Older people’s risk of broken bones could depend on whether their bones are flexible

Osteoporosis drugs designed to salvage crumbling bones may actually make them weaker, research suggests.

Imperial College London experts compared the hip bones of dead people who had donated their bones for science.

They found those who had never once had a broken bone had more flexible collagen and mineral structures, which are the building blocks of bones.

Their bones were more able to flex and absorb the shock of falls than people who had stiffer bones which snapped more easily, scientists say.

Some of the donors with hip fractures were taking drugs called bisphosphonates for osteoporosis, a condition that causes bones to deteriorate and become extremely fragile.

The drugs, including Fosamax, Binosto and Pamidronate, slow the speed at which bone degrades to slash the risk of fractures. 

But donors who had been taking bisphosphonates for between one and 13 years had lower tissue strength and flexibility than those who had not.

Academics led by Dr Shaocheng Ma admitted they were surprised by the finding, which was published in the journal Scientific Reports. 

It suggests that although bisphosphonates retain bone density, the benefits may be offset by a reduction in flexibility, which makes bones more likely to break.

Figure show around three million people in the UK, 10million in the US and 200million worldwide live with osteoporosis. 

The condition, which tends to be caused by hormone imbalances, makes bones deteriorate from the inside out and makes them much more likely to fracture. 

The NHS claims patients can suffer a broken rib simply from coughing or sneezing. Broken wrists are the most common injury. 

Doctors usually diagnosed the condition using bone density scans, but some people whose bones appear normal on these scans are still unusually prone to breaks.  

This is because several other factors – such as someone’s age or whether they have broken the bone before – are as important as bone density. 

To find out more, the researchers at Imperial looked to the building blocks of bones – stiff minerals surrounding flexible collagen fibrils.  

The scientists split a group of 30 people into those who never broke a bone; those who broke bones and took biphosphonates; and those who broke bones but didn’t take the drugs.

They used super strength X-rays that show bone flexibility extremely close-up. 

Donors who had never broken their bones were more likely to have flexible collagen and minerals under weight, compared to those who had suffered fractures.  

In those who had suffered fractures, the mineral broke away from the collagen at much lower forces of weight.

This was irrespective of whether they had taken bisphosphonate drugs, which can be given as tablets or injections.

The bones may have fractured because the tissue was too inflexible and could not deform to absorb energy during a bump or fall, the researchers said. 

The findings suggest doctors should look not only at bone density, but also bone flexibility, when deciding how to prevent bone breakages. 

Study co-author Dr Ulrich Hansen 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 flexibility could be just as important as density in preventing fractures.’ 

The findings are important for patients given bisphosphonate, designed to prevent bones breaking down by increasing bone mass and mineral density. 

Donors with hip fractures who had received bisphosphonates for between one and 13 years had the lowest tissue strength and flexibility. 

But the study did not say which drugs the patients had been taking specifically.  

Falls are common in Britons over the age of 65, and are the most common cause of injury related deaths in people over the age of 75.

There is a concern that falls can lead to fractured or broken bones, which can cause a person to need extra support and feel as if they have lost their independence. 

Co-author Dr Richard Abel said: ‘We were surprised to see 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 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.’

Charities say bisphosphonates – also given to people with Paget’s disease and some forms of cancer to stop it spreading to the bones – can cause fractures in the femur, in extremely rare cases. 

The risk appears to increase the longer a patient has been on the drugs, according to Versus Arthritis.

In some bisphosphonate users, the drug may bind itself to and harden minerals that are important for bone flexibility, the researchers said.

However, the findings could also be a result of the patients’ bones being significantly more osteoporotic in the first place.  

Lead author Dr Shaocheng Ma said: ‘It’s possible that the amount of mineral strain is key in setting off the fracture process. 

‘However, in patients who have taken bisphosphonates for a long time the mineral could become too stiff, causing it to break away from the collagen. 

‘This releases the collagen and allows it to stretch uncontrollably, which then results in a fracture.’

The researchers say that people who are taking bisphosphonates should continue to follow the advice of their doctors.