Screening for Osteoporosis -Making an Informed Choice of DXA or Calcaneal QUS

Abstract

Osteoporosis is characterized by a reduction in bone mass or bone mineral density and an increase in fracture risk. As it runs a silent course before presenting with a fracture, the importance of screening especially of risk groups for timely diagnosis and treatment, cannot be overemphasized. Often in developing countries, where access to labs and devices like DXA may be limited, onsite high-volume screening can contribute significantly in diagnosing Osteoporosis cases and contribute towards reduction in morbidity and economic burden due to development of fractures. Though DXA is the gold standard for Osteoporosis diagnosis, recently calcaneal quantitative ultrasound is emerging as a convenient, portable, low cost and radiation free device for in-clinic or onsite screening. Therefore, the differences in parameter interpretation and evaluation, along with relative advantages and disadvantages of using calcaneal QUS over DXA should be well understood before making an informed choice.

Full text

ARC Journal of Orthopedics
Volume 4, Issue 1, 2019, PP 9-13
ISSN 2456-0588
DOI: http://dx.doi.org/10.20431/2456-0588.0401003
www.arcjournals.org
ARC Journal of Orthopedics Page | 9
Screening for Osteoporosis – Making an Informed Choice of DXA
or Calcaneal QUS
Varsha Narayanan*
Health and Pharmaceutical Consultant, Dr Varsha’s Health Solutions, Andheri west, Mumbai India
1. INTRODUCTION
Osteoporosis is a disease characterized by low
bone mass (bone mineral density- BMD),
decreased quality of bone tissue, and increased
risk of fracture. [1] The loss in bone density
usually continues silently over many years and a
fracture may often be the first clinical
manifestation usually of advanced disease by that
time.
The common Osteoporotic fractures sites include
the hip, spine, wrist, and shoulder. [1, 2]
Osteopenia refers to decreased bone mineral
density (BMD) as compared to normal peak
density, but not low enough to significantly
increase fracture risk and be considered as
Osteoporosis, however it is a risk factor for
Osteoporosis. [1] A single cause of Osteoporosis
is not established therefore risk factor
identification often helps in selecting screening
groups to facilitate timely diagnosis. (Table 1).
[3-12]
Over 200 million people worldwide, and
approximately 30% of all postmenopausal
women have Osteoporosis in the United States
and in Europe. [13] In India more than 50 million
people are either osteoporotic (T-score lower
than-2.5) or have low bone mass (T-score
between-1.0 and-2.5), and studies indicate that
Osteoporosis and Osteopenia or low bone mass
may occur at a relatively younger age in Indian
population. [14] Screening has an important
place in early diagnosis, care and treatment of
Osteoporosis.
However, for mass screening or camps, cost and
portability of equipment are realistic challenges
and limitations. Though Dual-energy X-ray
Absorptiometry (DXA or DEXA) remains the
gold standard of diagnosis of Osteoporosis, the
calcaneal Quantitative Ultrasound (QUS) has
been increasingly used in screening camps due to
it lower cost, easy transportation and
convenience. Therefore, it becomes pertinent to
understand how the calcaneal ultrasound
compares to the standard DEXA, and what
should be its rational and scientific place for
measuring bone mineral density (BMD) for the
screening and diagnosis of Osteopenia and
Osteoporosis.
*Corresponding Author: Varsha Narayanan, Health and Pharmaceutical Consultant, Dr Varsha’s Health
Solutions, Andheri west, Mumbai India. Email: drvarsha@rediffmail.com
Abstract: Osteoporosis is characterized by a reduction in bone mass or bone mineral density and an increase
in fracture risk. As it runs a silent course before presenting with a fracture, the importance of screening
especially of risk groups for timely diagnosis and treatment, cannot be overemphasized. Often in developing
countries, where access to labs and devices like DXA may be limited, onsite high-volume screening can
contribute significantly in diagnosing Osteoporosis cases and contribute towards reduction in morbidity and
economic burden due to development of fractures. Though DXA is the gold standard for Osteoporosis diagnosis,
recently calcaneal quantitative ultrasound is emerging as a convenient, portable, low cost and radiation free
device for in-clinic or onsite screening. Therefore, the differences in parameter interpretation and evaluation,
along with relative advantages and disadvantages of using calcaneal QUS over DXA should be well understood
before making an informed choice.
Keywords: DXA, DEXA, QUS, Osteoporosis, T score, BMD, Fracture

Screening for Osteoporosis – Making an Informed Choice of DXA or Calcaneal QUS
ARC Journal of Orthopedics Page | 10
Table1. Risk factor identification for Osteoporosis screening
Risk
Details
1
Age[3]
 90% hip fractures occur in people aged ≥50 years. (independent risk factor)
 Bone mineral density reduces with age.
2
Female gender[4]
 Post-menopausal women are more susceptible to bone loss than men due to reduced
estrogen hormone which is important in bone formation.
 Women are more likely to sustain an osteoporotic fracture than men with a 40-50%
lifetime risk in women, compared to 13-22% in men
 Peak bone mass reduced by late menarche.
 Premature menopause, especially before the age of 45, is a strong determinant of bone
loss and increased risk of fracture [1]
 Hysterectomy, with removal of ovaries, increases the risk for Osteoporosis
3
Ethnicity[5]
 Osteoporosis is more common in Caucasian and Asian populations
 Lower incidence of Osteoporosis and hip fractures in black than in white people
4
Family history[6]
 Parental history of fracture (especially hip fracture) is associated with increased risk
of fracture (independent of BMD)
5
Past fracture
history[7]
 A previous fracture increases the risk of any fracture by 86%,
 Double risk (1.86 times) of a second fracture
6
Systemic
comorbidities and
conditions[8]
 Some systemic conditions constitute secondary risk factors that directly or indirectly
affect bone remodeling, mobility and balance, and increased risk of falling and
sustaining a fracture
 Like Asthma, Crohn’s or celiac disease, Rheumatoid arthritis, Hematological
disorders or Malignancies, Hypogonadal states, Endocrine disorders like Cushing’s
syndrome, Hyperparathyroidism, Diabetes and Chronic Renal Failure.
7
Drugs[9]
 Some drugs directly weaken bone or increase fracture risk due to fall or trauma.
 Like Corticosteroids, Immunosuppressant (calcineurin inhibitors), L-Thyroxine,
Progesterone treatment, Aromatase inhibitors, Certain Antipsychotics, Antiepileptics,
Lithium, Methotrexate, Heparin, Antacids and Proton Pump Inhibitors
8
Smoking[10,11]
 Associated with lower BMD, reduced body weight, earlier menopause, increased
metabolic breakdown of exogenous estrogen in women.
 BMD 2% lower in smokers than in non-smokers for each 10-year increase in age (6%
at age 80 years)
 Cigarette smoking is independent risk factor for hip fracture
9
Physical
Inactivity[12]
 Physical loading and mechanical stress increase BMD
 Certain forms of exercise may retard bone loss.
 Epidemiological relationship exists between physical inactivity in elderly and the risk
of hip and vertebral fracture.
2. SCREENING AND DIAGNOSING
OSTEOPOROSIS – CALCANEAL QUS OR
DXA
Dual-energy X-ray absorptiometry
(DXA, previously DEXA) measures bone
mineral density (BMD). Two X-ray beams, with
different energy levels, are aimed at the
patient's bones (hip and lumbar spine) and
the bone mineral density (BMD) is determined
from the absorption of each beam by bone after
soft tissue absorption is subtracted.[15] Dual-
energy X-ray absorptiometry is the most and
thoroughly studied bone density measurement
technology and is the gold standard for
measuring BMD and diagnosing Osteoporosis.
Bone densities are expressed as T score or Z
score. [16] T score expresses BMD in
comparison to a young adult of the same gender
with peak BMD. A normal T score is ≥ -1.0, low
bone density (Osteopenia) is between -1.0 and -
2.5, and Osteoporosis is ≤ -2.5. Z score expresses
BMD in comparison to the average BMD of a
male or female of their age and weight. Severe or
established Osteoporosis refers to a T-score more
than -2.5 standard deviations below the young
adult female reference mean in the presence of
one or more fragility fractures.
Quantitative ultrasound (QUS) has recently
emerged as a convenient and popular screening
tool for Osteoporosis, because it is portable,
easier to handle, lower in cost and does not emit
ionizing radiation, especially in developing
countries where dual-X-ray absorptiometry
devices are less accessible to the general
population.[17] QUS employs high frequency
sound waves with an emission and receiver
probe, to determine bone quality, bone
microarchitecture and mechanical parameters by
studying speed (Speed of Sound - SOS) and

Screening for Osteoporosis – Making an Informed Choice of DXA or Calcaneal QUS
ARC Journal of Orthopedics Page | 11
attenuation (Broadband Ultrasonic Attenuation-
BUA) of ultrasonic waves. Sophisticated devices
use additional QUS indices like eBMD
(Estimated Bone Mineral Density) which can be
calculated from the SOS and BUA.18
Longitudinal transmission is more often used,
and the preferred, most researched and
recognized bone segment measured is the
calcaneus as it consists of 95% trabecular bone
and has two lateral surfaces to facilitate the
movement of ultrasound through it.
In the classification of low bone density using
DXA, T-score with cut-off points of ≤-1.0 SD for
Osteopenia and ≤-2.5 SD for Osteoporosis are
used, however, simply applying the DXA cut-
offs in QUS measurement can significantly
underestimate the true prevalence of
Osteoporosis. This was seen in a Korean study
(Hologic Sahara QUS device - eBMD) where
applicable T-scores for women and men were -
2.25 and -1.85, respectively as compared to T-
score of -2.5, the WHO threshold for
Osteoporosis. [19] Another device (Osteometer
DTUone) has T score cut offs of -1.45 and -2.10
for BUA and SOS. [20] Reference ranges maybe
affected by ethnicity (Caucasian reference BMD
range is higher than Asian) and gender. In India
and Asia, the light weight Furano CM-200 QUS
using SOS parameter is commonly used in
Osteoporosis screening camps.
The optimal T-score threshold for Osteoporosis
diagnosis in QUS was calculated in eight studies
where the value varied between -1 and -2.6, with
a DXA T-score of -0.9 to -3.3 with one study
proposing a T-score threshold as low as -3.65.
[21] In most of the studies the QUS T score cut
off was either higher (average -2.2+/-0.8) or
equal to DXA cut off which correlates with other
studies above.
Therefore, the QUS and DXA measurements
should not be compared with each other using the
same T-score criteria, because of different bone
properties measured and different reference
populations. A good predictive relationship
between hip bone mineral density, as estimated
by calcaneal QUS, and direct DXA measurement
has been seen, however this correlation decreases
for lumbar spine. [22, 23] In patients with
Osteoporosis determined by calcaneal QUS or
DXA in a Brazilian study, complementing with
X-ray was suggested for predicting vertebral
fracture. [24]
Based on the population data, investigators have
found that –1.455 for the right QUS T score and
–1.48 for the left QUS T score achieved adequate
screening parameters to identify Osteoporosis.
[25] Cutoff scores produced a sensitivity of 41%
and a specificity of 86.6% for the right QUS T
score and a sensitivity of 51.3% and a specificity
of 83.3% for the left QUS T score. With a higher
QUS T score cut-off of -1.25, sensitivity was
higher at 80.4% with a specificity of 59.7% as
seen in a study from China. [26] A meta-analysis
of 25 studies to assess the accuracy of
quantitative ultrasonography compared with
DXA in identifying patients with Osteoporosis,
various quantitative ultrasonography index
parameter cutoffs were used, and the results
varied widely in sensitivity and specificity for
identifying individuals with a T-score of -2.5 or
less on DXA. No quantitative ultrasonography
cutoff existed at which sensitivity and specificity
were both high. [27]
Using the WHO cutoff value for the definition of
osteoporosis based on the t-score of ≤ –2.5 the
sensitivity and specificity of DXA were seen to
be 88.2% 62.5%. [28]
Also, QUS cannot be used for diagnostic
classification or staging of Osteoporosis, and it is
not clinically useful for monitoring the effects of
therapy. [29] Physiologically, calcaneal bone
tissue undergoes remodeling much more slowly
than central bone (spine and hip). Since bone
mineral content changes at different rates in
different sites of the body, QUS which evaluates
a single site will not be as accurate as a more
composite evaluation by DXA therefore early
osteoporotic changes may not be captured as
effectively by QUS as they would be by DXA
scan. [30] Analysis has shown, women diagnosed
by QUS are four times more likely to have a
fracture in the following year than women
screened with DEXA. [31]
3. CONCLUSION
Table 2 summarizes the relative advantages and
disadvantages of Calcaneal QUS versus Gold
standard DXA. For developing countries,
Calcaneal QUS can serve as a useful tool for
screening but does not have the value of
monitoring changes over time. Moreover,
different QUS machines have different cut off
parameters therefore cannot be compared either
with DXA or with each other over time. However
Calcaneal QUS, has the advantage of
convenience, mass use, low cost, avoiding
radiation and easy transport and portability. Its
results corroborate with DXA for predicting hip
fractures. Traditional WHO DXA cut offs should

Screening for Osteoporosis – Making an Informed Choice of DXA or Calcaneal QUS
ARC Journal of Orthopedics Page | 12
not be applied to Calcaneal QUS, and the same
should be based on individual device
recommendations. With these points in mind, a
QUS device maybe chosen for screening
Osteoporosis risk groups especially in
developing countries.
Table2. Comparative advantages and disadvantages of DXA and Calcaneal QUS
DXA
Calcaneal QUS
Most studied, gold standard and first line screening
method recommended by standard guidelines[30-32]
Suggested as alternative screening method if access
to DXA is limited
Done at multiple sites – like hip, and spine
Single site – Calcaneum (heel)
Standardized T score cut offs for low bone mass and
Osteoporosis
QUS T score cut offs usually greater than DXA cut
offs and are specific for the particular device. (DXA
cut offs cannot be applied to QUS)
Can be used for diagnosis and monitoring response to
therapy
Useful only for diagnosis
Can be used for diagnostic classification and disease
staging.
Should not be used for diagnostic classification and
disease staging.
Can pick up early disease
May not pick up early osteoporotic changes.
Difficult to transport device, requires skill in usage.
Not conducive for camps and high-volume onsite
screening
Convenient and easy to use and transport.
Suitable for camps and high-volume onsite
screening
High cost
Low cost
Exposure to ionizing radiation – not advised during
pregnancy
No exposure to ionizing radiation
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Citation: Varsha Narayanan, Screening for Osteoporosis – Making an Informed Choice of DXA or Calcaneal
QUS. ARC Journal of Orthopedics. 2019; 4(1):9-13. doi:dx.doi.org/ 10.20431/2456-0588.0401003.
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