Fractures of the femoral neck are not simply due to insufficient bone density. Also significant is their nanostructure – the orientation of the collagen fibers that make up bones. This is suggested by research led by EPFL professor and Paul Scherrer Institute group leader Marianne Liebi using a new X-ray technique.When people fracture their hip in a fall, it is very often in the femoral neck –the narrow section of bone directly below the hip joint. This often happens with advanced age, when the bone has lost density. Most often, the femoral neck fractures from the top side, where it is generally much more porous than on the underside.However, this correlation is not always present: sometimes a femoral neck fractures even though it is not porous. Researchers have now discovered the possible cause, through special X-ray analyses using the Swiss Light Source SLS at the Paul Scherrer Institute (PSI) and measurements at the Swedish synchrotron MAX IV: an altered nanostructure of the bone.Arrangement of collagen fibers becomes visibleThe research was led by Marianne Liebi, who is head of the Laboratory for X-ray characterization of materials in EPFL’s School of Engineering and a scientist in the PSI Center for Photon Science. The team used a new imaging technique called small-angle X-ray scattering tensor tomography (SAXS-TT) to examine two bone samples each from 78 different femoral necks. In each case one sample was taken from the top and one from the underside of the same femoral neck.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 fiber are less parallel there than in the lower region. As a result, the bone is more prone to fracture. © Studio HübnerBraunThe analysis 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 hairs –run differently on the upper side than on the underside. While on the underside they lie neatly parallel, allowing them to effectively cushion the forces acting on the femoral neck, 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. The arrangement of fiber and platelets, it is hypothesized, could influence the stability of bones.“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 or not 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 that their work will contribute to a deeper understanding of bone structure in general, as well as to analysis 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,” Liebi. “We are demonstrating what these developments can already achieve today and what direction they can go in the future.”Text: Based on a press release by Jan Berndorff, Paul Scherrer Institute PSI: https://www.psi.ch/en/news/media-releases/nano-insights-into-bone-stabilityReferencesT. Tänzer, T. Kochetkova, A. Baroni, et al. “ Combination of 3D and 2D Small and Wide Angle X-Ray Scattering Imaging Reveals Diminished Bone Quality in the Superior Human Femoral Neck Cortex.” Advanced Materials (2026): e73848. https://doi.org/10.1002/adma.73848