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 interface between bone/cartilage. 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.

Finite Element Analysis Examining the Effects of Cam FAI on Hip Joint Mechanical Loading Using Subject-Specific Geometries during Standing and Maximum Squat

“…Using the subject-specific kinematics data, the femur was oriented with respect to the pelvis according to the squat interval. The X-Y-Z-axis corresponds with the left hip's lateral-posterior-superior directions neglected [1,2,9,38], the peak stresses in our FEA were not situated on the cartilage, but instead were located on the underlying bone of the acetabulum [37,43]. These peaks could have been due to the lower elastic modulus of the cartilage layer.…”

Using a Finite Element Pediatric Hip Model in Clinical Evaluation - A Feasibility Study

“…In general, the thicker cartilage revealed a larger area in contact, but also a higher peak pressure. Kim et al constructed a FE model of the pelvis of a 10-year old child and used an experimental study to adjust the material properties from an adult's to a child's [25]. Their updated bone material properties were in accordance with the findings by Currey and Butler [28].…”

“…Unfortunately, they did not evaluate their model against a FE model with elastic bones despite Anderson et al demonstrated that assuming rigid bones might alter cartilage contact stresses in the hip joint [7]. Anderson et al investigated the impact of several common simplifications in FE models [25]. Using a model with subject-specific bone geometry, cartilage thickness, and bone material properties as the gold standard, they found models with constant cartilage thickness to overestimate contact cartilage pressure and underestimate contact area.…”

Assessment of stress distribution in ankle joint: simultaneous application of experimental and finite element methods

“…In the computational model, bones keep their relations on the neutral position of the foot, the same as its situation at imaging time. Each bone was defined as a flexible body in the software (Anderson et al, 2010). In this study, quasi-physiologic loading parameters including periodic loading, as well as time-dependent and viscoelastic properties have not been considered (Anderson et al, 2007;Chegini et al, 2009).…”