A Photoelastic Study of Contact Stress on the Tibial Insert of Knee Prosthesis at Deep Flexion

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This paper presents the experimental results of photoelasticity for determining the magnitude and distributions of stresses on the polyethylene insert of typical three types of posterior stabilized knee prostheses designed to attain high/deep knee flexion. Three prostheses used in the experiment were a conventional posterior stabilizer knee, Scorpio NRG (Stryker Co., USA), Bi-surface knee (Kyocera Inc., Japan) with a unique design with a ball-and-socket joint and CFK (Complete Flexion Knee, Japan Medical Material Co., Japan) which we have developed by further improving the Bi-surface so as to make a complete knee flexion. Epoxy resins were selected to fabricate the tibial insert models. Special equipment was used to apply 2 kg force on the model by setting knee flexion angle at 0°, 30°, 60°, 90° and 120° respectively. After that, the stressed model was sliced in parallel with the sagittal plane and photoelastic fringes in each slice were observed. The results demonstrated that while knee angle was smaller than 90°, shear stress on the lateral slice became highest for Bi-surface, followed CFK and NRG was lowest, indicating NRG has high conformity as to the condylar insert articulation. After knee angle bacame larger than 90°, shear stress on the mid-posterior slice became highest for NRG, followed Bi-surface and CFK was lowest. We may conclude that CFK has optimal configuration at deep knee flexion from a load bearing viewpoint.
2008-09-30