Lateral dual X-ray absorptiometry of the lumbar spine: current status

Subregional DXA-derived vertebral bone mineral measures are stronger predictors of failure load in specimens with lower areal bone mineral density, compared to those with higher areal bone mineral density

Measurement of areal bone mineral density (aBMD) in intravertebral subregions may increase the diagnostic sensitivity of dual-energy X-ray absorptiometry (DXA)-derived parameters for vertebral fragility. This study investigated whether DXA-derived bone parameters in vertebral subregions were better predictors of vertebral bone strength in specimens with low aBMD, compared to those with higher aBMD. Twenty-five lumbar vertebrae (15 embalmed and 10 fresh-frozen) were scanned with posteroanterior- (PA) and lateral-projection DXA, and then mechanically tested in compression to ultimate failure. Whole-vertebral aBMD and bone mineral content (BMC) were measured from the PA- and lateral-projection scans and within 6 intravertebral subregions. Multivariate regression was used to predict ultimate failure load by BMC, adjusted for vertebral size and specimen fixation status across the whole specimen set, and when subgrouped into specimens with low aBMD and high aBMD. Adjusted BMC explained a substantial proportion of variance in ultimate vertebral load, when measured over the whole vertebral area in lateral projection (adjusted R (2) 0.84) and across the six subregions (ROIs 2-7) (adjusted R (2) range 0.58-0.78). The association between adjusted BMC, either measured subregionally or across the whole vertebral area, and vertebral failure load, was increased for the subgroup of specimens with identified 'low aBMD', compared to those with 'high aBMD', particularly in the anterior subregion where the adjusted R (2) differed by 0.44. The relative contribution of BMC measured in vertebral subregions to ultimate failure load is greater among specimens with lower aBMD, compared to those with higher aBMD, particularly in the anterior subregion of the vertebral body.

Chronic low back pain is associated with reduced vertebral bone mineral measures in community-dwelling adults

Background

Chronic low back pain (CLBP) experienced in middle-age may have important implications for vertebral bone health, although this issue has not been investigated as a primary aim previously. This study investigated the associations between CLBP and dual energy X-ray absorptiometry (DXA)-derived vertebral bone mineral measures acquired from postero-anterior and lateral-projections, among community-dwelling, middle-aged adults.

Methods

Twenty-nine adults with CLBP (11 male, 18 female) and 42 adults with no history of LBP in the preceding year (17 male, 25 female) were evaluated. Self-reported demographic and clinical data were collected via questionnaires. Areal bone mineral density (aBMD) was measured in the lumbar spine by DXA. Apparent volumetric (ap.v) BMD in the lumbar spine was also calculated. Multiple linear regression models were used to examine associations between study group (CLBP and control) and vertebral DXA variables by gender, adjusting for height, mass and age.

Results

There was no difference between groups by gender in anthropometrics or clinical characteristics. In the CLBP group, the mean (SD) duration of CLBP was 13.3 (10.4) years in males and 11.6 (9.9) years in females, with Oswestry Disability Index scores of 16.2 (8.7)% and 15.4 (9.1)%, respectively. Males with CLBP had significantly lower adjusted lateral-projection aBMD and lateral-projection ap.vBMD than controls at L3 with mean differences (standard error) of 0.09 (0.04) g/cm² (p = 0.03) and 0.02 (0.01) g/cm³ (p = 0.04). These multivariate models accounted for 55% and 53% of the variance in lateral-projection L3 aBMD and lateral-projection L3 ap.vBMD.

Conclusions

CLBP in males is associated with some lumbar vertebral BMD measures, raising important questions about the mechanism and potential clinical impact of this association.

Diagnosis of osteoporosis: visual assessment on conventional versus digital radiographs

In many radiological departments conventional radiography has been replaced by digital radiography. Therefore, the purpose of this study was to analyze the visual detection of osteopenia/osteoporosis with both digital and conventional radiographs. In 286 patients we retrospectively evaluated radiographs of the lumbar spine in two planes. One hundred twenty-eight patients had conventional and 158 patients had digital radiographs. Patients with pre-existing vertebral fractures were excluded. Four experienced musculoskeletal radiologists blinded to the values of DXA and to the patients' ages assessed independently from each other whether the bone density of the lumbar spines was normal or decreased. The results of dual X-ray absorptiometry served as the standard of reference. The threshold value for the diagnosis of osteopenia was a T-score less than -1 SD according to the WHO classification of osteoporosis. Sensitivity/specificity was 86%/36% for conventional and 72%/47% for digital radiographs. The overall diagnostic accuracy was 68% for conventional and 64% for digital radiographs. Eighty percent of the patients with osteopenia and 96% of the patients with osteoporosis were correctly assessed as true positive on conventional radiographs and 65% (osteopenia) and 82% (osteoporosis) on digital radiographs. Interobserver agreement was markedly lower for digital (35%) than for conventional radiographs (73%). However, the differences were not statistically significant. There is no major difference in diagnostic accuracy in the assessment of osteopenia/osteoporosis using digital and conventional radiographs, respectively. However, the high interobserver variance on digital radiographs indicates that visual assessment of osteoporosis/osteopenia is problematic, which may be due to image processing and postprocessing algorithms that manipulate the visual aspect of bone density.

In vivo intrarater and interrater precision of measuring apparent bone mineral density in vertebral subregions using supine lateral dual-energy x-ray absorptiometry

Analysis of apparent bone mineral density (BMD) in the lumbar spine is commonly based on anteroposterior (AP) scanning using dual-energy X-ray absorptiometry (DXA). Although not widely used, clinically important information can also be derived from lateral scanning. Vertebral bone density, and therefore strength, can may vary in different subregions of the vertebral body. Therefore, subregional BMD measurements might be informative about fracture risk. However, the intrarater and interrater precision of in vivo subregional BMD assessments from lateral DXA remains unknown. Ten normal, young (mean: 24 yr) and 10 older (mean: 63 yr) individuals with low BMD were scanned on one occasion using an AP/lateral sequence. Each lateral scan was reanalyzed six times at L2 by three raters to determine the intrarater and interrater precision in selecting seven regions of interest (subregions). Precision was expressed using percentage coefficients of variation (% CV) and intraclass correlation coefficients (ICC). Intrarater precision ranged from ICC(1,1) 0.971 to 0.996 (% CV: 0.50-3.68) for the young cohort and ICC(1,1) 0.934 to 0.993 (% CV: 1.46-5.30) for the older cohort. Interrater precision ranged from ICC(2,1) 0.804 to 0.915 (% CV: 1.11-2.35) for the young cohort and ICC(2,1) 0.912 to 0.984 (% CV: 1.85-4.32) for the older cohort. Scanning a subgroup of participants twice with repositioning was used to assess short-term in vivo precision. At L2, short-term in vivo precision ranged from ICC(1,1) 0.867 to 0.962 (% CV: 3.38-9.61), at L3 from ICC(1,1) 0.961 to 0.988 (% CV: 2.02-5.57) and using an L2/L3 combination from ICC(1,1) 0.942 to 0.980 (% CV: 2.04-4.61). This study demonstrated moderate to high precision for subregional analysis of apparent BMD in the lumbar spine using lateral DXA in vivo.

Effects of projective bone area size of the spine on bone density and the diagnosis of osteoporosis in healthy pre-menopausal women in China

The aim of this study was to understand the effects of projective bone area (BA) size of the spine on bone density and the diagnosis of osteoporosis. Measurements of BA, bone mineral content (BMC), areal bone density (aBMD) and volumetric bone density (vBMD) at the posteroanterior (PA) lumbar spine (vertebrae L2-L4) followed by a paired PA/lateral spine (L2-L4) were made using a dual-energy X-ray absorptiometry (DXA) fan-beam bone densitometer (Hologic QDR 4500A) in 1436 healthy pre-menopausal women aged from 20 to 56-years-old. At the PA and lateral lumbar spine, there was a significant positive correlation between BA and BMC (r=0.762 and 0.762, p=0.000) and aBMD (r=0.370 and 0.352, p=0.000), but not vBMD (r=0.000 and 0.102, p=0.813 and 0.063). When BA at the PA spine changed by one standard deviation (SD), BMC and aBMD correspondingly changed by 12.6% and 4.3% on the basis of their respective means while vBMD indicated no change. When a variation of 1 SD was observed in BA at the lateral spine, BMC, aBMD and vBMD correspondingly changed by 13.8%, 4.4% and 1.73% on the basis of their respective means. Through an intercomparison among large, intermediate and small BA groups, significant differences were found in the means of subject's height, weight, BMC and aBMD at the PA and lateral spine as well as the detection rate of osteoporosis by aBMD (p=0.000). Detection rates of osteoporosis by aBMD at the PA, lateral spine and vBMD in healthy pre-menopausal women aged from 40 years to 56 years were 4.5%, 16.4% and 9.7%, respectively, in the small BA group; 1.3%, 6.4% and 7.3%, respectively, in the intermediate BA group; and 0, 0 and 5.5%, respectively, in the large BA group. No significant differences were found in the detection rates of osteoporosis by vBMD among the groups. The results of multiple linear regression revealed that the major factors influencing BA of the lumbar spine was height. In healthy pre-menopausal women of the same race and age, the BA size of the lumbar spine would have significant influence upon aBMD and the diagnosis of osteoporosis, i.e. the larger the BA, the greater the aBMD and the lower the osteoporosis detection rate while conversely, the smaller the BA, the smaller the aBMD and the higher the osteoporosis detection rate. Though vBMD does not change with BA sizes of the lumbar spine, it is a sensitive marker for diagnosing osteoporosis.

Effects of a low-dose and ultra-low-dose combined oral contraceptive use on bone turnover and bone mineral density in young fertile women: a prospective controlled randomized study

In this prospective, controlled, randomized study, we compared the effect of a low-dose 21-day combined oral contraceptive (COC) containing 20 microg ethinyl estradiol (EE) and 75 microg gestodene (GTD) (Group A; n = 19) with an ultra-low-dose 24-day COC containing 15 microg EE and 60 microg GTD (Group B; n = 18) on bone turnover and bone mineral density (BMD) in young, fertile women. Nineteen healthy fertile women were used as untreated controls (Group C). At 3, 6, 9 and 12 months of the study serum osteocalcin (BGP), urinary pyridinoline (PYD) and deoxypyridinoline (D-PYD) were measured in all subjects. At baseline and after 12 months BMD was determined at lumbar spine by dual-energy X-ray absorptiometry in all patients. In both Groups A and B, urinary levels of PYD and D-PYD at 6, 9 and 12 months, were significantly reduced in comparison with basal values and with control subjects (p < 0.05). No significant differences in urinary PYD and D-PYD levels were observed between Groups A and B during the entire period of treatment. At 12 months, no statistically significant difference in spinal BMD values was detected between the three groups and in comparison with basal values. The present study suggests that the two COCs could exert a similar positive effect on bone turnover in young postadolescent women, without any significant and appreciable modification of BMD.

Bone mineral density, osteopenia, and osteoporosis in the rhesus macaques of Cayo Santiago

This cross-sectional study investigates metabolic bone disease and the relationship between age and bone mineral density (BMD) in males and females of a large, well-documented skeletal population of free-ranging rhesus monkeys (Macaca mulatta), from the Caribbean Primate Research Center Museum collection from Cayo Santiago, Puerto Rico. The sample consists of 254 individuals aged 1.0-20+ years. The data consist of measurements of bone mineral content and bone mineral density, obtained from dual-energy X-ray absorptiometry (DEXA), of the last lumbar vertebra from each monkey. The pattern of BMD differs between male and female rhesus macaques. Females exhibit an initial increase in BMD with age, with peak bone density occurring around age 9.5 years, and remaining constant until 17.2 years, after which there is a steady decline in BMD. Males acquire bone mass at a faster rate, and attain a higher peak BMD at an earlier age than do females, at around 7 years of age, and BMD remains relatively constant between ages 7-18.5 years. After age 7 there is no apparent effect of age on BMD in the males of this sample; males older than 18.5 years were excluded due to the presence of vertebral osteophytosis, which interferes with DEXA. The combined frequency of osteopenia and osteoporosis in this population is 12.4%. BMD values of monkeys with vertebral wedge fractures are generally higher than those of virtually all of the nonfractured osteopenic/osteoporotic individuals, thus supporting the view that BMD as measured by DEXA is a useful but imperfect predictor of fracture risk, and that low BMD may not always precede fractures in vertebral bones. Other factors such as bone quality (i.e., trabecular connectivity) should also be considered. The skeletal integrity of a vertebra may be compromised by the loss of key trabeculae, resulting in structural failure, but the spine may still show a BMD value within normal limits, or within the range of osteopenia.

Central region-of-interest analysis of lumbar spine densitometry demonstrates lower bone mass in older rhesus monkeys

Osteoarthritis (OA) spuriously elevates spine bone mineral density (BMD) as measured by dual-energy X-ray absorptiometry (DXA). This study documents spinal OA prevalence in adult female rhesus monkeys, and evaluates a custom central region-of-interest (CROI) analysis technique designed to minimize OA effects on BMD measurement. Lumbar spine radiographs were obtained on 71 animals, age 10-37 years. OA degree was blindly scored as none, minimal, or moderate/severe. Moderate/severe OA was not observed before age 19, but was present in 66% of older animals. Subsequently, lumbar spine (L2-4) BMD was determined by standard DXA analysis and manual placement of 0.92 cm2 CROIs in two groups of female rhesus monkeys. One group (eight control, eight postovariectomy, ages 10-19 years) was assessed longitudinally, the second (n = 90, ages 10-37) cross-sectionally. Measured bone loss following ovariectomy (8.1% standard analysis, 11.5 % CROI) was comparable with both techniques. By contrast, CROI demonstrated lower bone mass with age (p < 0.0001), whereas only a trend (p = 0.06) was observed with standard analysis. When World Health Organization criteria were applied, 42% of animals > or = age 19 years were classified as osteopenic/osteoporotic by standard analysis compared with 67% by CROI. All "normal" animals reclassified as osteopenic/osteoporotic by CROI had OA. In conclusion, female rhesus monkeys often develop spinal OA with advancing age. CROI analysis demonstrated lower bone density in older monkeys and was as sensitive to estrogen-depletion bone loss as standard methodology. This suggests that alternative analysis techniques, such as CROI, may be more appropriate to evaluate bone density in nonhuman primates, and potentially in people.

Vertebral bone density evaluated by dual-energy X-ray absorptiometry and quantitative computed tomography in vitro

Vertebral bone density is evaluated mainly by dual-energy X-ray absorptiometry (DXA) or quantitative computed tomography (QCT). Densitometry is used as an estimator of bone strength and forms the basis for choice of treatment. DXA expresses bone density in grams per square centimeter (area density) and QCT expresses bone density in milligrams per cubic centimeter (volumetric density). The aim of this study was to identify the differences between the two techniques, DXA and QCT, when applied to a group of female and male subjects over a wide age range. The data consisted of 221 lumbar vertebral bodies (L3 and L4) excised at autopsy. There were 90 females with a mean age of 65.6 (range 18-94) years and 131 males with a mean age of 62.0 (range 21-94) years. The vertebrae were scanned en bloc in demineralized water in Plexiglas containers with both DXA and QCT. DXA was performed using posteroanterior (PA) and lateral projection. QCT was performed in the center of each vertebra with 1 cm slice thickness. Both methods showed decreasing bone density with age. Lateral DXA showed a decrease in bone density with age from approximately 0.8 g/cm2 to approximately 0.4 g/cm2. QCT showed a decrease in bone density with age from approximately 180 mg/cm3 to approximately 30 mg/cm3. Lateral DXA bone mineral densities (BMD) were correlated with QCT densities in both females (r2 = 0.68, p < 0.00001) and males (r2 = 0.53, p < 0.00001), but females had constantly lower DXA BMDs than males at a given QCT density. QCT and width-adjusted midlateral DXA (g/cm3) were significantly correlated, with r2 = 0.64 (p < 0.00001) for females and r2 = 0.61 (p < 0.00001) for males. In conclusion, age- and gender-related differences in human vertebral bone density were shown to be dependent on the scanning method used. DXA bone mineral content (BMC) and BMD showed that females had lower values than males at all ages. When the "volumetric" DXA measurements and QCT were used, the females had the highest densities in the younger decades and males had the highest densities in the oldest decades. Finally, the area density (BMD) measured by DXA was lower in females than in males with identical QCT volumetric bone densities.