Structural changes in the ageing periosteum using collagen III immuno-staining and chromium labelling as indicators.

The periosteum and Sharpey's fibre extensions occupy the musculoskeletal interface and may be strategic in age-related deterioration. Because of its exceptionally powerful insertions the porcine mandible is an ideal model and its periosteal system was compared in 4 separate regions of adult young (1 year) and older (3 year) animals. These were examined by undecalcified histology, collagen immunohistochemistry and mineral histochemistry using polarization, epifluorescence and laser confocal microscopy; mineral ultrastructure was facilitated by chromium labelling with EDX microanalysis. Birefringent Sharpey's fibres were coarse (>8 microm) or fine and classified as horizontal (more common with age), oblique (most common in youth) or vertical (least common); in addition they were designated "superficial", "transcortical" and "intertrabecular" (the latter being deep, coarse and vertical). Their specific affinity for collagen type III FITC-labelled antibody demonstrated 3-dimensional arrays of bone-permeating fibres. With age at each region the cortical thickness rose (e.g. 4.9 mm to 9.3 mm), the periosteum thinned (e.g. 180-/+7 microm to 129-/+8 microm; p<0.001), and the periosteum: bone ratio diminished (e.g. 3.65-/+0.36 to 1.40-/+0.14; p<0.001) while Sharpey's fibres became fewer, fragmented, superficial and shortened (e.g. 226-/+27 microm to 55-/+6 microm; p<0.001). Accompanying was the sporadic encroachment of calcified particles, 1 microm diameter, in irregular periosteal aggregates or interlinked around Sharpey bundles (resembling calcifying turkey leg tendon). EDX microanalysis confirmed prominent chromium spectral peaks in the older periosteum only, coincident with chromium-labelled mineral "ghosts". It was concluded that the periosteum and Sharpey's fibres, deep-penetrating and complex in youth, partially hardens and regresses with age with implications for its functional properties.