Effects of idealized joint geometry on finite element predictions of cartilage contact stresses in the hip

• Published in: Journal of biomechanics Vol. 43; no. 7; pp. 1351 - 1357
• Main Authors: Anderson, Andrew E., Ellis, Benjamin J., Maas, Steve A., Weiss, Jeffrey A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 07.05.2010; Elsevier; Elsevier Limited
• Subjects: Animals; Biological and medical sciences; Biomechanics; Biomechanics. Biorheology; Boundary conditions; Cartilage; Cartilage - anatomy & histology; Cartilage - physiology; Cartilage pressures; Conchoid; Finite element; Finite Element Analysis; Fundamental and applied biological sciences. Psychology; Hip; Hip joint; Hip Joint - anatomy & histology; Hip Joint - physiology; Humans; Models, Biological; Physical Medicine and Rehabilitation; Range of Motion, Articular - physiology; Skeleton and joints; Sphere; Stress, Physiological - physiology; Studies; Tissues, organs and organisms biophysics; Vertebrates: osteoarticular system, musculoskeletal system; Walking - physiology; Weight-Bearing - physiology; Biomechanics; Sphere; Conchoid; Boundary conditions; Cartilage pressures; Hip; Finite element; Human; Shape; Joint; Modeling; Osteoarticular system; Finite element method; Articular cartilage; Contact stress; Morphology; Surface properties; Physiology; Biomedical engineering
• ISSN: 0021-9290; 1873-2380; 1873-2380
• DOI: 10.1016/j.jbiomech.2010.01.010

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.