Collagen Fibre Orientation in Bone

Summary

Various models have been proposed in the past for the orientation of collagen fibres in bone. These features have been deduced from observations of demineralised bone specimens or implied by examination of thinly ground samples in polarised light. Such techniques cause significant disruption of the bone structure and so we have developed a method which retains the inherent rigidity of the mineral component of the bone. This technique is based on the removal of the collagen from a polished bone surface by use of a collagenase solution. The holes from which collagen has been removed are clearly revealed in the scanning electron microscope and the pattern of fibre orientation can easily be visualised. This technique has been applied to bones from a number of sources. The lamellar structure of bovine secondary osteons is shown to result from alternating layers of longitudinal and circumferential collagen fibres, slightly tilted from perfect alignment. Each branch of the bifurcated medullary cavity of frog tibial diaphysis is surrounded by a similar arrangement of lamellae also arising from layers of alternating collagen fibre orientations. The same features have been seen in bone samples from various other sources suggesting the widespread utilisation by Nature of alternating collagen fibre orientations in response to the environment, particularly stress patterns in the bone.