The clinical significance of osteoporosis lies in the fractures that occur, and the
most important fracture is hip fracture. According to the 1994 World Health Organization
(WHO) criteria, the T-score is defined as: (BMDpatient–BMDyoung normal mean)/SDyoung
normal population, where BMD is bone mineral density and SD is the standard deviation.
When the femoral neck is measured in adult women, a cutpoint value of patient BMD
of 2.5 SD below the BMDyoung normal mean satisfies that the prevalence of osteoporosis
for those aged ≥50 years is about 16.2%, the same as the lifetime risk of hip fragility
fracture (FF) (1,2). If other sites are also considered, this cutpoint value identifies
approximately 30% of postmenopausal women as having osteoporosis, which is approximately
equivalent to the lifetime risk of FF at the spine, hip, or forearm. The FF prevalence
of older Chinese women is slightly less than half that of Caucasians (3,4). This is
the case for hip FF (5-7), radiographic vertebral FF (8), clinical vertebral FF (9-11),
and many other FF sites (3,4,12,13). As compared with Caucasians, Chinese demonstrate
an overall stronger skeleton property (14). For example, Walker et al. (15) reported
that postmenopausal Chinese women have a higher trabecular plate-to-rod ratio and
greater whole bone stiffness, translating into a greater trabecular mechanical competence.
Following the 1994 WHO definition, densitometric osteoporosis prevalence among a non-Caucasian
population should be in proportion to its relative osteoporotic fracture risk with
Caucasian data as reference (16). To achieve this goal, various region/ethnic-specific
reference BMD databases have been published (3). Furthermore, the cutpoint T-score
for defining densitometric osteoporosis should be adjusted according to the osteoporotic
fracture risk profile. Based on statistical modeling (3), we proposed that the femoral
neck cutpoint T-score is revised from ≤−2.5 to ≤−2.75 for Hong Kong older women when
a local BMD reference published by Lynn et al. (17) is applied. The same principle
can also be applied to Japanese older women if a local BMD reference published by
Iki et al. is used (3,18). In an empirical study on women with radiographic vertebral
FF as a surrogate clinical endpoint, we recently demonstrated that, at the mean age
of around 74, a femoral neck T-score of −2.60 for Italian Caucasians is equivalent
to −2.77 for Hong Kong Chinese, while a lumbar spine T-score of −2.44 for Italian
Caucasians is equivalent to −3.75 for Hong Kong Chinese (19). Moreover, our literature
analysis suggested that, while a cutpoint T-score ≤−2.5 for defining spine densitometric
osteoporosis is justified for Caucasian women, for East Asian women the same cutpoint
T-score much inflates the estimated prevalence of spine densitometric osteoporosis
(11).
To further support our argument that the cutpoint T-score for defining femoral neck
densitometric osteoporosis among East Asian populations should be lower than the conventional
value of ≤−2.5, we conducted an additional literature analysis. The hypothesis is
that, around the time when a proximal femur FF occurs (which is a clinical endpoint
for osteoporosis), East Asians measure a lower T-score than that of Caucasians. We
grouped together Chinese, Korean, and Japanese as East Asians. It has been suggested
that Korean and Japanese older women have similar FF risk profiles similar to those
of older Chinese women (5,13,20-23). On Dec 13th 2022, two structured literature searches
on https://pubmed.ncbi.nlm.nih.gov/ were conducted using the keywords combination
of ‘((hip OR femur OR femoral) AND fracture) AND T-score’, and ‘(BMD OR T-score) AND
hip fracture AND (Chinese OR Korean OR Japanese)’. These searches generated 1,558
results and 492 results respectively. The results were initially screened by their
titles, and then by their abstracts (when available). For potentially relevant items,
the full articles were retrieved for analysis. Though Singapore is a Southeast Asia
nation, data from Singapore were included as 75% of Singaporean populations are ethnically
Chinese.
We only included studies on proximal femoral fractures among older subjects while
excluded the studies included a significant portion of high energy trauma cases, thus
included cases are assumed to be mostly FF. Efforts were made that the reported cases
were only counted once in this analysis (note some authors might have used the same
case materials for different types of analysis and published more than one article).
We aimed to include studies concerning dual-energy X-ray absorptiometry areal BMD
measured around the time of fracture, and usually the fracture was shortly followed
by surgical intervention. Other excluding criteria were: (I) articles concerned with
patients group-wise systematically under a specific anti-osteoporotic treatment regime,
however, it was allowed when a portion of cases was under an anti-osteoporosis medication
as an usual care (as would be expected in a real-world clinic); (II) articles concerned
with specific types of patients such as those with diabetes mellitus type 2, however,
it was allowed for studies with a portion of their patients had a disease such as
diabetes mellitus type 2 (as would be expected among general community older subjects);
(III) articles only concerned with hip re-fracture patients; (IV) articles concerned
with atypical femur fracture; (V) articles concerned with femoral head subchondral
insufficiency fracture; (VI) articles concerned with ex vivo study; (VII) study cohorts
with fewer than 10 cases. For articles from East Asia, we only included studies which
used a local or an East Asian BMD reference. If this aspect was not specified in the
published article, the authors were contacted to validate this information, and articles
were excluded if this could not be validated (only one article was excluded due to
this reason). Finally, we included 12 articles (n=5 for East Asians and n=7 for Caucasians)
that reported women’s and men’s data separately, and 12 articles (n=7 for East Asians
and n=5 for Caucasians) that reported women’s and men’s data together. The articles
available for analysis were much fewer than initially anticipated. Many studies concerned
with proximal femur FF only reported BMD values instead of T-score values. Some studies
reported T-score classifications (such as 28% of the hip fracture patients had femoral
neck T-score of ≤−2.5) instead of the actual T-score values.
For the data in the articles included for analysis, the results are shown in
Figure 1
for female patients (24-33),
Figure 2
for male and female patients mixed (34-45), and
Figure 3
for male patients (24,28-30,32,33,46,47). For the data in
Figure 2
, females commonly constituted 2/3 of the cases, reflecting that hip fracture prevalence
among older women is about double of that among older men. A trend can be seen that
East Asian female patients measure a lower femoral neck and a lower total hip T-score
than those of Caucasians. The same trend is also tentatively noted for female patients’
lumbar spine T-score. For the data of male and female patients mixed, a trend is only
noted that East Asian patients measure lower femoral neck T-score. For male patients,
only a ‘possible’ trend is noted that East Asian patients measure lower total hip
T-scores. Another point noted is that, around the timepoint of a hip fracture, at
least for East Asians included in this study, male patients tend to measure higher
femoral neck and total hip T-scores than those of female patients (
Figure 4
) (24,28-30,32,33). Based on
Figure 4
, it appears that, a femoral neck T-score of −3.3 in East Asian women will be approximately
equivalent to a femoral neck T-score of −2.4 in East Asian men (a hip T-score of −3.0
in East Asian women will be approximately equivalent to a hip T-score of −2.4 in East
Asian men, note that femoral neck T-score and hip T-score are usually highly correlated).
This may suggest that different T-score cutpoints for classifying densitometric osteoporosis
should be applied for Asian men and women, on the other hand, this observation may
also be coincidental. Note, the 1994 WHO Study Group did not establish any guidelines
for the diagnosis of osteoporosis in men (1).
Figure 1
Distribution of T-scores of proximal femur fracture Caucasian female patients and
East Asian female patients. A trend is noted that East Asian female patients measure
lower FN, TH, and LS T-scores. (A) FN data, (B) TH data, (C) LS data. A1 and C1: Wilson
et al. (n=68 cases); A2 and C4: Olszewski et al. (n=37); A3 and C3: Schnabel et al.
(n=22); A4 and B1: Di Monaco et al. 2020 (n=350); A5, B2 and C2: Yeo et al. (n=91);
A6 and C6: Lee et al. (n=819); A7 , B5 and C7: Gani et al. (non-diabetic group n=350,
though the title of the article suggests only patients with severe osteoporotic hip
fracture, however, according to the methodology and the T-score values, they included
all low energy hip fracture patients); A8 and C5: Zhu et al. (n=24); B3: Ho et al.
(n=167); B4 and C8: Li HL et al. (n=268). FN, femoral neck; TH, total hip; LS, lumbar
spine.
Figure 2
Distribution of T-scores of proximal femur fracture Caucasian patients and East Asian
patients. Male and female patients were reported together. A trend is noted that East
Asian patients measure a lower FN T-score. (A) FN data, (B) TH data, (C) LS data.
A1 and C3: Heetveld et al. (n=111, 68.47% females); A2, B1, and C1: Amar et al. (n=314,
68.8% females); A3 and C2: Valentini et al. (non-diabetic group n=69, assumed a mean
age of 79.6 years old); A4 and B2: Ganhão et al. (n=214, 79.70% females); A5: Carlson
et al. (this is from the American Orthopaedic Association’s Own the Bone database.
93.3% were Caucasian and 78% were females. The mean age was 76.7 years. Hip, spine,
ankle/foot, wrist and shoulder counted for 51.6%, 11.2%, 7.9%, 6.7%, and 6.1% of the
fractures, respectively. Thus, this is not a pure hip fracture cohort); A6: Li XP
et al. (n=269, 69.50% females); A7 and B5: Xu et al. [n=360, 51.70% females, data
estimated from Fig. 5 of Xu et al. (34)]; A8 and B3: Hey et al. (n=106, 61.70% females);
A9: Kanno et al. (n=275, 80.00% females); A10: Kang et al. [n=159, 69.8% females.
Whether the T-score was computed using an Asian bone mineral density reference was
not confirmed by us (but likely an Asian bone mineral density was used considering
other publications from the same institution). Even if a Caucasian bone mineral density
reference was used to compute the T-score and then T-score is adjusted according to
the results of Lo et al. (35), the datapoint of Kang et al. (36) will still be closer
to the Asian data cluster than to the Caucasian data cluster]; B6 and C5: Yamamoto
et al. (n=390, 78.4% females); B4 and C4: Cha et al. (n=59, 72.80% females). Arrow
for A7 and B5 datapoints (Xu et al.): most of the other data entries had approximately
2/3 of the cases being females, however for A7 and B5 approximately only 1/2 were
females. As males tend to measure higher FN and TH T-scores than females, if A7/B5
had 2/3 cases being females, then the value for A7/B5 would have been measured even
lower. Xu et al. only included those aged between 80–90 years (mean age: 84.2 years
which is not very different from other studies). FN, femoral neck; TH, total hip;
LS, lumbar spine.
Figure 3
Distribution of T-scores of proximal femur fracture Caucasian male patients and East
Asian male patients. A ‘possible’ trend is noted that East Asian patients measure
a lower TH T- score (however, the data certainly is not conclusive). (A) FN data,
(B) TH data, (C) LS data. A1 and C1: Wilson et al. (n=11); A2, B1, and C3: Cesme et
al. (n=20); A3 and B3: Di Monaco et al. 2018 (n=80); A4, B2 and C2: Yeo et al. (n=21);
A5 and C5: Lee et al. (n=271); A6, B5, and C4: Gani et al. (n=162, non-diabetic group);
B4: Ho et al. (n=72); B6 and C6 Li HL et al. (n=92). Note studies on Caucasian males
mostly had limited sample size. FN, femoral neck; TH, total hip; LS, lumbar spine.
Figure 4
In total six studies reported both males’ data and females’ data (24,28-30,32,33),
data from all four East Asian cohorts show FN and TH T-scores of proximal femur fracture
male patients measure higher than those of female patients. A trend for data of Caucasians
can not be ascertained. Each line represents data from the same report. TH, total
hip; FN, femoral neck.
There are many limitations to the current analysis. The patient populations included
in the current analysis were highly heterogeneous, while the number of studies available
for analysis is small. In theory, for the studies which reported the BMD values and
the specific type of bone densitometer used, we could use a suitable ethnic specific
BMD reference database and perform an adjustment to count for the bone densitometers
employed to derive T-scores. However, we did not choose to do this as we consider
our analysis as a ‘test-of-the-concept’ study. Since the expected trend was already
shown, we did not want to further complicate our analysis, thus we chose only to use
the T-score results as they were reported by the authors. The trend that older East
Asian patients tend to measure lower femoral neck and total hip T-scores than older
Caucasians as shown in the current analysis was not strong nor a ‘clear-cut’. This
is probably not surprising. Our proposed cutpoint T-score for female femoral neck
only differs by −0.2 to −0.25 from the conventional value of −2.5 (3). However, its
impact on epidemiological studies will not be trivial. As an example, using the Japanese
data of Iki et al., an adjustment of femoral neck T-score from ≤−2.5 to ≤−2.75 can
lower osteoporosis prevalence for older Japanese women aged 50–79 years from 12% to
7.5% (3). Another point is that the precision of BMD measures is affected by many
factors. Many reports specified that femoral neck and total hip BMD were measured
using the contra-lateral non-fractured hip, while a few articles did not report such
details. We can only assume the necessary steps to ensure a satisfactory level of
measurement precision were taken by the authors. Note the right and left hips commonly
have very similar BMD values. For the current analysis, we initially anticipated a
bigger difference for lumbar spine T-score between East Asians and Caucasians. The
data in
Figures 1-3
for lumbar spine T-score may reflect that lumbar spine T-score is not as predictive
for hip fracture risk as femoral neck or total hip T-scores. The measurement of lumbar
spine BMD is complicated by spine degeneration which can lead to artificially higher
BMD measures, thus only a lower lumbar spine T-score is relevant rather than the mean
lumbar spine T-score. In this study, except for the data of Carlson et al. (41), all
other Caucasian data are from Europe and Near East. The ethnicities of the patients
in their studies were mostly not specified, we take it that it is a reasonable assumption
that most of their older patients were Caucasians.
In conclusion, our literature analysis suggests that, around the time of a hip fracture,
older East Asian female patients tend to measure lower femoral neck and total hip
T-scores than older Caucasian female patients.
Supplementary
The article’s supplementary files as
10.21037/qims-23-65