To investigate the topographical variations among the morphological and physical properties of articular cartilage over a canine humeral head.
Nine side-by-side specimens from a canine humeral head were used in the combined polarized light microscopy (PLM) and microscopic magnetic resonance imaging (muMRI). Sixteen images were acquired from each specimen in muMRI. Subsequently, ten to fourteen histological slices were prepared at the location of the muMRI slice from each specimen. Four optical images were acquired from each histological slice. Using these images, the images of the T(2) relaxation, the optical retardation, and the collagen-fiber orientation were constructed in two dimensions.
Along the medial/lateral direction of the humeral head, we have observed a number of topographical variations. These include the total thickness of the cartilage tissue, the thickness of the individual histological zones, the depth of the minimum optical retardation in the tissue, and the depth of the maximum T(2) relaxation in the tissue. We found that the depth of the minimum retardation from PLM occurs at the geometric middle point of the transitional zone in histology, and that the depth of the maximum T(2) relaxation from muMRI is closely correlated with the minimum retardation depth in PLM. In addition, although the thickness of the total tissue increases approximately by the same amount on both the lateral and medial sides of the joint, a slight asymmetry exists between the measurements from the medial and lateral halves of the humerus.
Cartilage from different sites over a single joint could have different properties, possibly the consequence of the variation in load-bearing status. Because of these topographical variations, one must keep in mind that a different sampling site within a relatively small area of the same joint may significantly influence the results of the study.