Screening for osteoporosis: what is the role of heel ultrasound?

Potential roles for quantitative ultrasound in the management of osteoporosis

OBJECTIVE

To assess the validity of four models for the role of quantitative ultrasound (QUS) in the management of osteoporosis.

DESIGN

Cross-sectional survey and review of literature.

SETTINGS

Nuclear medicine departments of three teaching hospitals in Sydney.

SUBJECTS

1000 women aged 22 to 88 years (mean, 59 years) referred for assessment of osteoporotic fracture risk.

MAIN OUTCOME MEASURES

BMD categories as defined by dual-energy x-ray absorptiometry (DEXA) of the lumbar spine and proximal femur, and QUS category as defined by calcaneal ultrasound stiffness; prevalence of DEXA-defined osteoporosis in the different QUS categories.

RESULTS

In women with QUS Achilles stiffness < or = 70 the prevalence of axial osteoporosis was 51%, whereas in the group with stiffness > 70 the prevalence of axial osteoporosis was 8%. In women 65 years and over the corresponding values were 59% and 17%.

CONCLUSIONS

Of the four possible models for QUS, the use of QUS for the estimation of BMD, or in a "standalone" model, can not be recommended at the current time. The model of QUS as a "prescreening" modality may be acceptable assuming adequate education of clinicians and patients of its limitations, particularly the risk of false negatives. The model of QUS as one factor in a composite risk factor assessment of patients is promising but more data are required.

Principles of screening

Preventive medicine is an increasingly important area of clinical practice. Conceptually, preventive medicine involves three tasks of the clinician: screening, counseling, and immunization/prophylaxis. This opening article reviews some of the basic tenets underlying screening including basic epidemiologic principles, characteristics of a good screening situation, barriers to screening, and some of the potential hazards of screening.

An evaluation of a new gel-coupled ultrasound device for the quantitative assessment of bone

Quantitative ultrasound (QUS) is now being accepted as a tool in the assessment of bone status. Most QUS devices measure broadband ultrasound attenuation (BUA) and speed of sound (SOS). A newly introduced device, the Acoustic Osteo-Screener (AOS-100), measures both SOS and an attenuation related parameter called the transmission index (TI) and provides a derived parameter called osteo sono-assessment index (OSI). The purpose of this study was to examine the reproducibility of this new device, compare the results with the UBA 575+ and evaluate the effect of using two platforms to compensate for different foot sizes on the measured values. 83 subjects aged 21-89 years, who gave informed consent, were recruited. Subjects were assigned to three different groups determined by age and health status. The short-term measurement precision (expressed as root mean square coefficient of variation) of SOS (0.13-0.16%) and TI (1.18-1.96%) was similar to and better than that obtained for the UBA 575+. Significant negative correlations were found between the differences in SOS measured with the two platforms (adaptors to adjust the position of the foot relative to the foot plate) and foot length (p < 0.0001). This implies that small feet are more influenced by the differences of measured location. All QUS parameters measured with the small platform were found to be significantly smaller than those with the large platform (p < 0.0001). The mean percentage differences were 0.6% in SOS, 2.8% in TI and 4.3% in OSI with the large foot platform giving larger value results. Proper use of the platforms resulted in more reproducible SOS and TI. This study demonstrated that the newly developed AOS-100 parameters TI and OSI were highly reproducible. This study also demonstrated that the use of an inappropriate platform can cause discrepancies in QUS readings and poor reproducibility.

The effectiveness of bone density measurement and associated treatments for prevention of fractures. An international collaborative review

This review assesses the evidence regarding the effectiveness of bone density measurement (BDM) screening and related interventions--hormone replacement therapy (HRT) and intranasal salmon calcitonin (SCT[N])--in menopausal women to prevent fractures in later life. Data sources included systematic reviews of evidence and relevant primary studies identified through literature searches on MEDLINE and EMBASE. Study selection included trials of BDM screening programs, prospective studies examining the predictive value of BDM, randomized controlled trials, cohort studies, and case-control studies of HRT and SCT (N). The evidence was evaluated using a classification system incorporating study design and quality. Outcomes were measured in terms of relative risk of fracture for a 1 SD decrease in bone mineral density below the age-adjusted mean, relative risks or odds ratios for fractures associated with treatments, and proportion of hip fractures potentially prevented by BDM screening linked to treatments. Fair evidence from prospective cohort studies suggests that BDM can predict the risk of fractures, but not with high accuracy. Fair evidence from low-quality randomized controlled trials and observational studies suggests that HRT and SCT(N) are efficacious in preventing fractures. Good evidence supports the efficacy of these treatments in preserving bone mass, but there is fair evidence that the effect wears off after cessation of therapy. There is little evidence on the impact of screening menopausal women with BDM in association with HRT or SCT(N) treatment. Estimates based on combining existing evidence regarding the predictive value of BDM and efficacy of HRT suggests that 1-7% of hip fractures might be prevented.

The characterization of broadband ultrasound attenuation and fractal analysis by biomechanical properties

The purpose of this study was to show how the difference in structure affects the mechanical properties of bone and if BUA or fractal analysis is able to detect these changes in mechanical properties. A total of 38 cancellous bone cubes were obtained from seven bovine tibiae (32 specimens) and one human tibia (6 specimens). BUA was measured in the superior/inferior (SI), medial/lateral (ML), and anterior/posterior (AP) directions for each specimen. The fractal dimension was estimated by using the continuous alternating sequential filter (CASF) pyramid approach to handle fractal dimension estimation of small images. Nondestructive compressive tests were also performed in the three orthogonal directions for each sample. The correlations between BUA and density were statistically significant for all three directions. The correlation between BUA and elastic modulus varied depending on the direction in which the two parameters were measured. The best correlation was in the AP directions (r = 0.75, p < 0.0001), followed by the ML direction (r = 0.52, p = 0.0006), and finally the SI direction (r = 0.18, p = 0.28). The only significant correlation between fractal dimension and density was in the SI direction (r = 0.39, p = 0.015). There was significant correlation between fractal dimension and elastic modulus in all three directions, but the direction that exhibited the best correlation was the SI direction (r = 0.61, p < 0.0001). The correlation coefficients for the AP and ML directions were 0.45 (p = 0.0046) and 0.34 (p = 0.0377), respectively. A multivariate model, carried out to predict the elastic modulus from the BUA or fractal dimension including density, demonstrated that the correlation coefficient significantly increased in all three directions for BUA and fractal dimension. After adjustment for density, significant relationships between elastic modulus and BUA or fractal dimension were still found (p < 0.05).

Influence of handedness on calcaneal ultrasound: implications for assessment of osteoporosis and study design

Calcaneal ultrasound has been increasingly studied for its potential in the assessment of osteoporotic fracture risk. The accuracy of such an assessment is, in part, dependent on the reproducibility of the measurement. This study examines the impact of handedness on ultrasound measurements [broadband ultrasound attenuation (BUA) and velocity of sound (VOS)] in the calcaneus. Two hundred and sixty-four subjects (57 men and 297 women) aged 51.1 +/- 13.6 years (mean +/- SD) were studied. For each subject, calcaneal ultrasound measurements were performed on both heels with a McCue CUBA ultrasound densitometer. Right-handed dominance (94.7%) was determined by structured interview. In men, BUA measurements were significantly higher on the dominant side: mean difference 4.1 +/- 1.5 dB/MHz (mean +/- SD; p = 0.009), equivalent to 4.2 +/- 1.5% and more than 4 times the average rate of annual change in BUA. The difference between sides was greater in young (< 50 years) than old men (> 50 years). Among the women, the difference was not statistically significant (0.7 +/- 0.9 dB/MHz; p = 0.4); however, it was significant in younger women (20-30 years) (99 +/- 4 vs 90 +/- 4 dB/MHz, p = 0.01). By contrast VOS did not differ between sides in either men or women irrespective of age. Within-subject standard deviation of BUA was 9.8 dB/MHz for men and 8.6 dB/ MHz for women and the component due to right and left difference was 8.4 dB/MHz for men and 6.9 dB/MHz for women. This variability of BUA between right and left heels could increase the false-positive rate by up to 28% for a cut-off of 2 SD below the mean. These data indicate that variation between left and right heel measurements of BUA is higher than that of random error measurements, particularly in men and younger, presumably more physically active subjects. Although VOS measurements were not side dependent, in the smaller number of studies examining VOS and fracture risk, VOS appears to have a weaker predictive power than BUA. Clinical and epidemiological studies involving calcaneal BUA measurements should standardize the side measured to either the dominant or non-dominant heel, to reduce within-subject variation and increase their power.