Nanoscale Bone Inflexibility Hip Fracture Risk Factor

It is not just bone density that is an important hip fracture risk factor, Imperial College London researchers say. Nanoscale bone inflexibility may also play a role.

The researchers in the study, “Nanoscale mechanisms in age-related hip-fractures,” which was published online in Scientific Reports on August 26, 2020, set out to investigate why some people who have healthy bones on DEXA [dual-energy X-ray absorptiometry] scans still are at increased risk of hip fracture.

“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,” said study co-author Ulrich Hansen, Ph.D., of Imperial’s department of Mechanical Engineering.

To examine bone flexibility at the nanoscale, they used high-energy intense beams of X-rays. In particular they were looking at how the collagen and minerals within bone flex and then break apart under a load.

The researchers analyzed bone tissue samples of three groups of donors: those who had not any fractures, 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.

Overall, the donors without fractures were more likely to have flexible collagen and mineral nanostructure than those with a hip fracture. In those with fractures, the mineral broke away from the collagen at lower forces.

They also found that bisphosphonate, a common treatment for osteoporosis, appears to lower tissue strength and nanoscale flexibility in people with hip fractures compared to people with hip fractures not on the treatment and the control group.

The reasons for this are unclear, the researchers say and require more study.

“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 benefit 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,” explained Richard Abel, M.D., co-author from Imperial College London’s department of Surgery and Cancer.

“Perhaps we need to build on the existing treatment framework to add new diagnostics, therapies and follow-ups that address nanoscale bone health—and address the collagen, not just the mineral. That way we can treat everyone in the best possible way.”

The researchers hope their findings help develop more preventative treatments of bone fractures.