How the structural integrity of the matrix can influence the microstructural response of articular cartilage to compression.

This study investigated how the structural integrity of healthy, surface-removed (healthy), and degenerate matrices can modify the response of cartilage to compression. Six groups of specimens were loaded up to the onset of consolidation or at full consolidation (N = 30, 5 per group, respectively) and then subsequently chemically fixed to capture the deformed state of the tissues. Creep compression was applied through an 8 mm flat-ended indenter containing a 450 μm diameter central pore, providing a region of high stress that also allowed the tissue samples to deform freely around the indenter pore during compression. Differential interference contrast microscopy was used in order to explore the microstructural responses of the tissues. The results demonstrated that superficial layer removal or tissue degeneration can reduce the observed deformation within the tissue region corresponding to the central pore of the loading indenter. Fibril crimping within the central pore matrix and matrix shear at the indenter edge regions are also reduced by both superficial layer removal and by tissue degeneration. These findings suggest that surface removal or tissue degeneration renders the matrix more susceptible to deformation and can also reduce the tissue's ability to transfer forces over a greater surface area and induce stress within the matrix.