Annals of West University of Timişoara, ser. Biology, 2014, vol XVII (2), pp.129-136
ASPECTS OF BONE TISSUE IN OSTEOPOROSIS
Rodica TÖRÖK-OANCE*1, Liliana VASILE2
1
Department of Biology-Chemistry, West University of Timisoara,
16 Pestalozzi, 300115, Timisoara, Romania
2
Department of Microscopic Morphology, Victor Babeș University of Medicine and Pharmacy
Timișoara, Piața E. Murgu 2, 300041, Timisoara, Romania
*
Corresponding author’s e-mail address: [email protected]
Received 20 November 2014; accepted 12 December 2014
ABSTRACT
Osteoporosis is the most common bone disease and its prevalence is increasing as the
population grows older. The aim of this study is to highlight changes of the bone tissue
which occur in osteoporosis and which affect bone quality. We identified several
aspects of the bone tissue in osteoporosis such as abundant cement lines, endosteal
bone resorption, the presence of thinned bone trabeculae, the presence of trabecular
microfractures, the disruption of intertrabecular connectivity and marked cortical
porosity. These changes influence bone quality and may contribute to increased bone
fragility in osteoporosis. We also revealed periosteal apposition, which in contrast
with the aspects mentioned above, has a beneficial effect on bone strength due to the
addition of bone material. Osteoporosis is the most common bone disease and its
prevalence is increasing as the population grows older. The aim of this study is to
highlight changes of the bone tissue which occur in osteoporosis and which affect
bone quality. We identified several aspects of the bone tissue in osteoporosis such as
abundant cement lines, endosteal bone resorption, the presence of thinned bone
trabeculae, the presence of trabecular microfractures, the disruption of
intertrabecular connectivity and marked cortical porosity. These changes influence
bone quality and may contribute to increased bone fragility in osteoporosis. We also
revealed periosteal apposition, which in contrast with the aspects mentioned above,
has a beneficial effect on bone strength due to the addition of bone material.
KEY WORDS: osteoporosis, bone tissue, bone quality
INTRODUCTION
Bone remodelling is a process that takes place continually throughout life. It
starts with the bone resorption, followed by formation and deposition of new bone in
the same place in which the resorption took place (Lerner, 2006). When more bone is
destroyed than is formed, bone loss occurs and it can cause osteoporosis (Adami,
2006), in osteoporosis the regenerative capacity of the bone being compromised
(Durao et al, 2012). Osteoporosis is the most common bone disease, affecting millions
of people worldwide, and its prevalence is increasing as the population grows older
(Werner, 2000). Osteoporosis remains often undiagnosed and untreated, partly because
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TÖRÖK-OANCE & VASILE: Aspects of bone tissue in osteoporosis
it is not always clinically evident until a fracture occurs (De Gabriele, 2006).
Nontraumatic fractures in osteoporosis are common, they occur in weakened bones
under normal mechanical stress (Damilakis et al, 2007). Bone fragility can be defined
briefly as the susceptibility to fracture (Turner, 2002). Fracture risk is not always
accurately assessed by osteodensitometry, a high fracture risk could be caused by an
abnormal bone quality (Compston, 2006). This paper aims to highlight some changes
of the bone tissue which occur in osteoporosis and which affect the bone quality.
MATERIALS AND METHOD
The study material consists of bone fragments of ribs and iliac crests collected
at the Institute of Forensic Medicine from Timisoara. In order to obtain the histological
material on which the study was conducted, we used the histological technique of
permanent preparation (Raica et al, 1996; Vasile et al, 2002). The fixation was made in
10% formallin. Decalcification was performed with a working solution consisting of
equal quantities of 8% standard hydrochloric acid solution and 8% standard formic
acid solution. The bone fragments were maintained in the decalcification solution until
softening, when they could undergo embedding, sectioning and staining operations.
The fragments were embedded in paraffin and the paraffin blocks were sectioned using
the microtome, then the Haematoxylin and Eosin staining and Masson trichrome
staining were performed. The analysis of histological samples was carried out under an
optical microscope Nikon E200 and pictures were taken using the digital microscope
camera.
RESULTS AND DISCUSSIONS
In the present study, we observed, both in the cancellous bone and compact
bone, the presence of numerous cement lines (Fig.1), which suggest an intense bone
remodelling. Cement lines indicate the deepest penetration place of bone resorption, on
top of which newly formed bone tissue is accumulating. Such a highly remodelled
bone is structurally weaker than the primary lamellar bone of younger adult. The
cement lines are places of minimum strength (Marcus, 1996).
We noticed on some samples aspects of endosteal bone resorption (Fig. 2).
Concerning the remodelling at the endosteal surface, Brown et al (1987) stated that
there is an increased bone turnover in this area, and underlined its significant
contribution to bone loss in osteoporosis.
Some of the other changes highlighted on the analysed material are the
presence of thinned bone trabeculae (Fig. 3), as well as of microfractures (Fig. 4).
The thinning of the bone trabeculae contributes to weakening the mechanical
strength of the osteoporotic bone. With respect to the bone microdamage, they are also
likely to occur in healthy bone, but can be repaired by remodelling, which prevents
their accumulation (Clarke, 2008). Mori and Burr (1993) showed that bone
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Annals of West University of Timişoara, ser. Biology, 2014, vol XVII (2), pp.129-136
remodelling is prevalent in regions with microdamage caused due to fatigue and is
subject to a direct cause-effect relationship between the occurrence of the bone
microdamage and its repair. The bone has an operational microdamage threshold. If
bone stress and deformations are below this threshold, remodelling units can repair the
microdamage, but the stress above this threshold creates a number of microdamages
exceeding the restoring capacity of bone tissue, which will accumulate over time and
cause the occurrence of nontraumatic fractures (Frost, 2003).
Trabecular fractures lead to disruption of trabecular connectivity (Fig. 4B).
The decrease of trabecular connectivity has consequences on the strength of the
trabecular system. It has been shown that an equivalent amount of bone mass
distributed in thick trabeculae, distant from each other and with reduced connection is,
from a biomechanical perspective, less competent than if it were structured in several
thinner and more intensely interconnected trabeculae (Davison et al, 2006).
FIG. 1. Marked bone loss by osteolysis. Multiple cement lines present within bone tissue suggesting a reactive
bone response to the load of forces acting upon the bone (Masson trichrome staining, x400).
FIG. 2. Endosteal bone resorption in cancellous bone with adaptive remodelling, trabecular microfracture (HE
staining, x200)
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TÖRÖK-OANCE & VASILE: Aspects of bone tissue in osteoporosis
FIG. 3. Thinned bone trabecula under osteoporotic conditions (Masson trichrome staining, x200).
FIG. 4. A: Osteolysis and trabecular microfracture in involutional osteoporosis (HE staining, x200); B: Bone
area adjacent to a fracture point with ischemic necrosis of the bone and myeloid tissue, disruption of trabecular
connectivity (HE staining, x200).
We have also noticed on certain sections aspects that suggest the destruction of
some connecting trabeculae, associated with an irregularity of the remaining bone
trabeculae (Fig. 5). We try to explain the presence of this trabeculae dimensional
variety by a compensating mechanism, initiated as the attempt of the bone to
supplement the decrease in strength due to the resorption of the connecting trabeculae.
As the connecting trabecular elements disappear, the mechanical load shall rest upon
the remaining trabeculae, which can become thicker as a compensating measure.
We have also highlighted some changes at bone marrow level of the
cancellous bone. In this case, we have found aspects of its adipose degeneration (Fig.
6A). Our findings are similar to those of Verma et al (2002), who showed that the
decrease of cancellous bone is associated with the decrease of bone marrow cellularity,
while the adiposity at medullar level increases. In some cases we also noticed the
presence of enlarged areolar spaces with reduced myeloid content (Fig. 6B). In other
cases we observed necrobiosis of the myeloid tissue (Fig. 6C). This modifications
could be explained based on the changes in the blood infusion at bone level.
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FIG. 5. Thickness variability and irregularity of bone trabeculae (Masson trichrome staining, x200).
Fig. 6. A: Bone areolae with adipose degeneration of hematogene marrow (Masson trichrome staining, x200); B:
Pneumatization of osteoporotic cancellous bone by widening the areolar spaces, some without content or with
necrobiotic myeloid tissue, microfractures of bone trabeculae (HE staining, x 200); C: Augmenting the bone
porosity by trabecular osteolysis. Partial necrobiosis of myeloid tissue (Masson trichrome staining, x200) .
Increased cortical porosity is another aspect noticed in some of the analysed
histological samples (Fig. 7). Porosity refers to the prevalence and the dimensions of
intracortical cavities. It has been shown that intracortical porosity undergoes a sudden
increase in women after menopause, becoming significantly different from young
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TÖRÖK-OANCE & VASILE: Aspects of bone tissue in osteoporosis
adults at around sixty years, while in men the increase is slower, and the difference
becomes significant at about eighty years (Davison et al, 2006). Increasing porosity
that occurs with age is reflected in the changes of the properties of bone material,
which also occur with age, and thus the high incidence of fractures (Stein et al, 1999).
FIG. 7. Osteoporotic reactive cortical bone presenting osteons with very large Haversian canals in relation to
their size, through the lamellar structure of the osteon (Trichrome staining, x400).
FIG. 8. Bone areola with spheruloid aspect at the periphery of the cancellous bone, close to the cortical bone
repaired by periosteal apposition (Trichrome staining, x200).
Another aspect that we have observed on some sections is that of periosteal
apposition (Fig. 8). There are at least two reasons which can explain the existence of
periosteal apposition. Since the estrogen has an inhibiting effect over bone formation at
periosteum level, the decrease of estrogen after menopause will be followed by
periosteal bone apposition. Another explanation is the fact that bone loss at endosteal
level leads to increased stress within the bone tissue, which will enhance the number
and / or activity of bone forming cells on the periosteal surface of the cortex, driving
bone formation (Ahlborg et al, 2003). This modelling phenomenon does not occur in
bone regions which lack periosteum (Bonjour et al, 1994). Periosteal apposition is
regarded as an adaptive response for the purpose of conserving bone strength
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throughout ageing and endocortical bone resorption (Jepsen & Andarawis-Puri, 2012).
On the other hand, there are studies that show that periosteal apposition is reduced
after menopause onset (Szulc et al, 2006).
CONCLUSIONS
On the analysed histological material we identified several aspects of the bone
tissue under osteoporotic conditions, which are abundant cement lines, endosteal bone
resorption, the presence of thinned bone trabeculae, the presence of trabecular
microfractures, the disruption of intertrabecular connectivity and marked cortical
porosity. These changes influence bone quality and may contribute to increased bone
fragility in osteoporosis. As more of these changes are present simultaneously, by
cumulative effect, so it increases the impact on bone strength and the bone fragility.
Conversely with the other aspects mentioned above, the periosteal apposition, also
highlighted herein, due to the addition of bone material, has a beneficial effect on bone
strength.
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