title: Effects of idealized joint geometry on finite element predictions of cartilage contact stresses in the hip.
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 approximately 0.5mm). 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.
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Rm A100, Salt Lake City, UT 84108, USA. andy.anderson@utah.edu
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Anderson
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Ellis
authors.forename: Steve A
authors.initials: SA
authors.lastname: Maas
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Weiss
mesh_terms: D000818:Animals; D002356:Cartilage / Q000033:anatomy & histology / Q000502:physiology; D020342:Finite Element Analysis; D006621:Hip Joint / Q000033:anatomy & histology / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D016059:Range of Motion, Articular / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology*; D016138:Walking / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology