Reproducibility of volume-adjusted bone mineral density of spine and hip from dual X-ray absorptiometry

Generation of a 3D proximal femur shape from a single projection 2D radiographic image

Generalized Procrustes analysis and thin plate splines were employed to create an average 3D shape template of the proximal femur that was warped to the size and shape of a single 2D radiographic image of a subject. Mean absolute depth errors are comparable with previous approaches utilising multiple 2D input projections.

INTRODUCTION

Several approaches have been adopted to derive volumetric density (g cm(-3)) from a conventional 2D representation of areal bone mineral density (BMD, g cm(-2)). Such approaches have generally aimed at deriving an average depth across the areal projection rather than creating a formal 3D shape of the bone.

METHODS

Generalized Procrustes analysis and thin plate splines were employed to create an average 3D shape template of the proximal femur that was subsequently warped to suit the size and shape of a single 2D radiographic image of a subject. CT scans of excised human femora, 18 and 24 scanned at pixel resolutions of 1.08 mm and 0.674 mm, respectively, were equally split into training (created 3D shape template) and test cohorts.

RESULTS

The mean absolute depth errors of 3.4 mm and 1.73 mm, respectively, for the two CT pixel sizes are comparable with previous approaches based upon multiple 2D input projections.

CONCLUSIONS

This technique has the potential to derive volumetric density from BMD and to facilitate 3D finite element analysis for prediction of the mechanical integrity of the proximal femur. It may further be applied to other anatomical bone sites such as the distal radius and lumbar spine.

Effect of total hip bone area on osteoporosis diagnosis and fractures

DXA is affected by skeletal size, with smaller bones giving lower areal BMD despite equal material density. Whether this size effect confounds the use of BMD as a diagnostic and fracture risk assessment tool is unclear. We identified 16,205 women of white ethnicity >or=50 yr of age undergoing baseline hip assessment with DXA (1998-2002) from a population-based database that contains all clinical DXA test results for the Province of Manitoba, Canada. Total hip measurements were categorized according to quartile in total hip bone area (Q1 = smallest, Q4 = largest). Longitudinal health service records were assessed for the presence of nontraumatic osteoporotic fracture codes during a mean of 3.2 yr of follow-up after BMD testing (757 osteoporotic fractures, 186 hip fractures). Total hip bone area strongly affected osteoporosis diagnosis with much higher rates in Q1 (14.4%) than Q4 (8.9%). However, incident fracture rates were constant across all area quartiles, and prevalent fractures were paradoxically fewer in smaller area quartiles (p < 0.001 for trend). Age was a potential confounder that correlated positively with area (r = 0.12, p < 0.0001). When age was not included in a Cox regression model, Q1 seemed to have a lower rate of incident osteoporotic fractures (HR = 0.80, 95% CI = 0.66-0.98, reference Q4) and hip fractures (HR = 0.63, 95% CI = 0.43-0.94) for a given level of BMD. In age-adjusted regression models, total hip BMD was strongly predictive of incident osteoporotic fractures (HR per SD = 1.83, 95% CI = 1.68-1.99) and hip fractures (HR per SD = 2.80, 95% CI = 2.33-3.35), but there was no independent effect of bone area (categorical or continuous). Nested matched subgroup analysis and ROC analysis confirmed that bone area had no appreciable effect on incident fractures. We conclude that total hip areal BMD categorizes a substantially higher fraction of women with smaller bone area as being osteoporotic despite younger age. Incident fracture rates correlate equally well with BMD across all bone area quartiles when adjusted for age.

Race/ethnicity and fracture risk assessment: an issue that is more than skin deep

The study of race/ethnicity in relation to health outcomes and health disparities is of great importance in medicine. This is as true in the field of osteoporosis as it is in others, and it comes into sharp focus when the question of population-specific reference data for bone densitometry arises. Race/ethnicity can be viewed as both an ecosocial construct and as a biomedical concept. Whether or not, and how, to use race/ethnicity in fracture assessment potentially places these two paradigms in opposition. In this article, some of the issues that need to be considered to develop a rational approach to reference data selection and a globally acceptable measure of fracture risk are reviewed. Race/ethnicity is often a proxy for other disease-related risk factors. Understanding fundamental risk factors goes beyond the language of race/ethnicity.

Cross-calibration and minimum precision standards for dual-energy X-ray absorptiometry: the 2005 ISCD Official Positions

The International Society for Clinical Densitometry (ISCD) Committee on Standards of Bone Measurement (CSBM) consists of experts in technical aspects of bone densitometry. The CSBM recently reviewed the scientific literature on cross-calibration and precision assessment. A report with recommendations was presented at the 2005 ISCD Position Development Conference (PDC). Based on a thorough review of the data by the ISCD Expert Panel during the conference, the ISCD adopted Official Positions with respect to (1) cross-calibration when changing or replacing hardware; (2) the approach to cross-calibration when an entire system is changed to one made by either the same or a different manufacturer; (3) when no cross-calibration study or bone mineral density (BMD) comparison is done between facilities; and (4) the minimum acceptable precision for an individual technologist. We present here the ISCD Official Positions on these topics that were established as a result of the 2005 PDC, together with the associated rationales and supportive evidence.

Bone density in a population-based cohort of premenopausal adult women with early onset inflammatory bowel disease

OBJECTIVE

We aimed to determine the bone mineral density (BMD) using dual energy x-ray absorptiometry in a population-based sample of women with inflammatory bowel disease who were diagnosed before age 20 yr and who are currently premenopausal and less than 45 yr.

METHODS

The University of Manitoba Inflammatory Bowel Disease Epidemiology Research Registry was accessed to find eligible women. Of 171 eligible subjects, 82 agreed to participate, and 70 appeared for dual energy x-ray absorptiometry. All subjects completed demographic, clinical, and lifestyle questionnaires and underwent dual energy x-ray absorptiometry with analyses for both areal and volumetric BMD.

RESULTS

The mean areal T scores at the lumbar spine, femoral neck, total hip, and total body were -0.14 +/- 1.05, -0.15 +/- 1.04, -0.25 +/- 1.17, and +0.09 +/- 1.04, respectively. Forty-five subjects had normal BMD, and 25 had a T score < -1. There were no significant differences between these groups for predictive variables. Only three (4%) had osteoporosis (T score < -2.5 at any site). There were 12 with disease onset before puberty and 58 after puberty. There were no differences between these groups for BMD. Volumetric BMD was slightly higher than areal BMD at the lumbar spine (p < 0.0002), femoral neck (p < 0.01), and total hip (p < 0.001).

CONCLUSIONS

In a population-based sample of women diagnosed with IBD before 20 yr of age and who are currently premenopausal, their average BMD is normal and the prevalence of osteoporosis is very low. Despite the potential for children with IBD to develop osteoporosis, their BMD as adults is generally normal.

Bone turnover and body weight relationships differ in normal-weight compared with heavier postmenopausal women

Low body weight is associated with increased risk for fractures, whereas higher body weight has been shown to be protective against osteoporosis. This study evaluated whether body weight plays a role regulating bone turnover and mass in normal-weight (body mass index (BMI) <25 kg/m2), overweight (BMI 25-29.9 kg/m2) and obese (BMI> or =30 kg/m2) postmenopausal women who were either receiving hormone replacement therapy [HRT(+)] or not [HRT(-)] (total of six groups). Body weight, BMI, total body bone mineral content (TBBMC), and markers of bone formation (serum osteocalcin) and bone resorption (urinary pyridinoline (PYD) and deoxypyridinoline) were retrospectively analyzed in 210 postmenopausal women. The mean age was 67+/-6 years, with mean body weight of 70.8+/-14.2 kg, ranging from 45.0 to 115.5 kg. Body weight was positively correlated with TBBMC ( r=0.50, p<0.0001). There was a lower TBBMC and higher bone formation rate in normal-weight than obese HRT(-) women, but in women taking HRT there were no differences between BMI categories. In addition, in normal-weight HRT(-) women only, PYD and body weight showed a negative correlation (r=-0.39, p=0.01). Among normal-weight, but not overweight or obese subjects, we observed higher TBBMC and lower bone turnover in the HRT(+) compared with the HRT(-) group. Regression models explained 36% of the variance in TBBMC, mainly through body weight. Additional models could only explain 11-15% of the variance in bone turnover. Taken together, these data suggest that among normal-weight but not obese postmenopausal women, higher bone turnover is associated with lower bone mass, and that only normal-weight women show a different bone turnover profile with HRT treatment. Body weight should be considered an important factor in bone metabolism with relevant clinical implications.

Further validation of a questionnaire to identify women likely to have low bone density

A questionnaire instrument called the Simple Calculated Osteoporosis Risk Estimation (SCORE*) stratifies risk for osteoporosis, potentially reducing population-screening costs. SCORE is calculated using race, weight, age, history of estrogen use, fracture history, and presence/absence of rheumatoid arthritis. We tested SCORE in 912 postmenopausal women aged 45 yr or more using a Hologic QDR4500C densitometer for the total hip, femoral neck, and lumbar spine. National Health and Nutrition Examination Survey (NHANES III) norms were used to calculate hip T-scores. Low bone density (T-score < -2.0) was found in 29.6% of patients at the femoral neck, 17.7% at the total hip, 36.1% at the lumbar spine, and 46.1% at one or more sites. The sensitivity/specificity of the SCORE model (using a threshold of 6 points) was 0.97/0.36 for the femoral neck, 0.95/0.30 for the total hip, 0.86/0.35 for the spine, and 0.88/0.41 for any site (total hip, femoral neck, or spine). When used to detect low bone density at any site, SCORE would have deferred 27.6% of women referred for DXA scans, but 20.7% of these (5.7% of the entire population) would have been false-negatives, and thus inappropriately deferred. At a cutpoint of 3 instead of 6, sensitivity/specificity was 0.96/0.16. In those aged 50-60, the group with the greatest need for risk stratification, sensitivity/specificity for low density at any site was 0.72/0.54, and 46.1% would have been deferred, but 18.5% of this group would have been false-negatives. A cutpoint of 1 in this age group yielded sensitivity/specificity of 0.94/0.16. After age 65, few women would be deferred.

CONCLUSION

When used to detect low bone density at any site with sufficient sensitivity for clinical practice, SCORE did not have sufficient discriminatory power to be broadly applicable.