Collagen orientations in the meniscus of the knee joint.

X-ray diffraction shows that the collagen fibrils of dog, pig and human meniscus tend to be oriented circumferentially in the bulk tissue and radially in the surface region. Individual fibrils are not all oriented in these directions but are distributed about the preferred orientations with a standard deviation of around 15 degrees in the bulk tissue. Polarised light microscopy yields results which are consistent with X-ray diffraction. This technique also shows that the fibrils are aggregated into crimped fibres, resembling those of tendon, and that some of these fibres pass from the outer region of the meniscus into the bulk tissue. Artificial split lines demonstrate the radial orientation of outer fibres over most of the superior and inferior surfaces of the meniscus. Split lines reorient as they pass into the bulk tissue which is consistent with the interpretation of X-ray diffraction and polarised light microscopy results of this study. The pattern of collagen orientations is also consistent with the meniscus transmitting compressive load in the knee joint.