Effects of idealized joint geometry on finite element predictions of cartilage contact stresses in the hip |
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| Authors: | Andrew E Anderson Benjamin J Ellis Steve A Maas Jeffrey A Weiss |
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| Institution: | 1. Department of Orthopaedics, University of Utah, 590 Wakara Way, Rm A100, Salt Lake City, UT 84108, USA;2. Department of Bioengineering & Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT, USA;1. Department of Mechanical and Aerospace Engineering, Carleton University, 3135 Mackenzie, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6;2. Division of Orthopaedic Surgery, Ottawa Hospital, Ottawa, Canada;3. Institute for Biomechanics, ETH Zurich, Zurich, Switzerland;1. Health Sciences and Technologies, Interdepartmental Center for Industrial Research (HST-ICIR), Alma Mater Studiorum—University of Bologna, Bologna, Italy;2. Center for Biomedical Engineering, Brown University, Providence, RI, USA;3. Department of Industrial Engineering (DIN), Alma Mater Studiorum—University of Bologna, Bologna, Italy;4. Department of Orthopaedics, Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, RI, USA;1. Université de Franche-Comté, 25000 Besançon, France;2. FEMTO-ST Institute, Department of Applied Mechanics, UMR CNRS 6174, 24 rue de l''Epitaphe, 25000 Besançon, France;1. Center for Biomedical Engineering and School of Engineering, Brown University, Providence, RI 02912, USA;2. Department of Orthopaedics, The Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, RI 02903, USA;3. Department of Computer Science, Brown University, Providence, RI 02912, USA;4. Robert A. Chase Hand & Upper Limb Center, Department of Orthopaedic Surgery, Stanford University, Stanford, CA 94304, USA |
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| Abstract: | Computational models may have the ability to quantify the relationship between hip morphology, cartilage mechanics and osteoarthritis. Most models have assumed the hip joint to be a perfect ball and socket joint and have neglected deformation at the bone-cartilage interface. The objective of this study was to analyze finite element (FE) models of hip cartilage mechanics with varying degrees of simplified geometry and a model with a rigid bone material assumption to elucidate the effects on predictions of cartilage stress. A previously validated subject-specific FE model of a cadaveric hip joint was used as the basis for the models. Geometry for the bone-cartilage interface was either: (1) subject-specific (i.e. irregular), (2) spherical, or (3) a rotational conchoid. Cartilage was assigned either a varying (irregular) or constant thickness (smoothed). Loading conditions simulated walking, stair-climbing and descending stairs. FE predictions of contact stress for the simplified models were compared with predictions from the subject-specific model. Both spheres and conchoids provided a good approximation of native hip joint geometry (average fitting error ～0.5 mm). However, models with spherical/conchoid bone geometry and smoothed articulating cartilage surfaces grossly underestimated peak and average contact pressures (50% and 25% lower, respectively) and overestimated contact area when compared to the subject-specific FE model. Models incorporating subject-specific bone geometry with smoothed articulating cartilage also underestimated pressures and predicted evenly distributed patterns of contact. The model with rigid bones predicted much higher pressures than the subject-specific model with deformable bones. The results demonstrate that simplifications to the geometry of the bone-cartilage interface, cartilage surface and bone material properties can have a dramatic effect on the predicted magnitude and distribution of cartilage contact pressures in the hip joint. |
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