The Biomechanical Properties Analysis Of Tibial Cross Section In Total Knee Arthroplasty With Different Osteotomy Tickness

ObjectiveIn the field of joint surgery, Total Knee Arthroplasty(TKA) has become a commonly method for the treatment of knee joint diseases, especially for the patients with advanced severe lesions. Patients can relieve pain, restore function and improve the quality of life after total knee replacement. According to the severity of the disease, soft tissue balance, flexion extension gap balance,doctors experience and so on to determine thickness of tibial osteotomy in TKA. Therefore, osteotomy thickness is difference about 4mm. Previous studies have indicated that the strength of the articular surface is different with the distance of the tibial plateau. Prosthesis loosening and sinking is related to the cross section strength of the tibia, the biomechanics between the tibia and the prosthesis, soft tissue and postoperative activities, and the loosening and sinking of the prosthesis directly affects the life of the prosthesis and the long-term effect of the operation. Thus obtain biomechanics of tibial sections under the condition of different osteotomy thickness and different activities and study of biomechanical changes of tibial osteotomy plane to provide theoretical basis for the clinical knee arthroplasty resection of bone thickness and lengthening prosthesis life.Methods1 Data acquisition and 3D reconstructionWe selected 7 cases of normal young volunteers, 2 males and 5 females, aged 23-26 years old, with no history of lower extremity joint diseases and injuries and scanned their left lower limb by CT, storaged data with DICOM3.0 format, imported into 3D reconstruction software mimics 10.0 and reconstructed left lower limb bone three-dimensional model by marking orientation, setting thresholding, region growing, creating polyline, fill the empty and so on.2 Simulated surgical osteotomyThe three-dimensional model of lower limb bone was imported into the reverse engineering software Geomagic Studio12.0 to find out the center of the knee joint, the center of the ankle joint, tibial mechanical axis and the datum plane of tibial osteotomy. Then on the base of datum plane, we made osteotomy along the tibial mechanical axis with the thickness of 5mm, 7mm and 9mm respectively.3 Proximal tibial material propertiesThe tibia model after ostetomy has respectively imported to 3D reconstruction software mimics and finite element analysis software Ansys, made the model surface meshing and body meshing, then write PREP7 files, nodes files and elements file for backup. We assign model of 10 kinds of materials using the uniform assignment in Mimics.4 Biomechanical analysis of tibiaThe model with assignment materials were reimport into the ANSYS and made finite element analysis by restraining freedom degrees, applying load,solution and so on. Our studies made biomechanical analysis of the single knee joint force under different living conditions.Results1 Three dimensional bony model of lower limb was successfully reconstructed, the model was clear and vivid, and the bone markers and morphology of the lower limb could be truly reacted; the proximal tibia was osteotomed in different thickness by simulating total knee arthroplasty.2 10 kinds of material properties were assigned successfully to the tibial model, which could be better reflect to the biomechanical properties of the tibia.3 The finite element analysis results of tibial osteotomy surface showed that the stress and displacement of the tibial osteotomy surface increased with the increase of the thickness of the osteotomy in the same active state. And in the same section of bone thickness, with enhanced active state, maximum stress and displacement of tibia section was increasing. It is worth noting that the displacement and stress of tibial osteotomy surface in the condition of osteotoming 9mm and upstairs state reached the maximum.ConclusionIn the total knee arthroplasty, with the increase of the thickness of the tibial osteotomy, the stress and strain of the cross section is also increased. And the increase of postoperative activity of the knee joint can also increase the stress and strain of the tibial section. Therefore, in the operation,we should avoid excessive osteotomy, and patience should avoid high intensity activities postoperative, in order to reduce the stress and strain of the tibial plateau, which is conducive to the long-term life of the prosthesis.