British Journal of Radiology (2004) 77, 740-744
© 2004 British Institute of Radiology
doi: 10.1259/bjr/28072039
Normative data for ultrasound measurement of the calcaneus within different female ethnic groups
H J Hinkley, PhD
I P Drysdale, PhD, DO
N J Walters, PhD
and
D Bird, BSc
British College of Osteopathic Medicine, 6 Netherhall Gardens, London NW3 5RR, UK
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Abstract
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The purpose of this study was to generate normative broadband ultrasound attenuation data for UK resident Indian-Asian, African-Caribbean and Chinese women, aged 20–80 years, using the McCue Cubaclinical II device. Additionally, comparisons were made against available Caucasian data previously collected by the authors. Exclusions were: use of hormone replacement therapy, corticosteroids or thyroxine for more than 6 months; menopause before the age of 45 years; oophrectomy; lactation within the preceding year; rheumatoid arthritis or a previous osteoporotic fracture. 977 women were recruited from various community centres, from a local GP surgery and from university colleges in the London area. Broadband ultrasound attenuation and velocity of sound were determined for the left and right os calces. Repeat measures on each side after re-positioning, to allow for anatomical variation, were averaged. Significance was set at a minimum level of 0.05. There were significant differences in non-dominant and dominant measures in all ethnic groups except African-Caribbean. For comparison purposes the means of the non-dominant measurements were plotted against age using a polynomial model to give the best data fit. No significant difference was found between non-dominant broadband ultrasound attenuation measurements for either Asian or Chinese when compared with the Caucasian sample populations. A significant difference in broadband ultrasound attenuation was found between African-Caribbean and Caucasian, with African-Caribbean between 10% (age group 20–30 years) and 29% (age group 70–80 years) higher. There was no significant difference in body mass index between Caucasian and Chinese groups, but significant differences were found between Caucasian and Asian, and between Caucasian and African-Caribbean groups.
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Introduction
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Broadband ultrasound attenuation (BUA) has been shown to be of predictive value in the assessment of osteoporotic fracture by both retrospective [1–3] and prospective studies [4–8]. Normative data for the Caucasian population has already been issued by the suppliers of the various machines utilizing ultrasound bone densitometry. With particular reference to the McCue Cubaclinical II system (which assesses the calcaneus) no such data exist for ethnic populations other than Caucasian. Thus all scans currently have to be compared with Caucasian data. This could create a potential error as it has been established that there are differences in bone mineral density (BMD) in different ethnic groups [9]. Previous studies using different technologies have found ethnic variations of bone composition. A large study (NHANES III) of USA men and women using dual energy X-ray absorptiometry (DXA) of the hip showed both regional and ethnic differences across the USA [10], and a further study (NORA program) of ethnic groups using single energy X-ray absorptiometry (SXA) of the heel also showed differences [11]. The ultrasound wave is modified by both the BMD and by the microarchitectural structure of cancellous bone. This sensitivity to the combination of bone tissue characteristics is not found using DXA or SXA.
The aim of this study was to provide normative data using the McCue Cubaclinical II system for UK resident Indian-Asian, African-Caribbean and Chinese women aged 20–80 years, and to make comparisons with unpublished Caucasian data previously collected by the authors.
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Methods
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Female volunteers from Indian-Asian, African-Caribbean and Chinese populations, from community centres, university colleges and a GP surgery in the London area were used as an opportunistic sample. Informed consent was obtained using a format approved by the college Ethics Committee, with subject's anonymity maintained throughout. The community centres and GP surgery were sources of all ages, with the colleges providing mainly 20–29 year olds. A questionnaire was completed on interview, using interpreters if necessary, to determine eligibility for the study and background information, including handedness and diet. In the case of diet, subjects were asked to identify whether they had a westernised, traditional or mixed diet. The questionnaire enabled the following exclusion criteria to be applied: use of hormone replacement therapy, corticosteroids or thyroxine for more than 6 months; menopause before the age of 45 years; oophrectomy; lactation within the preceding year; rheumatoid arthritis; a previous osteoporotic fracture. Weight and height were measured at the time of ultrasound scanning.
Three trained operators used the McCue Cubaclinical II system to provide measurements of BUA and velocity of sound (VOS) for the left and right os calces. The measurement coefficient of variation of the three operators for BUA was 4%. The Cubaclinical incorporates a system of repeat measurements until 7 readings are within 5 dB MHz–1 from which an average is produced. The foot was measured three times in succession with the heel being re-positioned between each measurement to compensate for any minor anatomical variation and possible change in ultrasound coupling. The mean was then taken. Results were compared with a set of Caucasian women who satisfied the inclusion criteria and had been previously scanned at the British College of Osteopathic Medicine. For this group the mean was based on two or three measurements due to changes in clinic protocol over time. Each ethnic group was divided into age decades and compared using the Student's t-test.
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Results
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A total number of 977 women were assessed (Table 1
) to provide normative data for four ethnic groups. Background information can be found in Table 2. A t-test showed no significant difference in body mass index (BMI) between all subjects in the Caucasian and Chinese groups but significant differences occurred between Caucasian and Asian/African-Caribbean groups, except for the Asian age range 70–80 years (Table 3).
A t-test was applied to the non-dominant versus dominant measures (Table 4). "Dominant" was defined as the foot with which one would kick a ball. There was a significant difference between non-dominant and dominant in each ethnic group except African-Caribbean. These differences were not always evident in individual age ranges. However, where an age range consists of a larger number of subjects, the overall data are skewed in favour of the larger group. Bilateral differences have previously been reported by the authors [12, 13].
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Table 4. Differences in non-dominant and dominant broadband ultrasound attenuation measurements: Student's t-test
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For graphical presentation of normative data, age was plotted against the non-dominant BUA and VOS. A polynomial model gave a slightly better fit in each case (Table 5). Figure 1 shows the linear regression lines for each ethnic group in comparison with the McCue Caucasian normative line. Non-dominant measurements and linear plots were chosen to be consistent with the published McCue data.
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Table 5. Regression analysis of broadband ultrasound attenuation (BUA)/velocity of sound (VOS) against age – R2 – using linear and polynomial models
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Figure 1. Normative data. Linear regressions for mean non-dominant broadband ultrasound attenuation (BUA).
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Student's t-tests were applied to compare non-dominant BUA measurements for each ethnic group with Caucasian data (Table 6). A significant difference was found between Caucasian and African-Caribbean populations at each decade with African-Caribbean between 10% (age group 20–30 years) and 29% (age group 70–80 years) higher (Table 7).
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Table 6. Differences in non-dominant broadband ultrasound attenuation measurements between Caucasian and other ethnic groups: Student's t-test
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Table 7. Mean non-dominant broadband ultrasound attenuation and confidence interval (95% CI) for each ethnic group
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Discussion
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This study has generated normative data for different UK resident ethnic groups, enabling subsequent scans to be more appropriate. As found by other studies [14] a significant difference was found between African-Caribbean and Caucasian groups. The NORA program using SXA of the heel also showed African-American women to have the highest BMD and Asian the lowest [11].
Agreement to participate in the study was found to be greater at the community centres where workers could more easily organize the group. The membership of these centres tended to be amongst the older age groups, particularly in the case of the African-Caribbean and Chinese groups, making it difficult to access the younger age subjects. It was observed that the younger groups also had less interest in bone density scanning, since it was often perceived as an older person's problem. There was a perceived general lack of understanding of osteoporosis and health in general, particularly in the Indian-Asian community. A report by the National Osteoporosis Society in England in 1995 [15] explored the health education needs of South Asian communities in relation to osteoporosis and highlighted the general lack of knowledge in this area with language problems being a major barrier. Subjects were volunteers and therefore not a true random sample.
In all groups the polynomial regression line for BUA data illustrates a small decline between age groups 20 to 59 years followed by a sharper fall up to the age of 80 years. Comparisons can be made between this study and the findings of Langton [16] who also produced normative Caucasian data using the Cubaclinical system. Langton showed that the polynomial model gave a better fit when compared with the linear, and the spread of data and R2 values in the present study were very similar to those found by Langton.
The Indian-Asian and Chinese normative BUA data are not significantly different from that of the Caucasian population, but BUA of the African-Caribbean group is significantly higher than the Caucasian. These findings are in line with published data, which show that bone mass is greatest and fracture rate is lowest in those of African heritage [14]. It therefore seems logical that when measuring African-Caribbean women, the results should be interpreted against an appropriate normative data line.
A detailed analysis of diet and exercise factors, particularly in those subjects who have changed their lifestyle since residing in the UK, is the subject of future work. It can be seen (Figure 1
) that in the case of the younger Chinese and Asian subjects, BUA values were marginally lower than Caucasian, although not statistically significant, whereas the older groups were slightly, but not significantly, higher. It is possible that the older groups performed more exercise when younger, for example an active young life followed by a more sedentary lifestyle once in the UK, although a number of the women scanned were attending gentle exercise classes run by the community centres.
When interpreting the graphs showing reduction of BUA with age, consideration should be given to the probability that a current 60–80-year-old is likely to have experienced a different and possibly healthier lifestyle in younger years, when they were building bone, compared with a current 20-year-old. The graphs for each ethnic group may therefore present an optimistic view, since a current 20-year-old may be expected to reach a lower bone density than that inferred by the graphs of age 80 years. This could result from starting from a lower initial baseline. Studies indicate that modern young persons' lifestyles are more likely to result in lower accrual of bone mass when compared with lifestyles of current 80 year olds when they were young [17–23].
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Acknowledgments
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Appreciation to the many people who supported this study by donating their time and to the participating community centre leaders, who assisted in organizing volunteers for the study. Thanks also to Melanie Shale who assisted with the Cubaclinical scanning.
Received for publication April 28, 2002.
Revision received March 18, 2004.
Accepted for publication April 6, 2004.
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Abstract
Introduction
