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Structural periodicity in human articular cartilage: comparison between magnetic resonance imaging and histological findings.

OBJECTIVE
To relate the vertical striations visualized in the deeper layers of articular cartilage by Magnetic Resonance Imaging (MRI) to histological features.


METHODS
Two knee joints recovered at post-mortem from males in their seventies with no history or visual evidence of joint disease were examined. MR images were obtained in a 4.7 T 400 mm-bore magnet, after which the knees were fixed, sectioned, and examined histologically.


RESULTS
High resolution MR showed vertical high/low signal striations with a two to three-fold variation in signal intensity and a periodicity of 0.56 (+/-0.16 mm), most prominent in weight bearing areas. Histological sections revealed alternating light and dark staining areas with a periodicity of 1.01+/-0.54 mm in the lower zones of the cartilage, some, but not all of which clearly represented folding. Given that MR will only visualize vertical structures in cartilage aligned at 90 degrees, whereas histology will cut them at varying angles, it is likely that the vertical structures seen by each modality correspond, and that they represent structural heterogeneity in cartilage; perhaps the presence of plates of high collagen and proteoglycan content.


CONCLUSION
The vertical striations seen routinely in the deep zones of hyaline articular cartilage on histological sections are not artefactual; they are likely to represent structural heterogeneity due to the presence of areas of high collagen and high proteoglycan content that exist in weight-bearing areas. This structural heterogeneity may be of great importance to the integrity and function of the cartilage.