N.Chandran, F.Amirouche PhD, M.Gonzalez MD
Total Knee Arthroplasty is the final solution to the arthritis of knee after all medication fails to relieve pain. The success rate of the surgery is very high. But still there are a considerable number of pre-mature failure cases of TKA. Several studies attribute the failure to polyethylene wear of the tibial component.
A posterior stabilizer on the tibial component is to enforce posterior roll back of the femoral component on the tibial surface and to prevent posterior subluxation. But dislocation and extra bone resection make this option less than ideal. The stabilizing post of the polyethylene component permits femoral rollback after 70 degree flexion. The rollback is due to the slope and curvature of the posterior part of the stabilizing post which makes contact with the femoral component at 70 degree.
FEM Model of Total Knee Arthoplasty
Aim and Objective
The main objective is to study the distribution of the contact pressure on the condylar surfaces of the polyethylene component as a function of flexion-extension angle with experimental studies and computation studies with FEM.
Objective of the study is to optimize the design of the stabilizing post and to understand the mechanism of rollback.To study the stress distribution on the posterior face of the stabilizing post. In order to study the influence of the geometric parameters of the tibial post that influence the femoral rollback mechanism different designs of the PS tibial component are considered with varying geometric parameters of the stabilizing post
Arthroplasty as a Function of Component Position and Ligament Balance Using Both Experimentally Recorded Data and Finite Element Modeling.
Improper alignment or balancing of the total knee arthroplasty can produce peak pressures that will cause accelerated wear or premature failure of the bone prosthesis interface. In this study, contact pressures inside cadaver knee joints are recorded using thin (0.005") pressure sensors that are built into a special tibial insert. The knee is placed through a range of motion and the contact pressure is recorded in real time. Pressure readings are correlated with component position and ligamentous balance allowing optimization of these parameters. Finite Element Modeling (FEM) and Gait Analysis is then used to correlate the contact pressure distribution with the degree and direction of malrotation.
Validation of Contact Pressure for Depuy Posterior Stabilizer using Finite Element Model of the Total Knee Arthroplasty
3D FEM model of the PCL substituting TKA with all its components is developed. This includes the distal portion of the femur, the proximal portion of the tibia, and non-linear spring like model of the quadriceps and collateral ligaments. Consideration of the strain effect of ligaments during flexion-extension motion makes the model a more accurate representation of the TKA. A quasi-static simulation of the knee was performed at different flexion-extension angles. The tibio-femoral interface contact stresses were computed. The stress values were validated with the experimental results of contact stress obtained in experiment using pressure sensors embedded in the polyethylene component. The experiment was performed on a cadaver knee with TKA and the thin film pressure sensors were glued in between the articulating surfaces. The penetration of the femoral component in to the polyethylene component of the knee as a function of increasing load is studied. The friction between the articulating condyles and the sliding of the contact points due to the friction are validated with this model. Validation with FEM makes the model suitable for misalignment and instability studies of the TKA. The quadriceps and ligaments deformation in maintaining stability of the knee was seen to be more pronounced when the flexion angle increases.
Simulation of contact analysis for total knee replacement in FEM
Effect of Slope Changes in Posterior Stabilizer on the Rollback Mechanism of the Knee in Flexion-Extension
The posterior stabilizer is said to have more femoral rollback than the standard tibial component with the Posterior cruciate ligament sacrificed. In addition statistically the posterior stabilizer is better than PCL retaining TKA. A posterior stabilizer role on TKA is to enforce posterior roll back of the femoral component on the tibial surface and to prevent posterior subluxation of the tibia. Femoral cam engages with the tibial post at high flexion angle. The articulation of the femoral cam with the tibial post is studied through finite element method to describe the rollback mechanism and the posterior displacement of the femoral contact points in the condylar surfaces are compared for different designs to asses the rollback and nominal stress condition on the cam surface.
Simulation of femoral rollback mechanism
F. Amirouche, M. Gonzalez, L. Arum “A Contact Pressure Based Prosthetic Fitting Device For a Total Knee Arthoplasty (TKA)” Journal of Prosthetics and Orthotics (In review)
F.M.L., Amirouche, M. Gonzalez, et al, “ Sensitivity and error analysis in conjunction with Tibial Intramedulllary Guides in Total Knee Arthoplasty” Journal of Arthoplasty.00.023 (in review)
F.M.L., Amirouche, M. Gonzalez, et al.“Geometrical Analysis of Potential Error in using Femoral Intramedullary Guides in Total Knee Arthoplasty.” Journal of Arthoplasty.98.227.to appear December 2000
Nagarajan Chandran (1), Dr.F.M.L.Amirouche (1) Effect of Malalignment and friction on contact pressure in the polyehtylene component of the TKR ASME – Bioengineering Division – 2002
Amirouche F, Aram L, Gonzalez M, Giachetti R, Mahr C. "A Contact Pressure Based Prosthetic Fitting Device for a Total Knee Arthroplasty" Proceedings of the Engineering of Sport. June 2000
Amirouche F, Aram L, Gonzalez M, Giachetti R, Mahr C. "The Fitting of the Human Joint Through Micro Implanted Sensors" Proceedings of the 1st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine & Biology. Oct 2000
Giachetti R, Amirouche F, Aram L, Gonzalez M. "Biomechanical Problems with Contact Pressure Distribution in the Knee Joint after Total Knee Arthroplasty" Proceedings of the ASME Winter Conference. Nov 200
Amirouche F, Giachetti R, Aram L, Gonzalez M. "Induced Stress in TKA Resulting from Malrotation" Proceedings of the ASME Bioengineering Conference. June 2001
Amirouche F, Giachetti R, Aram L, Gonzalez M. "Validation of a Finite Element Contact Model for the Use in Total Knee Arthroplasty" Proceedings of the International Society of Biomechanics. July 2001
Aram L, Amirouche F, Gonzalez M, Giachetti R. "Characterization of Contact Pressure in Total Knee Arthroplasty as a Function of Component Position and Ligament Balance" Proceedings of the International Society of Biomechanics. July 2001
Nagarajan Chandran (1), Dr.F.M.L.Amirouche (1) Effect of Slope Changes in Posterior Stabilizer on the Rollback Mechanism of the Knee in Flexion-Extension ASME – Bioengineering Summer Conference 2003(Submitted).