Absolute fracture risk varies with bone densitometry technique used. A theoretical and in vivo study of fracture cases

Osteoporosis in a female population from Bratislava--age-related BMD changes

PATIENTS AND METHODS

We analysed 498 women (n=498) in a Bratislava (BA) population aged 21 to 90. We measured bone mineral density (BMD) in the proximal femur with one densitometric instrument (DXA Osteocore II, France; dual energy X-ray absorptiometry), applying BMD and T-score values in three standard regions of interest: Neck (ROI1), Ward's area (ROI2), Trochanter (ROI3).

RESULTS

Measured values of T-score in ROI1, ROI2 had normal distribution and a lognormal distribution of frequency in ROI3. Using chi2-test (chi-square goodness-of-fit statistics), we determined the distribution of the frequency of T-score values and the percentage of osteoporosis incidence in the Bratislava female population. The osteoporosis incidence, according to T-score values measured in ROI1 was 2.40%, in ROI2 16.34% and in ROI3 3.83%. Following the division of women into ten-year intervals, the statistically significant sample averages of T-score values were decreasing in relation to age only for ROI2. Osteoporosis incidence in age intervals was rising with age for ROI2, for ROI1 the number of osteoporotic patients in the 61 to 70-year interval was lower than in the 41 to 50-year interval, and for ROI3 the number of osteoporotic patients in the 51 to 60-year interval was lower than in the 41 to 50-year interval. Except in the above-mentioned intervals, T-score values decreased in relation to age also in ROI1 and ROI3. According to the analysis of variance, the age category explains 9.6% of the overall variability of T-score values for ROI1, 24.7% for ROI2 and 11.70% for ROI3.

CONCLUSIONS

As in ROI2 (Ward's area) a greater fraction of trabecular bone is measured in comparison with ROI1 and ROI3, ROI2 reflects best the age-related BMD changes. In ROI1 and ROI3 the relation was distorted by a greater fraction of cortical bone in comparison with ROI2 and by osteoarthritis.

T-plus Z-score in the assessment of relative fracture risk

THE OBJECTIVE OF THE STUDY: We aimed to prove that the relative risk of fractures (RR) is higher in women whose T- and Z-score values come under the category of increased risk than in the women whose T-score only falls within the category of increased risk.

PATIENTS AND METHODS

We analysed 498 (n=498) densitometric findings from the area of proximal femur: neck (ROI1), Ward's area (ROI2), great trochanter (ROI3) (DXA-dual energy X-ray absorptiometry, Osteocore II, France) from a population of Bratislava women of an average age of 59.71 years <58.63; 60.80>. Measured values of T- and Z-score were categorized as follows: 1--increased fracture risk (T-score<-2.5 SD/T=1, Z-score<or=-1.0 SD/Z=1), 0-without increased fracture risk (T-score>-2.5 SD/T=0, Z-score>-1.0 SD/Z=0).

RESULTS

RR for development of fracture was higher for all measurement sites (ROI(1)-29.87; ROI(2)-15.3; ROI(3)-5.5) for women having T-score<-2.5 SD and simultaneously Z-score<or=-1.0 SD than for the women having T-score<-2.5 SD and simultaneously Z-score>-1.0 SD. When the women were divided according to age into two groups, it was found that the RR of fracture for women<65 years having a T-score<-2.5 SD and also a Z-score<or=-1.0 SD is very high (RR=infinity), elderly women (>or=65 years) had a RR for ROI(1)-32.61, for ROI(2)-7.72, and for ROI(3)-6.9. The probability (P) of the presence of women with T-score values<-2.5 SD and Z-score<or=-1.0 SD in the group under 65 years for ROI1 was 12.5%; for ROI2 34.4%; for ROI3 20.5%, and the probability for women>or=65 years was for ROI1 75%; ROI2 98% and for ROI3 100%.

CONCLUSIONS

The study's contribution lies in the finding that the relative fracture risk of the proximal femur in women increases if the T-score is <-2.5 SD and, simultaneously, the Z-score<or=-1.0 SD, this risk is especially high for women under the age of 65. In assessing the individual fracture risk in female patients we recommend to add also Z-score values in the measured area to T-score values and to other anamnestic and biochemical risk factors.

Guidelines for the diagnosis of osteoporosis: T-scores vs fractures

The development of bone mineral densitimometry methodologies, especially central dual energy X-ray absorptiometry (DXA) methods have allowed this quantitative tool to be used to diagnose osteoporosis before the first fragility fracture has occurred. The World Health Organization osteoporosis working group set the stage for the BMD cut-off criteria development. The wide application of DXA has brought the treatment of osteoporosis to the primary care level, a very necessary step if this increasingly prevalent disease is to have a decline in its incidence. The most difficult osteoporosis cases, for which there are many and their associated difficult DXA results and interpretation will always require specialists' involvement. In particular, the embracement of the WHO absolute fracture risk validated project will take DXA to a much greater level of value in making management decisions. In particular, the WHO absolute risk data will allow physicians, health-economic policy makers, and payors of medical services to come closer together to decide which patients are at a level of unacceptable fracture risk that justifies treatment intervention. The implementation of this validated project will also remove the unacceptable subjective computer printouts on DXA reports that often lead to the over-treatment of low risk patients and at times the under-treatment of high risk patients. The evolution of the clinical interpretation of bone densitometry has been a work in progress. Challenges in the clinical measurement of bone strength remain and will also evolve. The field of osteoporosis has grown with the use of DXA and will continue to embrace this technology as other technologies to measure fracture risk become applied in clinical practice.

Device-specific thresholds to diagnose osteoporosis at the proximal femur: an approach to interpreting peripheral bone measurements in clinical practice

INTRODUCTION

A single T score criterion cannot be universally applied to different peripheral bone measurement devices, since measurements in an identical population result in a tenfold difference in the prevalence of osteoporosis. The use of peripheral devices is increasing in clinical practice, despite the difficulties in interpreting results. We propose the use of two thresholds, which have either 95% sensitivity or 95% specificity, to identify (1) individuals who require treatment or (2) individuals who require no treatment, both based on a peripheral measurement alone, or (3) individuals who require additional central densitometry measurements.

METHODS

We recruited 500 postmenopausal women, 100 premenopausal women and 279 women with proximal femoral, vertebral, distal forearm or proximal humeral fractures. All subjects underwent dual energy X-ray absorptiometry (DXA) measurements of the lumbar spine, total hip and distal forearm, quantitative computed tomography (QCT) of the distal forearm and quantitative ultrasound (QUS) of the heel (four devices), finger (two devices), radius and metatarsal. We identified the threshold for each device that identified women without osteoporosis with the same sensitivity (upper threshold set at 95%) as total hip DXA and women with osteoporosis with the same specificity (lower threshold set at 95%) as total hip DXA. Individuals between the two thresholds required additional examination by central densitometry.

RESULTS

The correlation between devices varied from 0.173 (QUS finger) to 0.686 (DXA forearm) compared with total hip DXA (P<0.0001). The area under the curve (AUC) between devices varied from 0.604 (QUS finger) to 0.896 (DXA forearm) compared with total hip DXA (P<0.0001). In a population-based cohort (prevalence of osteoporosis 9.8%) the threshold approach appropriately identified between 26% (QUS heel) and 68% (DXA forearm) of subjects in whom a treatment decision could be made without additional central DXA with 95% certainty. In a fracture cohort (prevalence of osteoporosis 36%) between 16% (QUS finger) and 37% (QCT forearm) of subjects were appropriately identified.

CONCLUSION

The threshold approach to interpreting peripheral bone measurements enables a substantial number of individuals with either normal bone mineral density (BMD) or osteoporosis to be selected and treated appropriately.

Low BMD is a risk factor for low-energy Colles' fractures in women before and after menopause

Until now, it was unclear if low volumetric bone mineral density at the distal radius was also a risk factor for Colles' fracture, especially in patients with low-energy trauma. In our study, we used peripheral quantitative computed tomography to measure volumetric bone mineral density of a nonfractured distal radius and dual-energy x ray absorptiometry to measure areal bone mineral density at the spine and hip in patients with Colles' fractures, including 45 women who were premenopausal (age range, 40-50 years) and 39 women who were postmenopausal (age range, 51-65 years). In each group, the patients were subdivided into low-energy and high-energy fracture groups. Ninety-five age-matched healthy women who were premenopausal and 90 age-matched healthy women who were postmenopausal without fracture history served as controls. The results showed that patients with low-energy fractures had a lower bone mineral density at all measurement sites, compared with either patients with high-energy fractures or control subjects. More patients were found with a bone mineral density less than -2.5 standard deviations (Z-score) in the premenopausal group (12.5% measured by dual-energy x ray absorptiometry and 41.2% measured by peripheral quantitative computed tomography) than in the postmenopausal group (6.0% measured by dual-energy x ray absorptiometry and 4.8% measured by peripheral quantitative computed tomography). These results suggest that low bone mineral density, particularly measured using peripheral quantitative computed tomography at the distal radius of women who were premenopausal, was an important risk factor for low-energy Colles' fractures.

LEVEL OF EVIDENCE

Prognostic study, Level I-1 (prospective study). See the Guidelines for Authors for a complete description of levels of evidence.