Study On The Biomechanical Properties Of Internal Fixation Metal Plate Of Femur Shaft Fractures

With the improvement of biological fixation,locking compression plate(LCP)has been widely used for the internal fixation of fractures.A certain extent of micro-movement at the fracture site is allowable for biological fixation(also called flexible fixation),although the rigid internal fixation generally emphasizes on anatomical reduction.The micro-movement promotes the formation of callus to induce indirect or secondary fracture healing.Indirect fracture healing is very sensitive to the mechanical environment of fracture sites,and inadequate stress may lead to delayed union,non-union or other complications.The stability of internal fixation plays an important role in the mechanical environment of fracture sites,and it is influenced by such factors as design parameter of bone plate,mechanical properties and the configurations of bone plate in the clinic surgery.Therefore,it is very necessary to investigate the influences of these factors on internal fixation system from the perspective of fracture healing,which may provide some valuable insights into the improvement of clinical operation and the optimal design of bone plate.In this study,a finite element model of internal fixation system in the central transverse of femoral shaft was established firstly,and then numerical simulation of the time-varying process of facture healing in the early stage was conducted by means of the theory of interfragmentary strain.Particular attention was paid to the influences of the number of screw,the fixed position and pre-tightening force of screw and the material and length of bone plate.Moreover,the matching relation between the size of fracture gap and the material and length of bone plate was analysed.The main results and conclusions are drawn as follows:1.The screw pre-tightening force has no significant effect on the development of callus,the stress distribution of the femur and the plate during the process of fracture healing,but the maximum stress at the screw hole of the femur increased with the increase of the screw pre-tightening force.At least three screws should be implanted into the fracture interfragmentary for each side of fracture line when 8-hole locking compression plate was used to fix femoral shaft fracture.The two screws close to the fracture line contributed significantly to the healing of fracture and thus they must be implanted.2.In terms of the performance of internal fixation,there existed a negative correlation between the gap size of fracture and the elastic modulus of bone plate.The best fracture gap of stainless steel plate,pure titanium plate,and magnesium alloy plate was 1-2 mm,2-3 mm,and 4-5 mm,respectively.For each bone plate,long bone plate should be more suitable to large fracture gap so as to obtain sufficient fixation stability at the later stage of fracture healing.3.In the early stage of fracture healing,the stress shielding rate was higher for stainless steel plate,pure titanium plate and magnesium alloy plate,and there were no significant differences among them.The material properties of metal bone plate could affect its stress shielding rate by influencing the elastic modulus of callus.