Nanoscale bone inflexibility link to hip fracture risk

Flexibility and density in the bone nanostructure need to be assessed together to estimate how likely someone is to suffer fractures, according to new research.

Researchers at Imperial College London and published in Scientific Reports, studied why people whose bones seem healthy on DEXA scans are more likely than others to suffer fractures.

The research team analysed the stiff minerals surrounding flexible collagen fibrils, using high-energy intense beams of X-rays generated by Diamond Light Source to examine bone flexibility at the nanoscale.

This enabled them to assess how the collagen and minerals within bone flex and then break apart under load in the nanostructure of hip bone samples.

The researchers compared the behaviour of the bone tissue samples under load between three groups of donors: those who had not suffered a hip fracture, or any other fracture; those without a bisphosphonate treatment history who had suffered a fractured hip; and those with a bisphosphonate treatment history who had suffered a fractured hip.

They found that donors with hip fractures who had received bisphosphonates for between one and 13 years had lower tissue strength and nanoscale flexibility than the untreated fracture donors and a control group.

Donors without fractures were more likely to have flexible collagen and mineral nanostructure than those with who had suffered fractures. The collagen and minerals were less flexible under load in patients with fractures, irrespective of bisphosphonate treatment.

The bones may have fractured because the tissue was too inflexible and could not deform to absorb energy during a bump or fall, highlighting the importance of flexibility in the collagen and minerals of bone.

They add that flexibility at the nanoscale could be important in predicting future bone fractures and a target for new treatments.

Study co-author Dr Ulrich Hansen, of Imperial’s Department of Mechanical Engineering, said: “We tend to think of our bones as solid, hard support structures, but flexibility appears to be extremely important in bone health. If bones are too hard, they are less able to absorb impact and more likely to break. Our study suggests that flexibility could be just as important as density in preventing fractures.”

Co-author Dr Richard Abel from the Department of Surgery and Cancer added: “We were surprised to see that bisphosphonate users seemed to have less flexible bone nanostructures. Perhaps after a long period of treatment in some patients, there is a loss of flexibility at the nanoscale that offsets some of the strength benefits from increases in bone density. More research is needed to determine exactly why this is and how this could affect clinical practice in long-term users.”

The researchers say anyone taking bisphosphonates should continue to follow the advice of their doctors and seek a review of treatment after five and 10 years as per clinical guidelines.

Ma S, Goh EL, Tay T et al. Nanoscale mechanisms in age related hip fractures. Scientific Reports 26 August 2020

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