Measurement of biaxial optical birefringence in articular cartilage.

Optical birefringence is a valuable parameter in evaluating collagen organization and assessing collagen degeneration in articular cartilage. A uniaxial birefringent model is implied when using existing methods such as polarized light microscopy in characterizing birefringence in cartilage. However, some studies suggest the existence of a sheet-like collagen organization in articular cartilage, which requires a biaxial birefringence model to describe. In this study, we applied a multi-incident birefringence measurement procedure to investigate the biaxial birefringence in articular cartilage. The results supported the existence of a small yet significant biaxial birefringence effect, which was in agreement with the expectation from a sheet-like collagen organization.