In today’s lesson we are going to discuss women’s bone health in some detail especially as it relates to osteoporosis. We will also cover bone architecture in some detail.
Recent technological developments are allowing researchers to look deeper into bone architecture and determine the effects of different treatment options for osteoporosis and specifically the relationship between bone density and bone quality. This is an important development for women’s bone health.
For many years bone density has been the key metric to evaluating women’s bone health. But now we are learning more about bone quality. I consider this to be one of the more exciting areas in women’s bone health today.
You are welcome to dive deeper into the topic by going to Today’s Reading Material that I have prepared for you at the bottom of this page!
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Understanding Women’s Bone Health
Women’s bone health is a major health issue. Half of all women over the age of 50 are going to have a fracture in their remaining lifetime.
So today what we’re going to talk about is bone density and bone quality and how it affects someone’s fracture risk. In the people that fracture, what studies have shown is that half of those fractures occur with people that have relatively good bone mineral density scores.
So what is it that makes the difference between fracturing or not fracturing? Most recent studies have shown that it’s someone’s bone quality. Recent diagnostic tools have allowed us to look more deeply into the quality of bone, and that tool is called a peripheral quantitative computer tomography.
Peripheral Quantitative Computer Tomography
Unfortunately it’s expensive, it’s not readily available, there are few out there, and so most of your clients will never have the opportunity to have a PQCT done. But I think it’s very important that you know about bone quality. The quality of bone is defined as a combination of the microarchitecture of the bone and a microstructure of the bone.
The microarchitecture of the bone is the type of rods and cones, the shape of the trabeculae, the thickness of the trabeculae. Whereas the microstructure is the quality of the collagen as well as other bone mineral matrix.
At the 2010 American Society of Bone Mineral Research, there was some really interesting studies that were presented, specifically looking at the use of the peripheral quantitative computer tomography tool to look at whether or not women who fractured had different bone makeup than women of the same bone mineral density and the same age group who didn’t fracture.
Bone Quality and Bone Density
In the women who fractured, even though they had the same bone mineral density and they were of the same age group, it was shown by the peripheral quantitative computer tomography that there were fewer plates and there were fewer connectivities between the plates and rods. Meaning that there was just less trabeculae, less bone, although this was not seen when they did a bone mineral density test.
When they do a bone mineral density test, it strictly just looks at the density of the bone all the way through. Not being able to discriminate between trabecular bone or cortical bone or between thickness of the trabeculae themselves. In the last decade the World Health Organization recognized that their old definition of osteoporosis and osteopenia wasn’t sufficient to identify who should be on medication based on their fracture risk.
They developed FRAX — a questionnaire that looks at a lot of other elements that determines women’s bone health. Beyond their age, their family history, calcium intake, vitamin D intake, and a number of other things such as smoking. I have a page dedicated to the FRAX.
We now have a better understanding of women’s bone health, bone architecture and its relevance to bone quality.
Scientists can now look at the bone architecture through the use of High Resolution peripheral Quantitative Computed Tomography (HR-pQCT). This allows researchers to study the quality of bone structure at the micro level and, hopefully, understand what activities promote improved bone quality and are effective strategies for osteoporosis prevention and treatment.
Two recent studies provide more insight into trabecular architecture as well as the mechanical behavior and fragility of bone. In the following sections, I provide a summary of each of these two studies.
Trabecular Microarchitecture and Mechanical Behavior of L3
At the American Society of Bone Mineral Research (ASBMR) meeting in Toronto in October of 2010, research outlining the contribution of trabecular microarchitecture to the mechanical behavior of L3 was presented. (1)
Before I get into the details of the study and its results, I need to provide some definitions for the reader.
Trabecular Plats and Trabecular Rods — Identification Based on Shape
Trabecula fall into two broad categories based on the shape of the trabecula. These are defined as:
- Trabecular Plates: Trabecular Plates are the trabecula that are thicker and more “plate-like” in shape. In the image to the right, the plates are the wide, flat light colored parts of the bone. Since they are wider and thicker than the rod-like connections, they provide more support and contribute to the overall quality of the bone structure.
- Trabecular Rods: Rods are the trabecula that are “rod-like” in shape. With loss of bone mineral density, the trabecula that are plate-like can become rods as they become thinner. This change can reduce the quality of the trabelula microarchitecture. In the image to the right, the rods are the light colored, thinner rod-like connections.
Bone Architecture — Orientation
Both rods and plates occur in different orientations. The following are the three orientations:
- Transverse — Horizontal alignment
- Oblique — Oblique alignment
- Longitudinal — Vertical alignment
Bone Architecture — Segmentation
Morphological analysis of individual trabeculae segmentation can be broken into the following categories:
- Plate/rod volume fraction
- Axial bone volume fraction
- Plate/rod number density
- Plate/rod thickness
- Plate surface area/rod length
- Plate-plate/plate-rod junction density
An analysis of L3 was undertaken from 21 fresh donors. The average age was 76 years and the group was composed of 10 men and 11 women. Bone mineral content (BMC, g) and bone mineral density, (BMD, g/cm2) were assessed by lateral DXA.
Two vertically oriented virtual biopsies were obtained – one from the anterior vertebral body and one from the posterior vertebral body. Mechanical behavior was assessed using static compression testing involving the following three metrics:
- Failure load (N)
- Stiffness (N/mm)
- Work to Failure (N.mm)
Results & Conclusion
Trabecular architecture was found to have greater deterioration in the anterior versus posterior region. Researchers found that BMD explained up to 44% of the variability in vertebral mechanical behavior. The microarchitecture explained up to 66% of the variability in vertebral mechanical behavior. The combination of bone mass (BMD) with microarchitecture explained up to 86% of the variability in vertebral failure load.
These findings explain why flexion exercises, ADLs and other activities that increase the load on the anterior vertebral body can increase the risk and rate of vertebral fractures.
Microstructural Changes of Trabecular Bone
In another study (2) presented at the same American Society of Bone Mineral Research (ASBMR) meeting in Toronto, researchers explored the microstructural and mechanical changes of trabecular bone in postmenopausal women who had fragility fractures.
Researchers compared 101 control subjects who had not fractured to 68 women who had sustained fractures from a fall or slip from a standing height or lower position. The research team discovered that the DXA scores of both groups were similar. However, the quality of the bone in the fracture group was much lower than that of the group that did not fracture.
The trabecular microstructure and the whole bone stiffness of the women who fractured was lower that that of the control group. The following characteristics of trabecular bone were found among the group that fractured:
- Reduced plate-like bone volume.
- Less plate-like structure.
- Less axially aligned trabecula.
- Longer trabecular rods indicative of more separated trabecula.
- Decreased connectivity between plates and plates and between plates and rods.
Although the BMD of the group who fractured was similar to that of the non-fracture group, the bone quality was the determining factor as to the strength of the bones.
- Wegrzyn J et al. Contribution of Trabecular Microarchitecture and its Heterogeneity to the Mechanical Behavior of Human L3 Vertebra. Univ. Lyon, France and Harvard, Boston. Poster presentation at the 2010 ASBMR Toronto.
- Liu XS et al. Fewer Trabecular Plates and Decreased Connectivity Between Plates and Rods is associated with Reduced Bone Stiffness in Postmenopausal Women with Fragility Fractures. Columbia Univ. NY. Poster presentation at the 2010 ASBMR Toronto.
See you tomorrow.
Physical Therapist, Certified Strength & Conditioning Specialist
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