4th Annual Mountain West
Biomedical Engineering Conference

Intra-articular stresses, including contact stresses, play an important role in cartilage health within the hip joint. We have shown that a subject-specific finite element (FE) model can predict cartilage contact stresses in agreement with in-vitro data. The objective of the current study was to quantify the magnitude and spatial distribution of contact stresses in normal human hips, using our validated FE protocol. Three-dimensional reconstructions were made from CT images of five healthy subjects. Cartilage was represented with hexahedral elements as a nearly incompressible, neo-Hookean hyperelastic material and cortical bone was represented with triangular shell elements as an elastic homogeneous, isotropic material. Literature-based kinematics and kinetics were used to simulate descending stairs (DS), walking (W) and stair-climbing (SC). Average peak stresses and contact areas were calculated. Regional stresses were analyzed by mapping individual pelvic cartilage stresses to an average geometry, which was then divided into 4 anatomic regions (Anterior-A; Medial-M; Lateral-L; Posterior-P). A Kruskal-Wallis tested for significant differences in mean stress and variation in stress between anatomical regions within each loading condition. Stress distribution varied substantially among subjects during each loading scenario. Still, stresses as an average of all subjects corresponded to the anatomical alignment and direction of the equivalent joint reaction force, with peaks 13.1±3.95 (DS), 9.1±2.51 (W) and 12.0±4.78 (SC) MPa. Contact areas were 582±190 (DS), 732±175 (W) and 735±196 (SC) mm2. Regional differences of the averaged stresses were: A,M,L > P during DS; M,L > P during W; and M,L > P, M > A during SC. Inter-subject variance by region was: A,L > P during DS; M,L > P during W; and M,L > P,A during SC. Variations in contact stress demonstrate the differences between normal subjects despite identical loading, which is likely due to individual joint anatomy. The contact patterns and peak stresses in the current study were less uniform and higher than ideal geometry studies and in good agreement with in vitro data. Future work will apply the modeling technique to additional volunteers and may isolate the major factors that contribute to the stress variations in both healthy and pathological hip joints.