What is does the trabecular bone score reported on your DXA scan mean?

A trabecular bone score (TBS) is something you might see on your DXA scan, which you may have had to check your bone density (BMD). 

If you want to learn more about DXA scans, check out our blog post on those here. 

TBS is a measurement that comes from the lumbar spine (lower back) and looks at bone microarchitecture, rather than its density. 

Bone microarchitecture refers to the tiny internal structure and organisation of bone. Essentially, how the bone is built at a microscopic level.

• Bone density (BMD) tells us roughly how much material there is actually making up our bones.
• Bone microarchitecture tells us how that material is arranged, that is, the thickness, number and connectivity of the internal struts and plates that give the bone its strength.

Inside our bones, particularly trabecular (spongy) bone, there is a complex network of tiny structures called trabeculae. Healthy bone has a well-connected, relatively robust network.

With osteoporosis and ageing, changes can occur such as:

• trabeculae becoming thinner
• some trabeculae being lost
• the connections between them becoming weaker or disrupted
• the overall internal structure becoming less able to withstand loading.

TBS analyses the texture of the lumbar spine image from your DXA scan to provide an indirect measure of trabecular bone microarchitecture. The measurement is taken at the lumbar spine as that is where the degraded microarchitecture is likely to be the most significant.  

Why could TBS be important?

TBS can be important, because bone density does not always give the full picture of how at-risk one is of sustaining a fracture. Many low-trauma fractures occur in people who have osteopenia, but not osteoporosis.  

Incorporating a trabecular bone score alongside bone density can provide a more accurate fracture risk assessment calculation. A degraded TBS can identify additional fracture risk that may not be captured by BMD alone. This can be particularly useful when interpreting a DXA result in someone whose BMD is in the osteopenic range.

You will see the number reported as something such as:

TBS: low (severely degraded), medium (partially degraded) or high (minimal degraded). 

You may then also see a ‘TBS adjusted FRAX’, which indicates that when calculating your risk of sustaining a fracture in the next 10 years, the technicians have included your BMD as well as your TBS scores (as well as other risk factors included in that calculation). 

In people with certain health conditions, TBS may be particularly useful alongside BMD, as bone mineral density alone may not fully reflect fracture risk.

This may be especially relevant for people with secondary osteoporosis. Secondary osteoporosis occurs when bone loss is caused or contributed to by another factor, such as an underlying health condition or certain medications. In contrast, primary osteoporosis develops in association with factors such as ageing and hormonal changes, including the decline in oestrogen after menopause.

Examples of situations where TBS may provide additional information alongside BMD include:

• Long-term glucocorticoid use
• Chronic kidney disease
• Endocrine disorders
• Some inflammatory or rheumatological conditions
• Aromatase inhibitor treatment
• Other causes of secondary osteoporosis

In some of these conditions, bone microarchitecture may deteriorate even when BMD does not appear particularly low. TBS can provide additional information about bone health that may help clinicians assess fracture risk more comprehensively.

Treatment considerations

As always, exercise is recommended as a part of osteoporosis or osteopenia management, regardless of TBS score. It is uncertain whether exercise can change a degraded TBS. 

TBS can change in response to osteoporosis medications, although the response varies depending on the treatment.

Antiresorptive medications such as bisphosphonates and denosumab tend to preserve or modestly improve TBS, with changes generally smaller than those seen in BMD.

Anabolic medications, which stimulate new bone formation, tend to produce larger and earlier improvements in TBS. The statement suggests TBS may therefore be useful alongside BMD when monitoring treatment, particularly with anabolic therapies.

Not all machines are able to perform a TBS reading, so it is worth enquiring when booking your scan if it is something you can access.  

Take homes

If you are interested in learning more about your TBS score, or wonder if it something that might be relevant for you, it is worth discussing with your GP, or even more appropriate, your endocrinologist, who is likely to be able to provide an in depth assessment of its relevance to you and your bones.