An approach to the histomorphological and histochemical variations of the humerus cortical bone through human ontogeny

Abstract

For many years, clinical and non-clinical investigations have investigated cortical bone structure in an attempt to address questions related to normal bone development, mineralisation, pathologies and even evolutionary trends in our lineage (adaptations). Research in the fields of medicine, materials science, physical anthropology, palaeontology, and even archaeobiology has contributed interesting data. However, many questions remain regarding the histomorphological and histochemical variations in human cortical bone during different stages of life. In the present work, we describe a study of long bone cortex transformations during ontogeny. We analysed cross-sections of 15 human humeri histomorphologically and histochemically from perinatal to adult age, marking and quantifying the spatial distribution of bone tissue types using GIS software and analysing the mineral composition and crystallinity of the mineralised cortex using Raman spectroscopy and X-ray diffraction. Our results allowed us to propose that human cortical bone undergoes three main 'events' through ontogeny that critically change the proportions and structure of the cortex. In early development, bone is not well mineralised and proportionally presents a wide cortex that narrows through the end of childhood. Before reaching complete maturity, the bone mineral area increases, allowing the bone to nearly reach the adult size. The medullary cavity is reduced, and the mineral areas have a highly ordered crystalline structure. The last event occurs in adulthood, when the 'oldest' individuals present a reduced mineralised area, with increasing non-mineralised cavities (including the medullary cavity) and reduced crystalline organisation.

Keywords: Raman spectroscopy; compartmentalisation; cortical bone; histology; humerus.

Figure 1

Complete left humeri (top row) and cross-sections after image processing (bottom row). The black bar in the left column represents the scale bar, 10 cm in the upper row and 10 mm in the bottom row.

Figure 2

Perinatal bone cross-sections. The top row shows compartmentalisation, the middle row shows different bone tissues, and the bottom row shows Raman spectroscopy data. The line plot represents the mean Raman spectrum values after background fluorescence subtraction, and the grey colour represents the standard deviation among the 12 points sampled in each individual. The black bar plots in the upper right corner (bottom row) show raw Raman intensity values after signal processing (fluorescence subtracted). Scale bars: 5 mm (vertical white bar, upper left corner in top and middle row). See Table 1 for abbreviations.

Figure 3

Infant bone cross-section analysis. See Fig. 2 for details. Scale bar: 5 mm (vertical white bar in the upper left corner in the top and middle rows).

Figure 4

Juvenile bone cross-section analysis. Details as in previous figures. Scale bar: 5 mm (vertical white bar in the upper left corner in the top and middle rows).

Figure 5

Adult bone cross-section analysis. Details as in previous figure. Scale bar: 5 mm (vertical white bar in the upper left corner in the top and middle rows).

Figure 6

Compartmentalisation (upper) and bone tissue typology (bottom) variation during growth. Adult individuals appear ordered, supporting our proposal (see Discussion for details). In the upper plot, the black line represents the ratio between the mineralised (MA) and non-mineralised areas (MC + vascularisation). The bottom plot represents the percentages of different bone tissues, establishing the difference between modelling (bottom left) and remodelling (upper right).

Figure 7

X-Ray diffraction (XRD) characterisation of the different ontogenetic groups. Note the gradual crystalline increase from perinatal to juvenile and adult individuals. Vertical lines represent hydroxyapatite (HDA) peak characterisation.