Research On Biomechanics In The Stability Of Intramedullary Nail Fixation For Lower Limb Bone Fracture

Intramedullary nail is a traditional surgical method to fix human lower limb fracture.However,the micro-motion between intramedullary nail and bone face is an important aspect to influence the fracture healing.Micro-motion have a great influence on the callus formation of fracture site,thus the micro-motion control of fracture site has been one of the most important intervention factors in the fracture treatment.Previous studies have found that the stability maintenance of intramedullary nail was not very good,and intramedullary nail fixation system was inclined to generate torsion and shear stress on the fracture sites,causing the deformation of fracture site,which was not good for the formation of callus on the fracture site.In order to resolve the problem,two femur fixation systems and two tibia fixation systems were constructed.For the femur fixation system,we tried to compare the traditional intramedullary nail fixation with the one fixed both by intramedullary nail and plate-screw from the point of stress and displacement.For the tibia fixation system,we made a comparison between the tibia fixed only by intramedullary nail and the one fixed both by intramedullary nail and blocking screws according to the stress and displacement distribution.We analyzed whether or not the plate fixation in femur and blocking screws fixation in tibia would improve the stress shielding.By comparison the displacement changes both in femur fixation and tibia fixation,we have illuminated the roles of plate and the blocking screws in the control of micro-motion in fracture site for its respective fixation model.This study focuses on the influences of femur plate and tibia locking screws on the micro-motion of fracture site.According to the analysis result,femur fixed both by intramedullary nail and plate suffers from a lower stress,reduced by around 38.9%,59% compared with femur fixed by intramedullary nail only for the axial load and rotating loads respectively.From the view of stress shielding,the stress shielding rate for femur-intramedullary nail-plate fixation system is lower than femur-intramedullary nail fixation system both for the axial load and rotating loads.Under the force of axial load,there is no distinct difference between the tibia-intramedullary nail fixation system and tibia-blocking screw fixation system,both of them ranging from 40% to 50%.However,things are different for the tibia under the load of torque.The stress shielding rate in the middle tibia is around 46% for the tibia fixed by intramedullary nail only.While,the stress shielding rate is 17% for the tibia fixed both by intramedullary nail and blocking screw.Our researches can provide the theoretical references for the clinical practice on the field of intramedullary nail fixation in the treatment of both femur and tibia facture.