The role played by Dual Energy X-Ray Absorptiometry (DXA) technology in diagnosing and treating osteoporosis

Osteoporosis is recognised as one of the most significant public health issues because of the substantial mortality and high costs associated with its complications. Some examples include fractures of the spine, hip, forearm or other parts of the skeleton. Fragility fractures particularly trouble elderly women, with some studies showing that nearly one in two women might suffer an osteoporosis-related fracture at some point in their life. Great attention is given by medical institutions to hip fractures as they incur the most medical expenses. However, other fractures like that of the spine or forearm can also cause significant morbidity, and both vertebral and hip fractures raise the probability of death, along with making the patient increasingly dependent on caregivers for even the most basic activities of their daily life.

While there was always an awareness of the mortality and morbidity linked to fragility fractures, real progress only came about with the ability to diagnose osteoporosis before a fracture even occurred, along with the development of effective treatment. Bone mineral density (BMD) measurement played a critical role in both these advancements. Until the middle of the 1980s, bone mineral density measurement was mainly used for research purposes. It was only after the arrival of dual energy x-ray absorptiometry (DXA) scanners in the year 1987 that they became commonplace in medical clinics. Additional milestones include a publication from the World Health Organization that defined osteoporosis in postmenopausal white women as a BMD T-score at the hip, forearm or spine of less than -2.5; the Fracture Intervention Trial confirming that fractures can be prevented with bisphosphonate treatment and a publication that showed how bisphosphonate treatment helps prevent bone loss. After that, a large number of trials have proved the effectiveness of bisphosphonates (BPs), recombinant human parathyroid hormone (PTH), strontium ranelate and selective oestrogen receptor modulators (SERMs) in preventing the occurrence of fragility fractures.

In the 21st century, bone mass density measurements play a vital role in evaluating a patient’s risk of osteoporosis and suggesting anti-fracture treatment to be used at the appropriate time. Generally, a preferable testing method is using central skeleton DXA scans to measure the bone mass density of the hip and lumbar spine. Central DXA scans serve three major roles – diagnosing osteoporosis, assessing patients’ risk of a fracture, and monitoring their response to treatment. Central DXA is preferred because hip bone mass density is the most reliable way to measure hip fracture risk prediction, the spine is used to monitor the treatment more often than not, and the broad consensus that hip and spine bone mass density measurements in postmenopausal white women should be interpreted along the WHO provided definition of both osteopenia and osteoporosis.

A T-score is calculated by considering the difference between a patient’s bone mass density versus the mean bone mass density in an average healthy adult, matching them along gender and ethnic group, and considering the difference to the population standard deviation (SD).

A central DXA has several advantages such as –

• A general consensus that bone mineral density results can be understood with WHO T-scores
• Proven ability to detect the risk of bone fracture
• Basis of the new WHO algorithm used to predict fracture risk
• Effective at targeting treatments for anti-fracture
• Helpful in monitoring patients’ response to treatment
• Good accuracy
• Stable calibration
• Short scan time required
• Makes rapid patient setup possible
• Low amount of radiation dose administered
• Reliable reference range available for comparison

Along with central DXA for hip and spine measurements, other types of machines are also available in the bone densitometer devices market. Some examples are peripheral DXA machines for the forearm, quantitative computed tomography (QCT) for the hip and spine, and quantitative ultrasound (QUS) devices for the heel and other sites on the periphery. In theory, pDXA and QUS systems offer a cost-effective, quick and easy method of evaluating a skeleton which should make them attractive for widespread use. In reality, however, these alternate measurements correlate rather poorly with DXA and their lack of agreement with it has proved a major challenge in reaching a consensus on their widespread adoption.