Physical indicators of cartilage health: the relevance of compliance, thickness, swelling and fibrillar texture.

This study uses a bovine patella model to compare the relative merits of on-bone compliance and thickness measurements, free-swelling behaviour, and structural imaging with differential interference contrast (DIC) light microscopy to assess the biomechanical normality of the cartilage matrix. The results demonstrate that across a spectrum of cartilage tissues from immature, mature, through to mildly degenerate, and all with intact articular surfaces, there is a consistent pattern of increased free swelling of the isolated general matrix with age and degeneration. High swelling was always associated with major structural alterations of the general matrix that were readily imaged using DIC light microscopy. Conversely, for all tissue groups, no relationship was observed between thickness vs. compliance and compliance vs. general matrix swelling. Only in the proximal aspects of the normal mature and degenerate tissues was there a correlation between thickness and general matrix swelling. Free-swelling measurements combined with fibrillar texture imaging using DIC light microscopy are therefore recommended as providing a reliable and quick method of assessing the biomechanical condition of the cartilage general matrix.