Age-related changes in bone architecture Alterações na estrutura óssea relacionadas à idade

Objective: to evaluate the histologic and morphometric characteristics of bone biopsies of the anterior iliac crest of patients of different age groups. Methods: we studied 30 bone samples from the iliac crest, using brightfield optical microscopy. We divided the samples by donors’ age groups in three groups: Group 1 (n = 10), subjects aged between 25 and 39 years; Group 2 (n = 10), subjects aged between 40 and 64 years; Group 3 (n = 10), individuals aged 65 years and over. We randomly divided the samples into two sets with 15 specimens. In the first study segment (n = 15), we used histological to assess the osteogenic property of the graft, through the analysis of cell reserve in the periosteum, the number of osteocytes in the lacunae and the number of Haversian and Volkmann’s canals. In the second study segment (n = 15), we investigated the morphology of osteoconductive property of the graft, through quantification of the trabecular meshwork (Vv) and trabecular area (Sv). Results: histologically, we observed degeneration of bone occurring with age, characterized by thinning of the periosteum, with gradual replacement of the steogenic layer by fibrous tissue, small amount of Haversian and Volkmann’s canals, osteocyte lacunae voids and fine spongy bone trabeculae, allowing ample medullary space, usually occupied by fat cells and adipocytes. Morphologically, with respect to the quantification of the trabecular meshwork (Vv), we found statistically significant differences between Groups 1 and 3 and between Groups 2 and 3, with reduction of the trabecular meshwork of about 45% in the elderly over 65 years old ; there was no statistically significant difference between Groups 1 and 2. There was also no statistical difference between the Groups regarding Sv. Conclusion: the results of this experiment suggest that, in the elderly (over 65 years old), the osteogenic property of autologous bone graft decreases and the osteoconductive property is compromised.

substitute could display all these features 5,6 . Nevertheless, several authors have pointed out disadvantages and com-plications related to the use of autografts 7,8 . The sources and the amount of grafts are limited and the morbidity in the donor site is frequent, ultimately exerting profound effect on treatment outcome. Furthermore, recent studies have shown reduced osteogenic potential in some clinical situations, such as diabetes mellitus, advanced age and after chronic use of corticosteroids, nicotine and alcohol [9][10][11] .
The purpose of this study was to evaluate the histologic and morphometric characteristics of bone biopsies from the anterior iliac crest of patients of different age groups, using brightfield optical microscopy.

METHODS
In a period of six months, we collected 57 bone fragments of the anterior iliac crest of patients undergo-Giordano Age-related changes in bone architecture ing orthopedic surgery in the orthopedics service of the lead author. All patients signed an informed consent and the Review Committee of the lead author Institution approved the study.
Of the 57 biopsies performed, we selected the 30 best specimens for microscopic analysis; of these, we randomly selected 15 for histological analysis and 15 for morphometric analysis. We divided the material by donors' age group in three groups: Group 1 (n=10), subjects aged less than 39 years; Group 2 (n=10), subjects aged between 40 and 64 years; Group 3 (n=10), individuals aged 65 years and over. Tables 1 and 2 show the patients' demographic data.
We operated all patients on in the supine position. To remove the graft,we performeda curvilinear access on the anterior iliac crest of approximately 5cm by dissection of planes till reaching the periosteum. We withdrew a 1cm³ corticocancellous block, preserving the periosteum. We used electrocautery during the bone biopsy. We placed the material in vials containing 3ml of buffered 10% paraformaldehyde for five days and then sent them for histological and morphometric studies.
Histological Analysis: After fixation, the fragments were decalcified in 5% nitric acid for five days, dehydrated in alcohol, cleared and embedded in paraffin.
We used a Spencer® microtome (American Optical, USA) to make 5μmthick sections, sagittal to the longitudinal plane of the bone block. The sections were stained with hematoxylin-eosin (H&E), according to the methodology described by Bancroft and Cook 12 . We used a brightfield optical microscope (Olympus BHs-RFCA, Japan).
The same researcher performed the histological readings, blindly, systematically, and according to a pre-defined script (Table 3).
Morphometric analysis: After fixation, the fragments were decalcified in 5% nitric acid for five

Cancellous bone
In the young (Group 1), the bone marrow found was intact, generally presenting small areas of necrosis in the periphery and, less often, bleeding areas. The bone trabeculae were clearly visible, quite thick, making networks with continuity aspect ( Figure   3A). There were no osteoclasts. In subjects in Group 2 (between 40 and 64 years), the bone marrow was full, with peripheral areas of necrosis and hemorrhage. The

DISCUSSION
The development of new biomaterials to mimic the characteristics of autologous bone graft has advanced in recent years. In vitro and clinical investigations have suggested that some of these bone substitutes may actually stimulate consolidation 18,19 . However, the great diversity among the biomaterials available and poor understanding of the mechanisms by which these substances participate in the bone repair process limit their application 2,18 . Even today, the use of the autograft is the best solution for reconstruction of large bone defects and osteogenic stimulating bone healing 2-5 . Its unique structure provides an excellent mechanism of self-regulation and functional adaptability. Its

Figure 3. Photomicrograph of histological sections of the anterior iliac crest biopsies of adults -CANCELLOUS BONE. A (Group 1) -thick bone trabeculae forming networks with small medullary space (H&E, 100X); B (Group 2) thinner bone trabeculae, but still forming networks with increased medullary space compared with Group 1 (H&E, 100X); C (Group 3) -thin and broken bone trabeculae, with large medullary space filled with fat cells and adipocytes (H&E, 100X).
solid matrix facilitates the exchange of biomechanical, biochemical and electromechanical signals, endogenous and exogenous of system to which it is exposed to,to the cells responsible for bone modeling 6,20 . Based on these authors' findings [21][22][23][24] , in this experiment we studied histologic and morphometric characteristics of bone biopsies from the anterior iliac crest.
We divided patients into three groups of different age groups. With regard to Groups 1 and 2, we set the division based on the hormonal decline and consequent deterioration of bone tissue microstructure that occur around 40 years of age, especially in women. There is a direct relationship between low bone density and pathologic fractures 25 . The inclusion of Group 3 followed the guidelines of the World Health Organization, which considers "elderly" individuals aged 65 years and over 26 .