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Torne Tänzer and Marianne Liebi at the Swiss Light Source SLS at PSI. Here, they were able to visualise the nanostructure of femoral neck bone material for the first time. This could help to understand why this part of the femur fractures relatively frequently.
Photo Credit: © Paul Scherrer Institute PSI/Markus Fischer
Scientific Frontline: Extended "At a Glance" Summary: Nano-Insights Into Bone Stability
The Core Concept: Femoral neck fractures are driven not only by reduced bone density but also by critical structural abnormalities at the nanoscale, specifically the disordered orientation of collagen fibers and mineral platelets.
Key Distinction/Mechanism: While traditional diagnostics focus primarily on bone porosity and overall mass, this research demonstrates that the physical arrangement of collagen fibers (disordered versus parallel) and calcium phosphate mineral platelets significantly dictates a bone's mechanical flexibility and fracture resistance.
Major Frameworks/Components:
- Small-Angle X-ray Scattering Tensor Tomography (SAXS-TT): A novel imaging methodology combining high-resolution small-angle X-ray scattering with 3D tomography to visualize nanoscale orientations.
- Collagen Fibers: Structural protein threads that run parallel on the bone's underside to cushion forces but crisscross on the upper side, increasing rigidity and fracture risk.
- Mineral Platelets: Tiny lamellae of calcium phosphate located between collagen fibers that exhibit irregular shapes and arrangements in fracture-prone bone sections.
Branch of Science: Biophysics, Materials Science, and Orthopedics.
Future Application: These findings lay the groundwork for mechanical stress testing that can accurately predict aging-related fracture risks, alongside the development of advanced diagnostic imaging capabilities for clinical orthopedic use.
Why It Matters: By explaining why the femoral neck can fracture even when bone density appears normal, this research paves the way for better preventative care, earlier diagnosis of structural degradation, and deeper insights into fundamental bone mechanics.
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| Tensor tomography of a femoral neck: the sample taken from the upper region contains more dark grey and red values rather than light grey ones. This means that the collagen fibres are less parallel there than in the lower region. As a result, the bone is more prone to fracture. Image Credit: © Studio HübnerBraun |
Fractures of the femoral neck are not simply due to insufficient bone density. Their nanostructure—the orientation of the collagen fibers that make up bones—is also significant. This conclusion is supported by research conducted by scientists at the Paul Scherrer Institute (PSI) using a new X-ray technique.
When people fracture a hip in a fall, the injury frequently occurs in the femoral neck—the narrow section of bone directly below the hip joint. This typically happens in advanced age, when bone density has decreased. Most often, the femoral neck fractures from the top side, where it is generally much more porous than on the underside.
This correlation, however, is not always present; sometimes a femoral neck fractures even when it is not porous. Through specialized X-ray analyses using the Swiss Light Source (SLS) at PSI and measurements taken at the Swedish synchrotron MAX IV, researchers at PSI have discovered a possible cause: an altered bone nanostructure.
New X-Ray Technique Offers Detailed Insights
The team, led by Marianne Liebi, a scientist in the PSI Center for Photon Science, used a novel imaging technique to examine two bone samples each from 78 different femoral necks. In each instance, one sample was taken from the top and one from the underside of the same femoral neck. The team obtained the samples from the University of Bern, whose experts participated in the analysis as part of a joint research project. The method is called small-angle X-ray scattering tensor tomography, or SAXS-TT. It combines the analysis of so-called small-angle scattering signals from a high-resolution X-ray image with 3D tomography—that is, imaging from different angles. This method has been developed at PSI over the past ten years and tested for the analysis of various materials, including bone.
Arrangement of Collagen Fibers Becomes Visible
The analysis of bone samples from 78 different femoral necks revealed that, in addition to the lower bone density on the upper side of the femoral neck, another factor stands out: the collagen fibers—which make up bones and are a thousand times finer than human hair—run differently on the upper side than on the underside. While they lie neatly parallel on the underside, allowing them to cushion the forces acting on the femoral neck effectively, they appear more disordered on the upper side, running at an angle or even crisscrossing. This makes them less flexible. "Furthermore," says lead author Torne Tänzer, a doctoral candidate in Liebi’s research group, "the mineral platelets are less regularly arranged and differently shaped." The mineral platelets of a bone are tiny lamellae of calcium phosphate that lie between the collagen fibers and stabilize them.
Researchers hypothesize that the arrangement of fibers and platelets could influence bone stability. "We now want to investigate this hypothesis in further studies by conducting mechanical stress tests on femoral necks with different structures," says Tänzer. This should reveal whether an irregular structure actually increases the risk of fractures. "We may then also be able to determine to what extent such changes in nanostructure are related to age."
The researchers hope their work will contribute to a deeper understanding of both general bone structure and analytical methods. Furthermore, it could advance fundamental research into bone mechanics. "Methods for examining biological materials at the nanoscale, both structurally and mechanically, are constantly being developed," says Marianne Liebi. "We are demonstrating what these developments can already achieve today and what direction they can go in the future."
Faster Imaging Thanks to SLS Upgrade
In future studies, the researchers will benefit from the recent SLS upgrade. Its entire electron storage ring was replaced with more than a thousand new, high-precision magnets, thus increasing the intensity and brilliance of the X-ray light source many times over. This makes it possible to produce significantly more detailed images than before while considerably reducing measurement time.
"We were able to scan bone samples in full 3D from only two of the 78 femoral necks because, with the previous technology, this was simply very time-consuming and incredibly complex," Tänzer says. The 3D tomography required a full day per scan, while the 2D thin-section measurements, which were performed during the SLS upgrade at the Swedish synchrotron MAX IV, took only 20 minutes. With these few 3D examples, the researchers were able to draw conclusions about the other samples that were viewed only in two dimensions, thus improving the interpretation of the 2D data. "With the upgraded SLS, we will now be able to analyze many more samples in 3D. This will significantly boost our ability to gain new insights."
Published in journal: Advanced Materials
Authors: Torne Tänzer, Tatiana Kochetkova, Arthur Baroni, Mathieu Simon, Mads Carlsen, Santiago Fernandez Bordin, Manuel Guizar-Sicairos, Philippe Zysset, and Marianne Liebi
Source/Credit: Paul Scherrer Institute | Jan Berndorff
Edited by: Scientific Frontline
Reference Number: biph070926_01