The Journal of Bone and Joint Surgery, Vol 62, Issue 7 1102-1117, Copyright © 1980 by Journal of Bone and Joint Surgery, Inc
The intrinsic tensile behavior of the matrix of bovine articular cartilage and its variation with age
V Roth and VC Mow
To study the age dependence of the uniaxial tensile behavior of bovine
articular cartilage, 216 specimens of articular cartilage from the
patellofemoral joint were grouped into two age categories: those from
joints with growth plates present (open physes) and those from joints
without growth plates (no physes). We prepared standard, dumbbell-shaped
test specimens from the three ultrastructural zones of the tissue: the
superficial tangential zone, the middle zone, and the deep zone. As was
done in the early works of Kempson et al. and of Woo et all., we prepared
specimens whose long axes were either parallel or perpendicular to the axis
of the local split line on the joint surface. In these tensile tests we
observed a profound difference between the two age groups in terms of the
variations in the tensile properties related to the depth below the
surface. With increasing distance from the articular surface, the tensile
strength and stiffness increased in the open-physis group and decreased in
the no-physis group. Directional dependence of the tensile response was
manifested by increased stiffness and strength of the samples oriented
parallel to the split-line axis when compared with the samples oriented
perpendicular to it. Distortion of the initially flat, straight-sided
portion of the gauge section was observed in most of the 216 specimens
immediately after the application of tensile strains. This effect casts
serious doubts on all previous measurements of cross-sectional dimensional
changes. At present, we believe that this distortion occurs because
articular cartilage is an inhomogeneous, layered material. We also observed
that cartilage exudes substantial amounts of its interstitial fluid when
the applied tensile strain becomes large. These two effects create serious
problems in assessing the true volumetric changes and the material
properties of cartilage specimens during uniaxial tension experiments.