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Computer model to predict subsurface damage in tibial inserts of total knees
1Centre for Biomedical Engineering, University College London Medical School, Royal National Orthopaedic Hospital Trust, Stanmore, Middlesex, England. 101360.2721@compuserve.com
Summary
This study analyzed total knee replacement designs to predict delamination in ultra-high molecular weight polyethylene tibial inserts. A superior design showed significantly lower damage scores due to optimized geometry and motion, suggesting improved fatigue life.
Area of Science:
- Biomedical Engineering
- Materials Science
- Orthopedic Surgery
Background:
- Delamination of ultra-high molecular weight polyethylene (UHMWPE) tibial inserts is a failure mode in total knee replacements (TKRs).
- Understanding the influence of bearing surface geometry on UHMWPE susceptibility to delamination is crucial for improving TKR longevity.
Purpose of the Study:
- To analyze two TKR designs and assess how bearing surface geometry impacts UHMWPE insert delamination.
- To develop and apply a novel damage function simulating gait mechanics for predicting fatigue failure.
Main Methods:
- Rigid body analysis calculated femoral component orientations on tibial surfaces during the stance phase of gait.
- Finite element analysis (FEA) simulated component compression to determine stresses within UHMWPE tibial inserts.
- A novel damage function, analogous to strain energy density, quantified accumulated stress cycles to predict fatigue failure.
Main Results:
- One TKR design exhibited a damage score over three times lower than the other.
- The superior design featured lower stresses and more complex contact point movement (medial-lateral and anterior-posterior) during internal-external rotation.
- Geometric factors, including large outer frontal radii and frontal plane conformity, were associated with the reduced damage score.
Conclusions:
- The proposed FEA-based method, incorporating gait motion and stress, offers a more realistic prediction of delamination susceptibility compared to static tests.
- TKR designs with specific geometric characteristics, such as large outer frontal radii and frontal plane conformity, may reduce the risk of UHMWPE insert delamination.