Press-fit fixation and viscoelastic response of a bone-implant interface in the distal femur.

摘要

Implant loosening is a primary concern for individuals receiving primary total knee arthroplasty. To investigate this concern, femoral knee components were implanted in vitro on three cadaveric femurs. The press-fit fixation was measured using strain gauged femoral components immediately after implantation and for 10-25 minutes after implantation. Specimen-specific bone-implant finite element (FE) models were created to predict the initial fixation of the interface of each femur. The FE models were calibrated using the in vitro strain measurements and used to assess initial fixation.;The initial fixation was demonstrated experimentally by the minimum principal strain at the strain rosette locations. The FE models were used to calculate the stress distribution and pressure maps of the interface surfaces of each bone. The initial fixation and pressure on the internal surfaces of the implant were shown to increase with bone density. The FE models showed that the geometry of the implant causes the distal femur to deform plastically with more bone on the lateral side plastically deforming than the medial side. The geometry causes higher stresses in the lateral side as well as higher pressures on the lateral surfaces. The implementation of plasticity in the material model for bone in the FE model decreased these strains and pressures considerably from a purely elastic model, which demonstrated the importance of including plasticity. The fixation of the femoral component was found to decrease in time due to the viscoelastic behavior of cancellous bone. The time-dependent response of the in vitro implantation was compared to a post-yield viscoelastic relaxation experiment performed on bovine cancellous bone.;Quasi-static compression experiments on cancellous bone samples from the distal femur were performed to determine the relationship between mechanical properties and density in the anterior-posterior direction. The bone mineral apparent density (BMAD), apparent modulus of elasticity, yield and ultimate stress, and yield and ultimate strain were measured for twenty-eight cylindrical specimens. The mechanical properties each significantly differed (p 0.05) in the superior and inferior locations and linear and power law relationships between the superior and inferior mechanical properties and BMAD were determined.