Dual energy x-ray absorptiometry beyond bone mineral density measurement:


vertebral fracture assessment Karen Knapp, Robert Meertens, Lucy Ashton, Susan Hopkins


Osteoporosis is a common musculoskeletal disease in the western world, characterised by reduced bone mineral density (BMD) and micro-architectural deterioration, resulting in an increased risk of fragility fracture1


. Osteoporosis is associated therefore, with


significant morbidity and mortality, and remains a major burden for sufferers and healthcare services2,3


. The incidence of fracture is


considerable, with one in two women and one in five men over the age of 50 sustaining a fracture during their lifetime in the United Kingdom (UK), the majority of which result from osteoporosis4


D criteria6 ual energy x-ray absorptiometry (DXA) is the gold standard for the diagnosis of osteoporosis5 and


provides an important element of fracture risk assessment. DXA is currently the only imaging technique for the diagnosis of osteoporosis which has a wide evidence base and standard diagnostic


. However, the technique is not without its limitations, both in the diagnosis of osteoporosis and in the monitoring of disease progression or therapeutic intervention7


. Firstly, not all patients diagnosed with


osteoporosis using DXA will go on to fracture, whereas conversely the majority of fractures occur in women diagnosed as osteopenic (low bone mass) or as normal by BMD criteria8


or uninterpretable scans to lead to inappropriate management advice is a frequent problem9 DXA scanning technique or interpretation can lead to treatment mistakes10


. The potential for spurious results and incorrect


. Furthermore, the populations


seen by DXA services are changing, with an increased incidence of secondary osteoporosis resulting from a multitude of causes such as oncological treatments, glucocorticoid use, transplants, gastrointestinal


-48- disorders, neurological disorders and diabetes5,11-17 . . Different clinical populations are at risk of fracture at


different BMD levels and therefore alternative diagnostic thresholds have been developed for particular populations17,18


Changing populations and increasing levels of obesity19 have also had an impact on services. Obesity


has generally been considered as protective against osteoporosis, largely due to the positive correlation between body mass index and BMD20


and as such, low levels of obese patients were generally seen in DXA


services. However, obesity is now known to be related to an increased fracture risk and this is likely to lead to increased numbers of obese patients being seen within DXA services21,22


. Obesity can increase precision


errors in both bone and body composition measurements when using DXA, and this provides challenges for longitudinal monitoring of obese patients using this modality23,24


. Since DXA, despite its limitations, is


currently the most available and appropriate tool for diagnosis of osteoporosis, methods to improve the prediction of fracture using this technique have been widely researched3


. . Clinical risk factors (CRFs) have


been demonstrated to predict fracture risk and the opportunity is available to combine BMD results with assessment tools for CRFs, such as FRAX, which provides more accurate fracture risk prediction and can provide a ten year fracture risk assessment3,8


Fracture prediction can be further improved through identifying the presence of vertebral fractures, a


strong predictor of future fracture. DXA affords the ability to undertake imaging for vertebral fractures, while still maintaining a low radiation dose. As a result, the use of vertebral fracture assessment (VFA) is growing in the UK but is still limited, with not all departments having the resources or pathways to implement this useful tool. In some patient groups such as women over 70 and men over 80 with osteopenia25


VFA is an


important addition to standard lumbar spine and proximal femur BMD measurements, and one which can help to optimise therapeutic interventions26


. Furthermore, in some patients where standard DXA


measurement sites are impossible due to fractures, surgical implants or other artefacts, the combination of VFA, with clinical risk factors can provide a better assessment of fracture risk than clinical risk factors alone.


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