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Numerical and Experimental Investigation of the Effect of Cement Mantle Thickness between the Stem and the Femoral Cone in Revision Total Knee Arthroplasty

Shahjavan, Yasamin | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58360 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farahmand, Farzam; Naserkhaki, Sadegh
  7. Abstract:
  8. Revision total knee arthroplasty (rTKA) is recognized as one of the most challenging orthopedic surgeries due to extensive bone loss and compromised stability of the primary implant. The use of porous metaphyseal cones as substitutes for lost bone segments has emerged as an effective strategy to enhance implant stability. However, the optimal design of these cones—particularly the maximum allowable thickness of the cement mantle between the cone and the implant stem—has a direct impact on the biomechanical performance and long-term stability of the implant. Excessive cement thickness can lead to high shrinkage during polymerization, reduced implant-cement interface integrity, and increased micromotion, while insufficient thickness may result in inadequate fixation. Therefore, determining the optimal cement thickness is critical in clinical design. In this study, a 3D numerical model of the distal femoral structure, including the porous cone, bone cement, and implant stem, was developed in Mimics software based on medical imaging data from a real patient. Five models with varying inner cone diameters—and consequently different cement mantle thicknesses—were created. Each model was analyzed using finite element analysis (FEA) in Abaqus, incorporating both purely mechanical and thermo-mechanical simulations to account for the thermal shrinkage during cement polymerization. Boundary conditions and loading scenarios simulating daily activities such as standing were applied. To validate the numerical models, experimental tests were also conducted on physical specimens and compared with the simulation results. Key parameters investigated included stress distribution within the cement and cone, micromotion at the interfaces, and residual stresses due to thermal effects. The numerical and experimental results revealed that cement mantle thickness significantly affects the mechanical behavior and stability of the implant–cement–cone system. Thicker mantles led to stress concentration, increased micromotion, and weaker bonding, while excessively thin layers resulted in incomplete contact and suboptimal mechanical performance. A specific intermediate range of cement thickness yielded the best balance between strength, stress uniformity, and long-term stability. The study found that an average cement thickness of approximately 4.25 mm produced optimal stress profiles, with the combined thermo-mechanical stresses being lower than purely mechanical ones. Micromotion analysis further confirmed that increased thickness leads to higher wear at the interface and elevated risk of long-term loosening. The strong correlation between numerical and experimental outcomes validated the simulation approach. Although cement stress variations were not drastic, indicating that some flexibility in cement thickness may be clinically acceptable depending on anatomical needs, the study identified optimal design guidelines to improve the performance of revision knee implants
  9. Keywords:
  10. Stress Distribution ; Polymerization ; Finite Element Model ; Experimental Test ; Micromotion ; Thermomechanical Stress Analysis ; Revision Total Knee Arthroplasty (rTKA) ; Cement Thickness

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