Biomechanical Study Of Arthroplasty For Osteoporosis Unstable Intertrochanteric Fractures

Background: Intertrochanteric fractures are common in the elderly osteoporotic fracture, of which about 35% -40% is unstable. With the rising awareness of such fractures, reducing complications by early surgery has reached consensus for most surgeons; various fixation methods used in clinical for the stable intertrochanteric fractures have received good results, contrary to the high failure rate for unstable intertrochanteric fracture combined with osteoporosis in elderly patients,which takes a long time in bed for healing after the internal fixation, and has a higher incidence of complications; in recent years, arthroplasty in the treatment of intertrochanteric unstable fractures has achieved better results; patients can get out of bed after surgery to reduce and avoid complications. Currently the researches of the unstable intertrochanteric femoral fractures has focused on clinical research, with few biomechanical studies and most of which focus on the ordinary mechanical tests. Ordinary mechanical tests can not be directly applied to humans, and could only measure part of the mechanical parameters among all the points, with low comparability between models; with the rapid development of the computer technology and the concept of the digital orthopedic, orthopedic biomechanics get into the digital age ; three-dimensional finite element analysis is an important method for biomechanical research, analyzing joint, spinal and other bio-mechanical problems, and effective method of human biomechanical study.Object: Computer simulation of arthroplasty for unstable intertrochanteric fractures combined with Osteoporosis, and analysis the femur and prosthesis-related stress distribution, evaluate the initial stability of the prosthesis after surgery; provides theory foundation for the choice of prosthesis and the reconstruction of proximal femur fractures.Methods: The data of femur osteoporosis of the volunteers were obtained by means of spiral CT scanning; The graphical data is processed by the mimics11.1(a graph processing software), then outline curve data of the femur bone cortex, inside surface and outside surface were obtained; The curve data is imported into the Unigraphic NX4.0(name of a software), solid modeling is performed, the three-dimensional model of femur composed of the bone cortex ,spongy bone and marrow cavity is obtained; three-dimensional modeling was performed in the modeling software UG4 .0,based on AML biological prosthesis from Deputy company and the Smith & Nephew Muller cemented prosthesis,and the digital data of normal shank, A, plus long-handled B, solution handles C, normal shank D were obtained and the three-dimensional digital models were inserted into the normal femoral neck osteotomy and intertrochanteric femoral fractures femur respectively in UG4.0 modeling software to simulate artificial femoral head replacement surgery, and to form the model group 1 (A1, A2), group 2 (B1, B2), group 3 (C1, C2), Group 4 (D1, D2); the model were imported into the finite element analysis software ansys11. 0 for tetrahedral mesh, and refinement treatment were done to the proximal femoral mesh,material assignment, the definition of contact force loading, stress analysis were carried out according to related references.Results:1 established three-dimensional finite element model of osteoporosis femur prosthesis, joint replacement surgery.2 the stress of the Lesser proximal femur decreased obviously after the arthroplasty, the stress of the calcar femorale declined most significantly. And the stress concentrated on femoral condyle, shifted to distal femur compare with preoperative; the stress of the femur of distal prosthesis increased significantly; the maximum stress on the femur compared with preoperative increased. Proximal femur had lower stress. Comparison of normal joint replacement group (control group) and the intertrochanteric fracture of artificial joint replacement (experimental group) showed similar stress trend of the entire femur, and the joint force conducted through the metal prosthesis to the distal femur. Experimental group suffers less stress on the proximal femur than the control group, and the maximum stress on the femur increases. Shank prosthesis has similar stress trend on the distal femur compared with the short shank prosthesis, the length of the prosthesis affects little over the stress trend of the distal femur. Biological prosthesis and bone cement prosthesis have consistent effects on the femur stress trend; bone cement prosthesis experimental group and control groups have similar trends in femur stress.3 prosthesis stress transfer from the top down, mainly concentrated on the tight binding isthmus of the prosthesis and the bone marrow cavity, terminal warheads of the prosthesis has no contact with the bone and therefore suffers little stress. The middle and distal part of the prosthesis passes the stress of the femur. Prosthesis maximum stress, is greater than the femur. Handle length of prosthesis does not change the trend of the force, the stress is mainly concentrated in the closely contacted part of the prosthesis and the bone marrow cavity.Conclusion: artificial hip joint replacement changed the stress attribution of the femur. the stability of intertrochanteric fracture after joint replacement prosthesis is acceptable, and joint replacement does not tend to fail under normal load. femoral isthmus is complete, and the length of prostheses has little effects to the stress attribution of femur after replacement 4 the immediate stability provided by bone cement, combined with the stability reconstruction of top wire fixation of intertrochanteric fractures,the experimental group and control group femur showed similar stress attribution.