The spatial arrangement of bone mineral as revealed by ion bombardment

Mineral changes in osteoporosis: a review

Bone mineral composition, crystallinity, and bone mineral content of osteoporotic patients are different from those of normal subjects. We review the evidence that these mineralization parameters contribute to the strength (fracture resistance) of bone and the methods that have been used to examine them. A specific example is provided from analysis of biopsies from the Multiple Outcomes in Raloxifene Evaluation trial. For the analyses, randomly selected biopsies from placebo, low-dose, and high-dose groups (n = 5 per group) obtained at time zero and 2 years after treatment were examined by infrared imaging spectroscopy. In all cases, comparable increases in mineral content were found, but there were no significant variations in mineral crystallinity.

Osteoporotic bone microstructure by collagenase etching

Collagenase etching has been used to show the microstructure of bone from patients suffering from primary osteoporosis. Both polished and unpolished surfaces of trabecular bone from femoral heads were treated with collagenase solution before study in the scanning electron microscope. The polished surfaces show the mineral component of this bone as small rounded units approximately 10-20 nm across, which aggregate to form a continuous phase of contiguous spheroidal particles approximately 100 nm across. Lamellations are clearly seen to be due to the removal of collagen fibres up to approximately 200 nm across, fibres in adjacent lamellae being arranged approximately perpendicular to each other. The unpolished surfaces also show small rounded units, which aggregate into rods of mineral approximately 100 nm across. Although these rods form a connected system, they are loosely packed, compatible with their being interspersed with the collagen fibres in vivo. This model for the detailed microstructure of bone is consistent with specimens from a number of other sources and shows no features unique to osteoporosis.

Mineral structure and preferred orientation in the fin bones of the plaice, Pleuronectes platessa

The technique of collagenase etching of a polished surface of plaice fin bone has been used to reveal the structural detail of the mineral component and hence to explain the preferred orientation previously deduced from X-ray diffraction experiments. High resolution electron micrographs reveal units approximately 20 nm across, which aggregate to form units approximately 100 nm across, which in turn coalesce to produce rods up to approximately 1 micron diameter and of substantial length. These rods show a preferred orientation with their axes parallel to the long axis of the bone, thus demonstrating a preferred orientation of the mineral component. Additionally, collagenase-etched transverse surfaces reveal numbers holes from which collagen fibrils parallel to the long axis of the bone have been removed, whereas similarly treated longitudinal surfaces do not show such holes. This is consistent with a predominance of collagen fibrils running along the bone axis and explains the previously observed preferred orientation of the collagen component of fish fin bones.

Bone microstructure by collagenase etching

A novel technique has been developed for microstructural studies of bone. The spatial organizations of the mineral and collagen fibres in bone have been a matter of discussion for some time, with numerous diverse observations arising from various preparative techniques. In this latest investigation details of the mineral structure are clearly revealed in the SEM by treating a cut and polished surface of bone with collagenase to remove the major organic component. This new procedure has minimal effect on the mineral and hence reveals microstructural detail which is far closer to that in vivo than in previous investigations. This paper concentrates on two aspects of the studies, namely the detailed morphology of the mineral component and the arrangement of the collagen fibres in the osteons of compact bone. Firstly, the mineral component is revealed as comprising 'crystallites' (approximately 20 nm diam.) which aggregate to form larger contiguous 'spheroidal particles' (approximately 100 nm diam.), which in turn form 'granules' (approximately 500 nm diam.). Secondly, the regions from which collagen fibres have been removed are clearly revealed, showing that within an osteon, alternating lamellae have collagen fibres oriented approximately parallel to and circumferential to the Haversian canal respectively.