Oblique Impact On The Medial Femoral Locking Plate Fixed Biomechanics

Objective The use of technology in the treatment of femoral shaft MIPO comminuted fracture, due to the anatomy exposed inadequate, resulting in increased difficulty to adjust the plate position. There are three stress experiment to test the premise of ensuring that all the screws are to penetrate the cortical bone of the lower bunk, oblique locking plate and upright locking influence on the mechanical properties of steel fracture strain, steel strain strength of the fixed model for clinical application provide a theoretical basis.Methods Select the40generic models and artificial femoral mechanical properties similar to human femur were randomly divided into A, B, C, D four groups,10in each group, in the lesser trochanter of the femur transverse osteotomy at15cm and17cm,2cm long cylinder made type of bone, bone trimming back the defect after femur comminuted fracture simulation model. After12holes were locking plate and cortical bone screws, A group using standard AO techniques fixed, that being the mid-point of the fracture center steel, steel plate placed in the middle of the longitudinal axis of the femur; B steel plate placed in the femoral axis5degrees the angle between the axis; plate placed in group C with10degrees to the longitudinal axis of the femur, d group plate is placed into the femoral angle of15degrees to the longitudinal axis. After fixing the measuring four groups in axial compression, three-point bending, axial torsion test local strain of the steel surface, the lateral strain fracture fragments, as well as the maximum bending strength model, the maximum compressive strength and maximum torsional strength. All data using SAS software for single-factor analysis of variance to determine the mechanical properties of the four groups of fixation methods.Result In different compression load stress, A, B, C, D of four inclined plates with increasing angle, d, e points of strain variation was not statistically different. In the stress under load500N, d fracture strain point between4-5%, and the strain point e between1-2%. Under1200N load stress and strain between7-8%d point, strain e point between2-3. Under1800N load stress and strain d point between9-11%strain e point between4-5%. Bending load under different stresses, A, B, C, D of four inclined plates with increasing angle, d, e points of strain variation was not statistically different. In the stress under load200N, d fracture strain point between4-5%, and the strain point e between1-2%. D strain point between7-9%, e between the strain point of2-3at a load of500N stress. D point under strain1000N load between11-13%of stress, strain e point between5-6%. In smaller torsional stress load (ION· m, and20N·m), A, B, C, D with four inclined plate angle increases, d, e strain variation points having no significant difference. In10N· m under load stress, de point of fracture strain between3-4%. In the20N·m of load stress strain de between7-8points. In larger torsional loads (50N· m) de strain point between9-24%, the steel sheet that is the rotation angle of more than10℃group, the instability of the screw on both sides of the steel sheet, resulting in significantly increased suddenly fracture strain, a significant difference.Under1800N compressive load, strain a point of steel decreases, strain b, c point increase, this difference was statistically significant (P<0.05). In500N bending load, strain a point of steel decreases, strain b, c point increase this difference was statistically significant (P<0.05). In the20N· m torsional load, strain a point of steel decreases, strain b, c point increase this difference was statistically significant (P<0.05) this difference was statistically significant.When under axial compression load, strain medial fracture fragment greater than10%, the experiment is stopped. A, B, C, D into four groups with the inclined angle increased, the change in the fixing strength of the model was not statistically significant. When under bending load, strain medial fracture fragment greater than10%, the experiment is stopped. A, B, C, D into four groups with the inclined angle increased, the change in the fixing strength of the model was not statistically significant. Under torsional loading, A group was105.35±6.18in intensity when the fracture strain of>10%, group B strain fracture occurs>10%of the required strength of107.12±5.24, group C torsional strength of85.74±8.05MPa when two plates end of screw breakage, D groups due to the weak side of the bone screws, screw breakage before, first cut out the cortical bone strength as56.25±6.53MPa. P <0.05was statistically significant.Conclusion Oblique axial compression plate model anti-impact strength and resistance to mechanical bending strength generated was not statistically significant, but greater than10degrees inclined plate model significantly reduced anti-torsional strength. Also prompted when fully weight-bearing exercise, more than10degrees inclined plate fracture strain will significantly increase, easily lead to nonunion. These conclusions prompted in clinical practice, the use of MIPO technical treatment of femoral shaft comminuted fractures, not the pursuit of the perfect imaging and constantly adjust the placement angle steel, these operations further damage tissue and soft tissue damage to the blood supply, prolonged operative time, increased medical staff C-shaped wall at the time of exposure, but this should be within a certain angular range of more than10degrees oblique fracture fixation plate will significantly reduce the torsional strength.