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The averaged score for bone strength used in clinics may not be enough to predict hip-fracture risk, scans from 7,000 UK Biobank participants have shown.

Summary

A ‘bone-age map’ can reveal weak spots in someone’s hip – something that’s impossible with the currently clinical assessment. The map was created with x-ray scans from more than 13,000 women, including 7,000 UK Biobank participants. It could help doctors to prevent hip fractures in older women with osteoporosis, who are at particular risk of these painful injuries.

Someone’s ‘bone age’ could hint at weak spots in the hip. A way to map bone age, developed with X-ray scans from more than 13,000 women including 7,000 UK Biobank participants, could help doctors to pinpoint weak areas in the thigh bone and prevent fractures.

In the clinic, they use a single number – average BMD [bone-mineral density] – to diagnose osteoporosis. It is easy to calculate, easy to measure. But this study showed that distribution is important, even with the same BMD.

Associate Professor Yoshito Otake, Nara Institute of Science and Technology (NAIST), Japan

Hip fractures – breaks in the femoral neck, the upper thigh bone close to where it meets the pelvis – are acutely painful. Older women are at particular risk because they tend to be more affected by bone-weakening osteoporosis because of the hormone changes that happen during menopause. If clinicians spot signs of osteoporosis, they can advise on bone-strengthening medication, exercise or food.

“In the clinic, they use a single number – average BMD [bone-mineral density] – to diagnose osteoporosis,” explains biomedical imaging specialist Yoshito Otake from the Nara Institute of Science and Technology in Japan, who is independent of the study’s research team. BMD is assessed with a bone-density scan called a dual-energy x-ray absorptiometry (Dexa). “[BMD] is easy to calculate, easy to measure. But this study showed that distribution is important, even with the same BMD.”

An atlas of bone strength

The problem with a single score is that the different regions in the femoral neck weaken at different rates, explains Jeremy Mark Wilkinson from the University of Sheffield, UK, who led the study. His team mapped bone density in more than 13,000 white women’s Dexa scans to create a detailed bone-age atlas for this group. This helps to pinpoint where and when the femoral neck’s density changes, from age 20 to 97.

When Wilkinson’s team compared two 75-year-old women with almost identical BMD scores, one was at higher risk of breaking a hip because her bone was weaker in an area where it matters. “With standard Dexa femoral neck assessments you just can’t do that,” Wilkinson says.

The way Wilkinson’s team analysed the Dexa images isn’t new, Otake says, but they apply it to the huge amount of imaging data for the first time. “They brought it to real world data – it’s very convincing.”

They brought it to real world data – it’s very convincing.

Associate Professor Yoshito Otake, Nara Institute of Science and Technology (NAIST), Japan

Wilkinson hopes to test whether his method could predict the types of fractures people might experience. This could allow health services to have the right clinicians and equipment in place because “certain types of fracture we fix with plates and screws, and others [need a] part or total hip replacement”, he explains.

Otake points out that despite its potential advantages, bone-age mapping isn’t going to be used in clinics anytime soon. “The single number is already established, based on a lot of evidence,” he explains. “We need to accumulate more evidence on the relationship between [bone density] distribution and fracture.”

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