parameters included BV,TV,BVF and ML.Results:After 4-week treatment, there was no difference of bone density between the two groups. However, there was more callus formation in the low-modulus of elasticity group than that in the high-modulus of elasticity group. After 12-week treatment, the bone density in the low-modulus of elasticity group is higher than that in the high-modulus of elasticity group. Also, there was more callus formation in the low-modulus of elasticity group.After 4-week treatment, in ROI1, TV in the low-modulus of elasticity group was higher than that in the high-modulus of elasticity group and BVF was lower, while there was no difference of BV between two groups; in ROI2, there was no difference between the two groups on BV,BVF and ML. After 12-week treatment, in ROI1, BV, BVF and TV in the low-modulus of elasticity group were all higher than in the high-modulus of elasticity group; in ROI2, BV,BVF and ML in the low-modulus of elasticity group were all higher than in the high-modulus of elasticity group. After 4-week treatment, there was no obvious difference of bony callus form or diaphysis caliber between the low-modulus of elasticity group and the high-modulus of elasticity group. After 12-week treatment, the bony callus form and diaphysis caliber of the low-modulus of elasticity group were better than those of the high-modulus of elasticity group. Histomorphology showed that there was more bone trabeculae in the low-modulus of elasticity group than in the high-modulus of elasticity group after 4-week treatment. Also, after 12-week treatment, there was more collagen and bony callus form, bone trabeculae was thicker, and lamellar bone arrayed more regularly in the low-modulus of elasticity group.Conclusions:The new low elastic modulusβTi alloy is in advantage of building the bony calluses after fracture, decreasing the loss of bone mass, improving the quality of bone healing, and finishing the repair of fracture, therefore, it is a promising interplantation of fracture in the future clinical application.