|Year : 2017 | Volume
| Issue : 1 | Page : 25-30
Correlation between bone histomorphometry and bone strength
MK Jindal1, OP Lakhwani2, SK Kapoor2, RK Chandoke3, Omkar Kaur3, BB Arora4, Keerty Garg5
1 Department of Orthopaedics, Kalpana Chawla Government Medical College, Karnal, Haryana, India
2 Department of Orthopaedics, ESI-PGIMSR, Basaidarapur, India
3 Department of Pathology, ESI-PGIMSR, Basaidarapur, India
4 Department of Mechanical Engineering, Delhi Technological University, New Delhi, India
5 Department of Anaesthesia, Guru Nanak Medical College, Amritsar, India
|Date of Web Publication||11-Jan-2017|
M K Jindal
Department of Orthopaedics, Kalpana Chawla Government Medical College, Karnal, Haryana
Context: The structural and mechanical characteristics of bone have been extensively studied to understand the functional adaptations associated with the properties of biological material. While measures of apparent density used as an estimate of mechanical properties do not account for the structural organization of the trabecular bone, thus rendering this scalar measure inadequate for predicting the material properties. Structurally bone can be divided into macro- and micro-structure. Whereas macrostructure can be understood in terms of its mass, shape, and density of the bone, microstructure is related to bony trabecular meshwork. Thus, the evaluation of bone microstructure plays an important role in defining material properties of bone including the bone strength. Aim: This study uses histomorphometric parameters and compares the same with compression strength of cancellous bone. Materials and Methods: Static histomorphometric parameters such as trabecular number, trabecular thickness, trabecular separation, and bone volume were calculated using 40 cubical specimens obtained from femoral heads of patients who underwent hip replacement procedures. These cubes were subjected to uniaxial compression test and yield point at failure calculated and results compared with histomorphometric indices. Discussion and Conclusions: We found the best correlation between bone volume microstructural parameter and uniaxial compression strength. The order of significance was bone volume (Spearman correlation 0.9652) > trabecular number (Spearman correlation 0.7646) > trabecular separation (Spearman correlation 0.7541) > trabecular thickness (Spearman correlation 0.6726). We concluded that microstructural parameters are valid predictors of bone strength and hence, noninvasive in vivo imaging modalities need to be developed which use these parameters to assess the risk of fracture.
Keywords: Bone mineral density, fracture, histomorphometry, osteoporosis
|How to cite this article:|
Jindal M K, Lakhwani O P, Kapoor S K, Chandoke R K, Kaur O, Arora B B, Garg K. Correlation between bone histomorphometry and bone strength. Trop J Med Res 2017;20:25-30
|How to cite this URL:|
Jindal M K, Lakhwani O P, Kapoor S K, Chandoke R K, Kaur O, Arora B B, Garg K. Correlation between bone histomorphometry and bone strength. Trop J Med Res [serial online] 2017 [cited 2017 Jun 28];20:25-30. Available from: http://www.tjmrjournal.org/text.asp?2017/20/1/25/198107
| Introduction|| |
The structural and mechanical characteristics of bone have been extensively studied to understand the functional adaptations associated with the properties of biological material. It is known that morphology varies between bones and even within a bone (Whitehouse 1974),,, as do the mechanical properties., While measures of apparent density used as an estimate of mechanical properties do not explain all the variance nor does it account for the structural organization of the trabecular bone, thus rendering this scalar measure inadequate for predicting the material properties.
Structurally bone can be divided into macro- and micro-structure. Whereas, macrostructure can be understood in terms of its mass, shape, and density of the bone, microstructure is related to bony trabecular meshwork. Materials engineering has demonstrated that all the material properties including mechanical properties are a function of material microstructure understood as spatial properties and arrangement of constituent basic structural elements, in the case of bone these being the trabeculae. Thus, the evaluation of bone microstructure plays important role in defining material properties of bone including the bone strength.
At present, bone mineral density (BMD) is considered the standard method to evaluate bone strength and stratify risk of fracture., However, while easy to administer, the limitation of relying on BMD measurements is that they are uniplanar measurements in terms that the three-dimensional (3D) structure of bone is reduced to two dimensions and then, the BMD values are computed. Furthermore, BMD measures only the mineral component of bone and does not give any information regarding its microstructure. Furthermore, studies have shown that higher BMD measurements do not directly translate to mechanical properties of bone and fracture risk.,
The relationship between trabecular microarchitectural pattern and bone strength has long been proposed. The importance of trabecular arrangement in bone and their significance in bone strength was first observed by Hermann Von Meyer an anatomist and Karl Culmann, an engineer. This arrangement of trabeculae ensures the maximum strength with the available bone material. Julius Wolff also based his theory on the similarity of trabecular pattern and maximum stress which formed the main idea in Wolff's law. The possibility that the distribution of trabeculae depends on the prevailing direction of the mechanical forces has been viewed by some authors as being in line with the mathematical calculations, but it has been evaluated cautiously by others, especially because of the complicated effects the traction of muscles may have on the overall load. In any case, there is a close relationship between the numbers and arrangement of trabeculae and the strength of spongy bone. This is confirmed by the fractures which can follow the age-induced loss of trabeculae, whose total volume can fall, at least in the iliac crest, from about 25% in youth to about 12% in the elderly. The loss is rather selective, as is shown by the falling frequency of transverse trabeculae and the persistence of vertical ones in the central zone of the osteoporotic vertebral bodies, and by the total disappearance of individual trabeculae in elderly women, and the generalized, sharp fall in their numbers in elderly men. This selective effect may be very dangerous because it causes not only a fall in bone volume but also a breakdown in bone's connectivity that is, the trabecular frame which greatly contributes to the strength of spongy bone.
Histomorphometric evaluation of these microstructural indices has the potential of giving a better estimate of actual bone strength than BMD values. Currently, micro-architecture of trabeculae can be measured by several histomorphological parameters such as the number of trabeculae defined in a given volume (Tb.N), their mean thickness (Tb.Th), their average separation distance (Tb.Sp), and their 3D volume (BV/TV).
This study uses these static indices of histomorphometry and BMD and correlates the same with the actual bone strength measured using performing uniaxial compression tests on the bone sample.
| Materials and Methods|| |
In this experimental in vitro study carried in 2012-2014, femoral heads were retrieved from patients (>60 years age group) undergoing surgical hip replacement procedures for fracture neck of femur were included the study. The femoral heads so obtained were made devoid of all soft tissue and cartilage and cut into cubical pieces. Exclusion criteria included femoral head involved in-infection, Paget's disease, rheumatoid arthritis, osteoarthritis, neoplastic conditions, pathological fractures, and other pathological conditions which were nonrepresentative of the general population.
Each piece was subjected to histomorphometric analysis and uniaxial compression tests.
Biomechanical compression testing
Each piece of the bone sample was tested for failure in compression tests using (model 4482, Instron Corporation) at a constant unilateral deformation rate 0.5 mm/s [Figure 1]. The resultant deformation curve was analyzed and yield point calculated.
|Figure 1: The compression test being carried on the cubical bone specimen using instron 4482 at a compression rate of 0.5 mm/min|
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Bone histomorphometry is a quantitative histological examination of bone to access microstructure and predict the biomechanical strength.
The cancellous bone graft material decalcified using 5% nitric acid for10 days (solution changed every 2 days) then dehydrated in ascending grades of alcohol, cleared in xylene and embedded in paraffin. Paraffin sections of 5 ΅m cut using microtome and stained with H and E. The image was processed using Nikon-based computerized softwares (×40 magnification) and histomorphometric parameters calculated.
Parameter undertaken to analyze the structure include:
- Bone volume (trabecular bone volume/tissue volume): Represents the area occupied by the trabeculae versus the total area of the field. Trabecular bone volume (volume of total cancellous bone) measured and expressed as percentage [Figure 2]
- Trabecular number: Number of trabeculae per unit area. In this study, single high power is taken as unit area [Figure 3]
|Figure 3: Microscopic image for calculation of trabecular number in the same sample trabecular number was calculated and found to be 74 in number (×40)|
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- Trabecular thickness: Mean trabecular thickness is measured and analyzed [Figure 4]
|Figure 4: Microscopic image for calculation of trabecular thickness in the same sample. Mean trabecular thickness was calculated and found to be 161.03 μm (×40)|
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- Trabecular separation: Mean of the average distance between the two trabeculae is measured and analysed [Figure 5].
|Figure 5: Microscopic image for calculation of trabecular seperation in the same sample. Mean Trabecular seperation was calculated and found to be 423 ƒÊm (×40)|
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| Results|| |
Material density versus bone strength
The analysis was performed to find an association between material density (real density = weight of the cube/volume of the cube) to the ultimate bone compression strength (in terms of its yield point in MPa). As seen from the Scatter Diagram 1 plotted (values near the central line) with the measured bone strength (uniaxial compression test) on y axis versus the square of the material density measured at the time of procurement on x axis and a statistically significant (Spearman rank coefficient 0.9737) correlation was found between the square of material density and bone strength of retrieved femoral head and hence, it may be used use as a measure of bone strength.
Microstructural parameters as a measure of bone strength
The analysis was performed between all measured values of microstructural parameters and compared to their corresponding compression strength measured through their corresponding yield point.
Scatter Diagrams 2-5 show the correlation between the microstructural parameters studied versus the uniaxial compression strength.
| Discussion|| |
Measures of bone strength
BMD measured by dual-energy X-ray absorptiometry (DXA), has been traditionally used for the diagnosis of osteoporosis and thereby bone strength.
However, recent research is indicating that the DXA test is not as reliable a measure of bone strength as originally thought. In fact, several studies have shown that many fractures occur in people with only moderately decreased BMD. Further, half of all postmenopausal fractures occur in women with BMD test results that indicate that their bone density levels are not low enough for them to be categorized as having osteoporosis.
Bone quality is measured by various microstructural indices, that is, trabecular number, trabecular separation, trabecular thickness, and bone volume which are measurable by histomorphometry (Parfitt 1987).,,,
The normal trabecular bone is composed of internal rods or plates that form a 3D branching lattice oriented along the lines of stress. The trabecular interstices of the axial skeleton are the primary repository of red bone marrow, therefore trabecular bone lies in proximity with the marrow-derived cells that participate in bone turnover. Bone loss initially starts at the bone surfaces; therefore, changes in osteoporosis first occur on the trabecular meshwork and weaken the same rather than affecting the bone density which is involved at a later stage.
Osteoporosis causes disruption of trabecular continuity by trabecular perforation, resulting in reduced connectivity of the trabecular bone structure, increased bone fragility and increased fracture risk; and the conversion of the normal plate-like trabeculae into thinner rod-like structures, resulting in changes in microstructural parameters like an increase in trabecular number decrease in trabecular thickness, increase in trabecular separation and a decrease in bone volume which has also been found in this study and an association/correlation established vis-a-vis bone density.
In this study, microarchitectural indices of bone quality were used as measures of bone strength.
A significant correlation was found between bone strength and microstructural indices of bone quality. Although BMD measurements were also found to be significantly associated with bone strength the measure of its significance was much less when compared to bone quality indices.
Bone volume was most significantly associated with bone strength followed by trabecular number.
The order of significance was; bone volume > trabecular number > trabecular separation > trabecular thickness >>> BMD.
As expected, microstructural parameters, that is, bone quality were found to be more correlated with bone strength as compared to bone density measurements.
| Conclusions|| |
While using BMD as a sole predictor of bone strength, bone quality (microstructural indices) also needs to be considered. Bone quality appears to be a better predictor of bone strength as compared to bone density. However, histomorphometric bone quality parameters will require invasive procedures and no other in vivo imaging modality is readily available to quantitatively measure bone microstructure. Finite element analysis, by combining bone geometry with material characteristics to predict bone strength, holds some promise as a biomechanically based technique for fracture assessment, but the same is available only for research purposes. Bone density measurement, on the contrary, is still a rather more available in vivo imaging modality to determine bone strength and still finds its place as a surrogate marker of bone strength. There is a need of development of newer noninvasive in vivo imaging methods that are readily available, that is, micro magnetic resonance imaging, micro-computed tomography (CT), quantitative CT, etc., and assess bone strength independent of BMD and utilize measures for bone quality and these methods should improve the assessment of fracture risk and response to treatment.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]