Introduction
Osteoporosis is one of the most common diseases of aging, with an increasing prevalence of disease and fractures with age [
1]. The worldwide prevalence of osteoporosis is difficult to ascertain due to differing definitions and diagnostic criteria. However, one-in-four women and one-in-eight men aged 50 years or older have osteoporosis [
2]. If these proportions are extrapolated to the current world population statistics [
3], over 228 million adults aged 55 years or older would have osteoporosis, which is a marked increase from the previous estimate of 200 million in 2006 [
4].
Characterized by a gradual loss in areal bone mineral density (aBMD) and deterioration of bone microarchitecture, clinically osteoporosis leads to increased bone fragility and subsequent fragility fractures—typically of the forearm, humerus, vertebra, and hip (femur and femoral neck). Osteoporotic fractures, in particular hip fractures, have an important and serious health impact leading to significant increases in mortality, pain, and loss of independence [
5,
6]. Importantly, osteoporosis is a silent disease as patients are often unaware of the disease progression due to a lack of observable symptoms until a fall or an impact of an adequate force results in a bone fracture. Therefore, identifying individuals with increased risk of experiencing a fracture is crucial for early intervention and minimization of fracture risk. This applies to all fractures, regardless of the level of aBMD [
7]. However, despite acknowledging the negative consequences of fractures, such as reductions in quality of life and higher mortality associated with fracture [
5,
6] and the efficacy of treatment to reduce risk, osteoporosis remains widely under-diagnosed and under-treated [
8‐
11].
Thus, while there are several country-specific guidelines to identify those patients at increased risk of fractures, there is great diversity in the case-finding strategies globally, particularly between eastern and western countries [
12,
13]. To address these differences, this narrative review by members of the East-meets-West working group within the European Calcified Tissue Society (ECTS) aims to summarize the case-finding strategies in osteoporosis, with a focus on a comparative review between a selection of Asian and European countries—including China, Japan, South Korea, the UK, and German-speaking countries (Germany, Austria, a Swiss-speaking Switzerland).
Introduction to case-finding
Osteoporosis is most commonly classified using the World Health Organization (WHO) operational definition and based on aBMD measurement using dual X-ray absorptiometry (DXA), relative to the aBMD of an average young adult [
14‐
16]. Using this approach, osteoporosis patients are those with an aBMD in the femoral neck (hip), spine, or forearm that is 2.5 standard deviations or more below that of the mean of healthy young adult females (the so-called T-score) [
14]. Fracture risk decreases exponentially with increasing aBMD, and low aBMD is a strong predictor of fracture of multiple types, even over more extended periods [
17]. However, it is well established that fractures can occur in patients without an aBMD T-score of − 2.5 and below. Indeed, since there are many more subjects with an aBMD T-scores above − 2.5 than with an aBMD T-score below − 2.5, most fractures occur in people with BMD T-score > − 2.5 [
18]. Consequently, clinical factors such as age, sex, family history, smoking status, and physical activity, along with disorders or medications with a negative impact on bone, likely play important roles in fracture risk and should be included in the case-finding assessment.
Indeed, using aBMD alone to identify patients at risk for a fracture will likely have poor sensitivity as many patients at risk for a fracture will not be identified and thereby not offered therapeutic management. Technically, aBMD as a projection measure is affected by body size, but definitions based on volumetric BMD, assessed by quantitative computed tomography (QCT), also show limited sensitivity. More importantly, there are a number of disorders other than osteoporosis, where aBMD is also substantially reduced (e.g., multiple myeloma or osteogenesis imperfecta), thereby pointing out the need for differential diagnosis. DXA-based aBMD assessment is, therefore, an indicator of bone mass-related fracture risk as opposed to fracture risk resulting from extra-skeletal factors, such as a propensity for falling or due to deteriorated bone material properties. This reflects a strength (low aBMD indicates the need to target treatment to the bone) and a weakness (limited capability to identify risks due to causes other than bone mass deficits) of using DXA alone to identify osteoporosis. Thus, low aBMD should be considered a risk factor for fracture rather than a singular definition of osteoporosis. Accordingly, considering aBMD, in addition to other clinical risk factors, will increase fracture risk assessment accuracy.
Several clinical tools have been developed to calculate an individual’s risk of fracture in light of this. The most widely used tool is the fracture risk assessment tool FRAX® (
www.shef.ac.uk/FRAX). Developed at the University of Sheffield in the UK, FRAX® estimates the 10-year probability of major osteoporotic (hip, forearm, proximal humerus, and clinical vertebral) and hip fracture. The FRAX® algorithm determines the fracture probability by integrating the weight of important clinical risk factors, with or without an aBMD measurement. In the UK, the SCreening for Osteoporosis in Older women for the Prevention of fracture [SCOOP] study tested whether risk-based screening using FRAX® effectively reduced fracture incidence [
19,
20]. The study was a community-based screening intervention of 12,483 women aged 70 to 85 years in the UK. In the screening arm, licensed osteoporosis treatments were recommended in women identified to be at high risk of hip fracture using the FRAX® risk assessment tool (including aBMD measurement). In the control arm, standard care was provided. Screening led to a significant 28% (adjusted hazard ratio [aHR] 0.72, 95% confidence interval [CI] 0.59–0.89) reduction in hip fractures over 5 years, with no overall reduction in fracture risk [
19].
Another study testing whether a FRAX®-based risk assessment effectively reduced fracture incidence in the Danish Risk-stratified Osteoporosis Strategy Evaluation (ROSE) study [
21,
22]. Here, patients were randomized before the invitation to screening was sent out. Participants filled out a questionnaire to calculate the FRAX® 10-year risk of major osteoporotic fracture. Researchers did not inform women in the control group about the result of the FRAX calculation. In contrast, women in the intervention group, with a ≥ 15% risk, were invited to undergo DXA scanning. The woman and her general practitioner (GP) received the examination results by letter. The information included treatment recommendations based on the Danish national guidelines; however, the patient and GP made the treatment decisions. The primary intention-to-treat analysis of the 34,229 women aged 65–80 years showed no significant overall effect on major osteoporotic fracture (aHR 0.99, 95% CI 0.92–1.06) or hip fracture (aHR 1.00, 95% CI 0.89–1.13) between those randomized to the screening group compared to the control group. However, a pre-planned per-protocol analysis, among only those who returned the questionnaire with sufficient information to calculate FRAX®, showed a slight risk reduction in the screening group compared to women in the control group for major osteoporotic fracture (aHR 0.91, 95% CI 0.83–1.01) and hip fracture (aHR 0.82, 95% CI 0.67–1.01). However, compared to controls with a FRAX® ≥ 15%, the screening group showed a significant reduction in major osteoporotic fractures (aHR 0.87, 95% CI 0.77–0.99) and hip fractures (aHR 0.74, 95% CI 0.58–0.95) was observed [
21]. However, we note that a self-selection bias may be present in the per-protocol analyses.
While the SCOOP study and the per-protocol analyses in the ROSE study support the notion that screening for fracture risk is associated with a significant risk reduction for hip fractures, the SALT Osteoporosis Study (SOS) from the Netherlands failed to find a similar conclusion [
23]. This study included only women aged 65 to 90 years, with more than one clinical risk factor for fracture. Women with a high 10-year FRAX® risk, or a prior vertebral fracture, were offered osteoporosis treatment. Among the 5575 patients in the screening group, 25% (
n = 1417) indicated to receive osteoporosis treatment, yet during follow-up, there was a non-significant effect on fracture risk, including hip fracture (aHR 0.91, 95% CI 0.1–1.15) [
23]. However, unlike the SCOOP or ROSE studies, the definition of the high-risk group is unclear, and there are important caveats that may underestimate the effect of screening programs [
24].
Since 2008 when the FRAX® tool was launched, it has been diversified for use in 63 countries, currently 35 European countries and 11 countries/regions in Eastern Asia, with each tool calibrated based on estimates of the national hip fracture and mortality epidemiology. Currently, calibrated FRAX® models are available for 58 countries globally [
25]. A comprehsive overview of these can be identified in systematic reviews by the National Osteoporosis Guideline Group and the International Osteoporosis Foundation (IOF) [
25]. Importantly, as it was primarily developed in Caucasian populations [
25,
26], FRAX® may overestimate the fracture risk in minority populations (including Asian, African, and Hispanic populations) [
27]. Thus, local calibration is pertinent. A discussion of the strengths and limitations of FRAX® is available elsewhere [
27]. For example, in contrast to hip fractures, data on the incidence of other fractures is limited. Thus, to construct a FRAX® tool in the absence of such data, it is assumed that the ratio of hip fractures to other types of fractures is similar across populations. While true in Caucasians, this needs to be confirmed in other ethnicities. For example, in elderly (> 65 years) Hong Kong Chinese and Japanese individuals, the ratio of vertebral fractures to hip fractures may be higher [
28].
Currently, FRAX® is widely used, particularly in China, Hong Kong, Japan, South Korea, and Taiwan, where there are population-specific FRAX® algorithms. Limited access to DXA in some countries remains an issue, with some adopting the use of quantitative ultrasound (QUS) measurements. To date, FRAX® does not accommodate the QUS [
29,
30]. Additionally, other screening tools developed to calculate the likelihood of underlying osteoporosis rather than fracture risk are available. Examples include the Osteoporosis Self-Assessment Tool for Asians (OSTA) or the IOF 1-min questionnaire, which simply detects the presence of risk factors associated with osteoporosis. Such tools have been implemented in China to identify those at risk for osteoporosis, thereby optimizing DXA scan use given limited resources [
31].
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