Bone density at various sites for prediction of hip fractures. The Study of Osteoporotic Fractures Research Group

Women with low bone density in the radius or calcaneus are at increased risk of hip fracture. To see whether bone density of the hip measured by dual X-ray absorptiometry is a better predictor of hip fracture than measurements of other bones, we assessed bone density at several sites in 8134 women aged 65 years or more. 65 women had hip fractures during a mean follow-up of 1.8 years. Each SD decrease in femoral neck bone density increased the age-adjusted risk of hip fracture 2.6 times (95% CL 1.9, 3.6). Women with bone density in the lowest quartile had an 8.5-fold greater risk of hip fracture than those in the highest quartile. Bone density of the femoral neck was a better predictor than measurements of the spine (p < 0.0001), radius (p < 0.002), and moderately better than the calcaneus (p = 0.10). Low hip bone density is a stronger predictor of hip fracture than bone density at other sites. Efforts to prevent hip fractures should focus on women with low hip bone density.

Rapid loss of vertebral mineral density after renal transplantation

BACKGROUND

Osteopenia is a major complication of renal transplantation. Immunosuppressive regimens including cyclosporine, which permit the use of lower doses of glucocorticoids, may reduce glucocorticoid-induced osteopenia.

METHODS

We prospectively studied the magnitude, distribution, and mechanism of bone loss in 20 adults who received renal allografts from living related donors, who had good renal function, and who were treated with azathioprine, cyclosporine, and low doses of prednisone. We measured serum biochemical markers of bone metabolism, determined the bone mineral density of the second, third, and fourth lumbar vertebrae and the shaft of the radius, and analyzed the histomorphometric features of iliac bone at the time of transplantation and six months later. Measurements of vertebral mineral density were repeated 18 months after transplantation in 17 of the patients.

RESULTS

After transplantation, the mean serum concentrations of parathyroid hormone, phosphorus, and alkaline phosphatase decreased and the serum calcitriol concentration increased. The mean (+/- SD) bone mineral density of the vertebrae had decreased 6.8 +/- 5.6 percent 6 months after transplantation (P less than 0.05) and 8.8 +/- 7.0 percent 18 months after transplantation. In contrast, the bone mineral density of the radius had increased six months after transplantation (P less than 0.05). The histomorphometric studies showed that the rate of bone formation decreased from 50.5 +/- 44.8 to 23.1 +/- 13.8 microns3 per square micrometer per year (P less than 0.05), and the formation period lengthened from 70 +/- 42 to 146 +/- 144 days (P less than 0.05). Consequently, the amount of bone replaced during a remodeling cycle diminished.

CONCLUSIONS

Osteopenia associated with renal transplantation remains a problem in the cyclosporine era. The loss of vertebral bone in our subjects was due to an imbalance in bone remodeling consistent with a toxic effect of glucocorticoids.

Osteopenia in men with a history of delayed puberty

BACKGROUND AND METHODS

The effect of delayed puberty on peak bone mineral density in men is unknown. To determine whether such a delay reduces normal peak bone density and leads to osteopenia during adulthood, we measured radial bone mineral density by single-photon absorptiometry and spinal bone mineral density by dual-energy x-ray absorptiometry in 23 men who had a history of constitutionally delayed puberty and 21 men who underwent normal puberty. Their mean ages were 26 and 24 years, respectively. The groups were matched for other factors known to affect bone mass.

RESULTS

The mean (+/- SD) radial bone mineral density was significantly lower in the men with a history of delayed puberty than in the normal men (0.73 +/- 0.07 vs. 0.80 +/- 0.05 g per square centimeter; P less than 0.0002). Spinal bone mineral density was also significantly lower in the men with delayed puberty than in the normal men (1.03 +/- 0.10 vs. 1.13 +/- 0.11 g per square centimeter; P less than 0.003). Radial bone density was at least 1 SD below the mean value for the normal men in 15 of the 23 men with a history of delayed puberty, and spinal bone density was similarly decreased in 10 of the 23.

CONCLUSIONS

Adult men with a history of constitutionally delayed puberty have decreased radial and spinal bone mineral density. These findings suggest that the timing of puberty is an important determinant of peak bone density in men. Because the peak bone mineral density achieved during young adulthood is a major determinant of bone density in later life, men in whom puberty was delayed may be at increased risk for osteoporotic fractures when they are older.

Muscle atrophy and bone loss after 90 days' bed rest and the effects of flywheel resistive exercise and pamidronate: results from the LTBR study

Muscle atrophy and bone loss pose substantial problems for long-term space flight and in clinical immobilization. We therefore tested the efficacy of flywheel resistive exercise and pamidronate to counteract such losses. Twenty five young healthy males underwent strict bed rest with -6 degrees head-down tilt for 90 days. Subjects were randomized into an exercise group that practiced resistive exercise with a 'flywheel' (FW) device every 2-3 days, a pamidronate group (Pam) that received 60 mg pamidronate i.v. 14 days prior to bed rest and a control group (Ctrl) that received none of these countermeasures. During the study, Ca(++) and protein intake were controlled. Peripheral quantitative computed tomography (pQCT) was used to assess bone mineral content (BMC) and muscle cross sectional area (mCSA) of calf and forearm. Measurements were taken twice during baseline data collection, after 28 and after 89 days bed rest, and after 14 days recovery. On the same days, urinary Pyridinoline excretion and serum levels of alkaline phosphatase, Ca(++) and PTH were measured. Pre-study exercise habits were assessed through the Freiburg questionnaire. Losses in calf mCSA were significantly reduced in FW (Ctrl: -25.6% +/- 2.5% Pam: -25.6% +/- 3.7%, FW: -17.3% +/- 2.7%), but not in the forearm mCSA (Ctrl: -6.4% +/- 4.33%, Pam: -7.7% +/- 4.1%, FW: -7.6% +/- 3.3%). Both diaphyseal and epiphyseal BMC losses of the tibia were mitigated in Pam and FW as compared to Ctrl, although this was significant only at the diaphysis. Inter-individual variability was significantly greater for changes in BMC than in mCSA, and correlation of BMC losses was poor among different locations of the tibia. A significant positive correlation was found between change in tibia epiphyseal BMC and serum cortisol levels. These findings suggest that both countermeasures are only partly effective to preserve BMC (FW and Pam) and mCSA (FW) of the lower leg during bed rest. The partial efficacy of flywheel exercise as well as the bones' response to unloading per se underlines the importance of mechanical stimuli. The huge variability of BMC changes, however, suggests that other factors affect changes in whole-bone strength following acute mechanical disuse.

Cement lines of secondary osteons in human bone are not mineral-deficient: New data in a historical perspective

Using qualitative backscattered electron (BSE) imaging and quantitative energy dispersive X-ray (EDX) spectroscopy, some investigators have concluded that cement (reversal) lines located at the periphery of secondary osteons are poorly mineralized viscous interfaces with respect to surrounding bone. This conclusion contradicts historical observations of apparent highly mineralized (or collagen-deficient) cement lines in microradiographs. Such conclusions, however, may stem from unrecognized artifacts that can occur during scanning electron microscopy. These include specimen degradation due to high-energy beams and the sampling of electron interaction volumes that extend beyond target locations during EDX analysis. This study used quantitative BSE imaging and EDX analysis, each with relatively lower-energy beams, to test the hypothesis that cement lines are poorly mineralized. Undemineralized adult human femoral diaphyses (n = 8) and radial diaphyses (n = 5) were sectioned transversely, embedded in polymethyl methacrylate, and imaged in a scanning electron microscope for BSE and EDX analyses. Unembedded samples were also evaluated. Additional thin embedded samples were stained and evaluated with light microscopy and correlated BSE imaging. BSE analyses showed the consistent presence of a bright line (higher atomic number) coincident with the classical location and description of the cement line. This may represent relative hypermineralization or, alternatively, collagen deficiency with respect to surrounding bone. EDX analyses of cement lines showed either higher Ca content or equivalent Ca content when compared to distant osteonal and interstitial bone. These data reject the hypothesis that cement lines of secondary osteons are poorly mineralized.

Bone strength at clinically relevant sites displays substantial heterogeneity and is best predicted from site-specific bone densitometry

In this study we test the hypotheses that mechanical bone strength in elderly individuals displays substantial heterogeneity among clinically relevant skeletal sites, that ex situ dual-energy X-ray absorptiometry (DXA) provides better estimates of bone strength than in situ DXA, but that a site-specific approach of bone densitometry is nevertheless superior for optimal prediction of bone failure under in situ conditions. DXA measurements were obtained of the lumbar spine, the left femur, the left radius, and the total body in 110 human cadavers (age, 80.6 +/- 10.5 years; 72 female, 38 male), including the skin and soft tissues. The bones were then excised, spinal and femoral DXA being repeated ex situ. Mechanical failure tests were performed on thoracic vertebra 10 and lumbar vertebra 3 (compressive loading of a functional unit), the left and right femur (side impact and vertical loading configuration), and the left and right distal radius (fall configuration, axial compression, and 3-point-bending). The failure loads displayed only very moderate correlation among sites (r = 0.39 to 0.63). Ex situ DXA displayed slightly higher correlations with failure loads compared with those of in situ DXA, but the differences were not significant and relatively small. Under in situ conditions, DXA predicted 50-60% of the variability in bone failure loads at identical (or closely adjacent) sites, but only around 20-35% at distant sites, advocating a site-specific approach of densitometry. These data suggest that mechanical competence in the elderly is governed by strong regional variation, and that its loss in osteoporosis may not represent a strictly systemic process.

Bone mineral density by age, gender, pubertal stages, and socioeconomic status in healthy Lebanese children and adolescents

Gender, ethnicity, and lifestyle factors affect bone mass acquisition during childhood, thus the need for age- and sex-adjusted Z scores using ethnic-specific data for bone mineral density (BMD) measurement. This study aimed at establishing normative data for BMD in healthy Lebanese children and adolescents. Three hundred sixty-three healthy children aged 10 to 17 years (mean+/-SD: 13.1+/-2.0) were studied. BMD, bone mineral content (BMC), and lean mass were measured by dual-energy X-ray absorptiometry (DXA) using a Hologic 4500A device, and apparent volumetric BMD (BMAD) of the lumbar spine and the femoral neck were calculated. BMD, BMC, and BMAD were expressed by age groups and Tanner stages for boys and girls separately. There was a significant effect of age and puberty on all bone parameters, except at the femoral neck BMAD in boys. BMC and BMD were higher at cortical sites in boys, including subtotal body and hip; whereas, in girls, it was higher at a site more enriched in trabecular bone, namely the lumbar spine. At several skeletal sites, girls had significantly higher BMD adjusted for lean mass than boys. By the end of puberty, adolescents had a mean BMD that was 43-66% higher at the lumbar spine and 25-41% higher at cortical sites than pre-pubertal children, depending on the gender. Mean BMD values in the study group were significantly lower (P<0.01) than Western normative values, with Z scores ranging between -0.2 and -1.1. In both genders, children of lower socioeconomic status tended to have lower BMD than those from a higher socioeconomic background. This study allows additional insight into gender dimorphism in mineral accretion during puberty. It also provides a valuable reference database for the assessment of BMD in children with pubertal or growth disorders who are of Middle Eastern origin.

Tracking of bone mass and density during childhood and adolescence

CONTEXT

Whether a child with low bone mineral density (BMD) at one point in time will continue to have low BMD, despite continued growth and maturation, is important clinically. The stability of a characteristic during growth is referred to as "tracking."

OBJECTIVE

We examined the degree of tracking in bone mineral content (BMC) and BMD during childhood and adolescence and investigated whether tracking varied according to age, sexual maturation, and changes in growth status.

DESIGN

We conducted a longitudinal study with measurements at baseline and annually for 3 yr.

SETTING

The Bone Mineral Density in Childhood Study was conducted at five clinical centers in the United States.

STUDY PARTICIPANTS

A total of 1554 girls and boys, ages 6-16 yr at baseline, participated in the study.

MAIN OUTCOME MEASURES

Whole body, spine, hip, and forearm BMC and BMD were measured by dual-energy x-ray absorptiometry, and age-, sex-, and race-specific Z-scores were calculated. Deviation from tracking was calculated as the Z-score at yr 3 minus baseline.

RESULTS

Correlations between Z-scores at baseline and yr 3 ranged from 0.76-0.88. Among children with a Z-score below -1.5 at baseline, 72-87% still had a Z-score below -1 after 3 yr. Age, sexual maturation, and deviations in growth status (P < 0.01) were associated with deviation from tracking; however, tracking was strongly evident even after adjusting for the effects of age, maturation, and growth.

CONCLUSIONS

Bone density showed a high degree of tracking over 3 yr in children and adolescents. Healthy children with low bone density will likely continue to have low bone density unless effective interventions are instituted.

Bone density of élite female athletes with stress fractures

To investigate whether stress fractures occurring in élite female athletes are related to reductions in bone mineral density (BMD), we measured BMD in nine athletes with such fractures and nine athletes without fractures who were matched for age, weight, height and sport. BMD was measured in three regions: upper limbs (distal radius), axial skeleton (lumbar spine) and lower limbs (femoral neck) by photon absorptiometry. The number of menses per year was significantly less (P less than 0.04) and the age of menarche was significantly delayed (mean +/- SD; 16.1 +/- 0.4 v. 14.4 +/- 1.5 years, P less than 0.02) in the fracture group compared with the non-fracture group. There was no significant difference in BMD between the two groups at any of the measurement sites. Moreover although the fractures occurred mainly in lower limb bones, at sites characterised by predominantly cortical bone, all athletes had femoral neck BMD values within the 95% confidence limits for normal non-athletic women. We conclude that stress fractures in élite female athletes are largely independent of BMD.

Nocturnal oxytocin secretion is lower in amenorrheic athletes than nonathletes and associated with bone microarchitecture and finite element analysis parameters

OBJECTIVE

Preclinical data indicate that oxytocin, a hormone produced in the hypothalamus and secreted into the peripheral circulation, is anabolic to bone. Oxytocin knockout mice have severe osteoporosis, and administration of oxytocin improves bone microarchitecture in these mice. Data suggest that exercise may modify oxytocin secretion, but this has not been studied in athletes in relation to bone. We therefore investigated oxytocin secretion and its association with bone microarchitecture and strength in young female athletes.

DESIGN

Cross-sectional study of 45 females, 14-21 years (15 amenorrheic athletes (AA), 15 eumenorrheic athletes (EA), and 15 nonathletes (NA)), of comparable bone age and BMI.

METHODS

We used high-resolution peripheral quantitative CT to assess bone microarchitecture and finite element analysis to estimate bone strength at the weight-bearing distal tibia and non-weight-bearing ultradistal radius. Serum samples were obtained every 60  min, 2300-0700  h, and pooled for an integrated measure of nocturnal oxytocin secretion. Midnight and 0700  h samples were used to assess diurnal variation of oxytocin.

RESULTS

Nocturnal oxytocin levels were lower in AA and EA than in NA. After controlling for estradiol, the difference in nocturnal oxytocin between AA and NA remained significant. Midnight and 0700  h oxytocin levels did not differ between groups. At the tibia and radius, AA had impaired microarchitecture compared with NA. In AA, nocturnal oxytocin correlated strongly with trabecular and cortical microarchitecture, particularly at the non-weight-bearing radius. In regression models that include known predictors of microarchitecture in AA, oxytocin accounted for a substantial portion of the variability in microarchitectural and strength parameters.

CONCLUSIONS

Nocturnal oxytocin secretion is low in AA compared with NA and associated with site-dependent microarchitectural parameters. Oxytocin may contribute to hypoestrogenemic bone loss in AA.

Milk basic protein (MBP) increases radial bone mineral density in healthy adult women

We studied the effects of daily intake of milk basic protein (MBP) on radial bone mineral density (BMD) in healthy adult women. Thirty-three healthy women were randomly assigned to a 6-month trial with either placebo or MBP (40 mg per day). The radial BMD of each volunteer was measured at the beginning of and at six months after the trial. The mean BMD value at the 6th month in the MBP group increased significantly at both 1/6 and 1/10 portion from the distal end of the radius, whereas that in the control group did not. The BMD gain of each volunteer in the MBP group was significantly higher than that in the placebo group. Thus a daily MBP supplementation of 40 mg in healthy adult women can significantly increase radial BMD.

The peak bone mass of Hawaiian, Filipino, Japanese, and white women living in Hawaii

Our study compares the bone mass of Hawaiian, Filipino, Japanese, and white women living in Oahu, Hawaii. Eligible women ranged in age from 25 to 34; all had bone mass measurements at the spine, calcaneus, and proximal and distal radius. Their average bone mineral density (BMD) remained stable with age at all four bone sites, indicating that the age range 25-34 may represent the peak bone mass. Bone mass varied, however, between ethnicities; differences in BMD up to 11% were observed. The Hawaiian women had the greatest BMD, and whites had the second greatest BMD at the spine and calcaneus. The Japanese most frequently had the lowest BMD. Differences in body size partly explained the differences; most ethnic differences were reduced or eliminated after adjusting for height and weight. At the spine, the ethnic differences for BMD were also apparent with BMC and with vertebral area. Hawaiian and white women had greater values than Japanese or Filipino women. Differences at the proximal radius resembled the spine, except that whites had the widest proximal widths. The results were more complex for the distal radius. At the distal radius whites had the lowest BMD of the four ethic groups. The difference between whites and Hawaiians derived from the greater bone mineral content (BMC) of the Hawaiian women. By contrast, the difference between whites and the Japanese and Filipinos derived from the wider distal widths of the white women. Compared with the Japanese and Filipino women, the white women appeared to disperse their BMC at the distal radius across a wider bone width.(ABSTRACT TRUNCATED AT 250 WORDS)

An investigation of ethnic differences in bone mineral, hip axis length, calcium metabolism and bone turnover between West African and Caucasian adults living in the United Kingdom

The aim of the study was to investigate factors relating to calcium and bone metabolism which might explain the low incidence of osteoporotic fracture among Africans. Adult bone mineral status, hip axis length and biochemical indices were investigated in 20 Caucasians (10 male, 10 female) and 19 Gambians (12 male, 7 female) living in the UK. Bone mineral content (BMC), bone mineral density (BMD) and BMC adjusted for bone area, body weight and height (size-adjusted BMC) were measured for the whole-body, lumbar spine, femoral neck, trochanter, radius shaft and radius wrist using dual-energy X-ray absorptiometry. There were no significant differences in whole body or regional BMC; values tended to be lower in the Gambians. Gambian men had higher size-adjusted BMC at the femoral neck (Gambian-British = 21%, 95% CI = 6 to 36%, p < 0.01), associated with a smaller bone area (Gambian-British = -11%, 95% CI = -20 to -2%, p = 0.02). BMD was affected similarly. No other significant differences in BMD or size-adjusted BMC were observed. Gambians had shorter hip axis length (Gambian British, after accounting for sex, = -5%, 95% CI = -9 to -1%, p = 0.02). There were no significant differences in bone turnover (osteocalcin, bone isoenzyme of alkaline phosphatase, urinary deoxypyridinoline) or calciotropic hormone levels (parathyroid hormone, 1,25-dihydroxyvitamin D, calcitonin). Gambian men had lower 25-hydroxyvitamin D concentrations (Gambian = 26.3 SD 12.0 nmol/L, British = 55.5 SD 13.9 nmol/L, p < 0.0001), a difference not seen among the women. Gambian men and women excreted significantly less phosphate and potassium than British subjects by 30-60%; urinary calcium and sodium excretion were similar in the two groups. This study revealed few ethnic differences that could account for the disparity in osteoporotic fracture rates between Africans and Caucasians, with the possible exception of anatomical differences in the hip.

Menopausal bone loss is partially regulated by dietary intake of vitamin D

Five years ago we reported results from a cross-sectional study of the effect of nutritional factors on calcium-regulating hormones and bone loss in perimenopausal women. We found an inverse correlation between serum 25-hydroxyvitamin D (25OHD) and immunoreactive parathyroid hormone (PTH), and we postulated that over time, women with lower 25OHD would lose more bone because of increased bone remodeling induced by secondary hyperparathyroidism. We have followed 38 of these women for 5 years. Twenty-two have gone through menopause and we are reporting observations on these 22 subjects. Bone mineral analysis was performed twice a year at the distal and mid-radius using single-photon absorptiometry. The slope of the bone mineral content curve was calculated by least squares. Bone loss increased within 6 months of the rise in serum follicle stimulating hormone (FSH) to greater than 40 mIU/ml. We continued to see a negative correlation between 25OHD and PTH (r = -0.450, P = 0.03). Premenopause, PTH was negatively correlated with the proximal bone mineral content (PBMC) slope (-0.604, P = 0.002). The distal bone mineral content (DBMC) 5-year slope was correlated with dietary vitamin D (r = 0.509, P = 0.02), the higher the intake, the less negative the slope. The 5-year PBMC slope was negatively correlated with serum osteocalcin (OC) levels (r = -0.382, P = 0.08). Before menopause, the change in PBMC was positively correlated with OC (r = 0.450, P = 0.03). Postmenopause, the correlation with DBMC slope was negative (r = -0.506, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Bone mineral density of the spine and radius shaft in children with X-linked hypophosphatemic rickets (XLH)

X-linked hypophosphatemic rickets (XLH) is characterized by inadequate skeletal mineralization. The bone mineral density (BMD) of the radius shaft and the lumbar spine was determined in 13 children with XLH. Ten patients were on treatment, whereas three patients had discontinued treatment 20-32 months prior to this study. Two of them had radiological evidence of rickets. The radius shaft BMD was significantly diminished: Z score was -1.33 +/- 0.89 (P less than 0.001), while the BMD of lumbar spine was significantly augmented (Z score +1.95 +/- 1.17, P less than 0.001). A positive correlation was found between the Z scores for the BMD of the radius shaft and spine. The two patients with overt rickets had lower radius shaft BMD values and a lesser increment of BMD of the spine. The BMD deficit of cortical bone may be related to the lack of efficacy of the treatment and/or to an intrinsic defect of the bone on this disease. On the other hand, the augmented BMD of the lumbar spine might reflect the overabundance of partially mineralized osteoid. The determination of the BMD of the radius shaft by SPA was a sensitive method for detecting abnormalities of the bone mass in XLH patients under treatment without radiological signs of rickets.

Association of multiple nucleotide variations in the pituitary glutaminyl cyclase gene (QPCT) with low radial BMD in adult women

Correlation between 13 genetic variations of the glutaminyl-peptide cyclotransferase gene and adjusted aBMD was tested among 384 adult women. Among 13 variations with strong linkage disequilibrium, R54W showed a prominent association (p = 0.0003), which was more striking when examined among 309 elder subjects (> or =50 years; p = 0.0001). Contribution for postmenopausal bone loss was suggested.

INTRODUCTION

Alterations in homeostatic regulation of estrogen through the hypothalamus-pituitary-gonadal axis (HPG axis) importantly affect the pathogenesis of osteoporosis. Osteoporosis-susceptibility genes have been proposed in this hormonal axis, such as estrogen receptor genes and the gonadotropin-releasing hormone gene (GnRH). Here we report another example of genes: glutaminyl-peptide cyclotransferase gene (QPCT), an essential modifier of pituitary peptide hormones, including GnRH.

MATERIALS AND METHODS

Analyses of association of 13 single nucleotide polymorphisms (SNPs) at the QPCT locus with adjusted areal BMD (adj-aBMD) were carried out among 384 adult women. Linkage disequilibrium (LD) was analyzed by haplotype estimation and calculation of D' and r2. Multiple regression analysis was applied for evaluating the combined effects of the variations.

RESULTS AND CONCLUSIONS

LD analysis indicated strong linkage disequilibrium within the entire 30-kb region of the QPCT gene. Significant correlations were observed between the genotypes of the six SNPs and the radial adj-aBMD, among which R54W (nt + 160C>T) presented the most prominent association (p = 0.0003). Striking association was observed for these SNPs among the 309 subjects >50 years of age (R54W, p = 0.0001; -1095T>C, p = 0.0002; -1844C>T, p = 0.0002). Multiple regression analyses indicated that multiple SNPs in the gene might act in combination to determine the radial adj-aBMD. These results indicate that genetic variations in QPCT are the important factors affecting the BMD of adult women that contribute to susceptibility for osteoporosis. The data should provide new insight into the etiology of the disease and may suggest a new target to be considered during treatment.

Bone strength of caged layers as affected by dietary calcium and phosphorus concentrations, reconditioning, and ash content

1. The effects of preconditioning, dietary calcium and phosphorus concentrations, ash content, body weight, and bone geometry on the shear strength of the radius of caged layers were investigated. 2. Birds that did not lay for three or more weeks before the end of the production period had higher radius bone strengths than the birds producing eggs. 3. Shear breaking force increased with bone ash content. 4. The shear breaking force and stress of the radius were not affected by increasing dietary calcium and phosphorus during the last 8 weeks of production. 5. Freezing and thawing before testing had no effect on bone strength. 6. Body weight cannot be used to predict the breaking force of the radius of caged layers.

Dual energy X-ray absorptiometry of the calcaneus: comparison with other techniques to assess bone density and value in predicting risk of spine fracture

OBJECTIVE

The calcaneus has been proposed as an alternative site for assessment of bone mineral density (BMD) in women with osteoporosis. The objectives of this study were to evaluate the clinical usefulness of dual-energy X-ray absorptiometry (DXA) of the calcaneus for predicting spinal fracture and to compare the predictive value of assessment of BMD by DXA of the calcaneus, quantitative CT or DXA of the lumbar spine, and DXA of the most distal part of the radius.

SUBJECTS AND METHODS

The study group consisted of 399 healthy volunteer women (aged 19-81 years) and 27 women (aged 44-85 years) who had osteoporosis. They had DXA of the calcaneus, quantitative CT and DXA of the lumbar spine, and DXA of the most distal part of the radius. T-score analyses were used to compare decreases in BMD in postmenopausal women with decreases in premenopausal women, and to compare decreases in women with and without osteoporosis.

RESULTS

T-score analysis of age-related changes in BMD in the control subjects showed that densities in the calcaneus, the lumbar spine, and the most distal part of the radius decrease significantly with age in postmenopausal women. In women with osteoporosis (n = 27), BMDs in the calcaneus (DXA, p < .0002), L1-L3 (quantitative CT, p < .0001), L1-L4 (DXA, p < .0005), and the most distal part of the radius (DXA, p < .005) were significantly lower than those in healthy control subjects (n = 77). T-score analysis indicated that in women with osteoporosis, DXA of the calcaneus showed BMD losses greater than those shown by DXA of L1-L4 and the most distal part of the radius and similar to those shown by quantitative CT of L1-L3. Receiver-operating characteristic (ROC) analysis showed that findings on DXA of the calcaneus were as good a predictor of the risk of spinal fracture as findings on DXA of the lumbar spine and not as good as findings on quantitative CT of the lumbar spine.

CONCLUSION

The results suggest that DXA assessment of BMD in the calcaneus is not a useful adjunct to other measurements. However, it can be used to predict the risk of fracture when better measures, such as quantitative CT, are unavailable.

The relationship between body composition and bone mineral content: threshold effects in a racially and ethnically diverse group of men

We examined BMC and body composition in 1,209 black, Hispanic, and white men. Weight, BMI, waist circumference, and fat mass were associated with BMC only up to certain thresholds, whereas lean mass exhibited more consistent associations. The protective influence of increased weight appears to be driven by lean mass.

INTRODUCTION

Reduced body size is associated with decreased bone mass and increased fracture risk, but associations in men and racially/ethnically diverse populations remain understudied. We examined bone mineral content (BMC) at the hip, spine, and forearm as a function of body weight, body mass index (BMI), waist circumference, fat mass (FM), and nonbone lean mass (LM).

METHODS

The design was cross-sectional; 363 non-Hispanic black, 397 Hispanic, and 449 non-Hispanic white residents of greater Boston participated (N = 1,209, ages 30-79 y). BMC, LM, and FM were measured by DXA. Multiple linear regression was used to describe associations.

RESULTS

Weight, BMI, waist circumference, and FM were associated with BMC only up to certain thresholds. LM, by contrast, displayed strong and consistent associations; in multivariate models, femoral neck BMC exhibited a 13% increase per 10 kg cross-sectional increase in LM. In models controlling for LM, positive associations between BMC and other body composition measures were eliminated. Results did not vary by race/ethnicity.

CONCLUSIONS

The protective effect of increased body size in maintaining bone mass is likely due to the influence of lean tissue. These results suggest that maintenance of lean mass is the most promising strategy in maintaining bone health with advancing age.

Effect of parathyroidectomy on bone mineral density in hemodialysis patients with secondary hyperparathyroidism: possible usefulness of preoperative determination of parathyroid hormone level for prediction of bone regain

PURPOSE

To examine longitudinal changes of bone mineral density (BMD) after parathyroidectomy (PTx) in patients undergoing maintenance hemodialysis (HD) with severe secondary hyperparathyroidism (HPT) to determine which factor contributes most to bone changes.

METHODS

Fifteen Japanese HD patients who had been refractory to medical therapy were subject to PTx with autotransplantation. We measured BMD by dual energy X-ray absorptiometry (DXA) at the lumbar spine (L2 - 4 BMD) and the distal 1/3 region of the radius (1/3R BMD) at 1, 3, 6, 12, 24, and 36 months after PTx.

RESULTS

Baseline Z-score of BMD was markedly low at 1/3R (- 3.07) and slightly low at L2 - 4 (-0.59) in this group. A significant increase in L2 - 4 BMD was observed as early as one month after PTx, which was sustained afterwards. Annual percent changes in L2 - 4 and 1/3R BMD were + 15.6 % and + 6.4 %, respectively. The annual percent changes in BMD at both sites were positively associated with preoperative intact PTH levels (L2 - 4; r = 0.642, p = 0.010, 1/3R; r = 0.884, p < 0.001) and total alkaline phosphatase (ALP) levels (L2 - 4; r = 0.663, p = 0.007, 1/3R; r = 0.858, p < 0.001). Stepwise multiple regression analysis revealed that serum levels of intact PTH and ALP were the best predictors of both percentage and net changes in radial BMD with high determination coefficients (r 2 > 0.8).

CONCLUSION

Successful PTx following appropriate supplementation with vitamin D and calcium provides a marked increase in lumbar BMD and a modest increase in radial BMD in HD patients with secondary HPT. Preoperative levels of PTH and ALP are useful for predicting postoperative changes in bone mass.

Bone mineral density in male Baltic grey seal (Halichoerus grypus)

Bone mineral density (mg cm(-3)) was studied in male Baltic grey seals (4-23 years of age) by noninvasive computed tomography (pQCT). The material was grouped according to year of collection. Group A: 1850-1955, a period before the main introduction of organochlorines (OCs); Group B: 1965-1985, a period with very high OC contamination; and Group C: 1986-1997, a period with decreasing concentrations of OCs. The reproducibility of the measurements was good with a Coefficient of Variation (CV) ranging from 0.1% to 2.1%. Trabecular bone mineral density of the radius was significantly higher in specimens collected 1986-1997 than in those collected 1965-1985 (p < 0.05). Cortical bone mineral density of the mandible was significantly lower in specimens collected 1986-1997 compared with those collected 1850-1955 (p < 0.05). These results indicate different responses over time in trabecular and cortical bone. During the period of very high OC contamination (1965-1985), trabecular bone density was lowest, whereas cortical bone density was lowest in specimens collected 1985-1997, representing a period of fairly low OC contamination. The mechanisms behind these effects are not known. However, it can be assumed that OCs are involved. Information about residue levels of OCs in the studied individuals is lacking and, therefore, it was not possible to evaluate the impact of OCs in this respect.

Bone mineral density reference standards in adult baboons (Papio hamadryas) by sex and age

Osteoporosis is a progressive condition involving structural deterioration of bone tissue, leading to skeletal fragility and an increased susceptibility to fractures due to low bone mass and high rates of bone turnover. Areal bone mineral density (aBMD) serves as the most reliable predictor of susceptibility to osteoporotic fracture. The development of animal models, including Old World Monkeys, has been essential to studies of bone mineral density. These animals, including the baboon, exhibit many biological similarities with our own species relevant to the variation in age-related changes and pathology in bone that may make them an excellent model for studies of skeletal structure and maintenance in humans. The baboon has been shown to exhibit extensive biological similarities to humans regarding skeletal biology, but little is known about the range of normal variation in skeletal traits, such as bone mineral density, in this species. Our data, collected on baboons (Papio hamadryas) that are part of a large breeding colony at the Southwest Foundation for Biomedical Research and the Southwest National Primate Research Center (San Antonio, TX), involve 466 females and 210 males, ranging in age from 5.5 to 30 years. Student's t tests, bivariate correlations, and likelihood ratio tests show sex and age effects at all spinal sites. Age effects are minimal or absent in the forearm sites. This study is the first to characterize normal variation in aBMD in baboons, to assess the effect of age and sex on this variation, and to compare this variation to those data currently available from experimental control animals. As such, it provides much-needed reference standards that will allow researchers to evaluate the status of their animals in cross-sectional studies and more fully assess the meaning of aBMD changes in longitudinal studies.

Effects of long-term maternal intravenous magnesium sulfate therapy on neonatal calcium metabolism and bone mineral content

A prospective study was designed to determine whether calcium homeostasis and bone mineral content were affected adversely in preterm infants born to mothers receiving long-term antenatal therapy with magnesium sulfate. Preterm infants born to mothers receiving long-term antenatal therapy with magnesium sulfate and requiring prolonged bed rest for preterm labor were compared with infants of mothers not receiving magnesium sulfate but in whom prolonged bed rest was also required. Serum magnesium, calcium, phosphorus, osteocalcin, and parathyroid hormone were measured in infants at 0, 24, 48, and 72 h after delivery. Bone mineral content of the distal radius was measured 1 week postnatally and at term-equivalent postmenstrual age. Maternal serum mineral status indices obtained near delivery and bone indices were compared with those of their infants. The clinical characteristics and morbidities of the infants were similar between groups. We observed significantly greater serum concentrations of magnesium, phosphorus, and osteocalcin during the 72 h after delivery and a lower serum calcium concentration which normalized by 72 h in preterm infants whose mothers were treated with magnesium sulfate compared with infants whose mothers did not receive magnesium sulfate. Both groups, however, had similar radius bone mineral content measurements and anthropometric indices after delivery. These data suggest that although preterm infants born to mothers treated with magnesium sulfate have delayed clearance of magnesium and phosphorus, they have a normalization of serum calcium by 72 h after delivery and no significant differences in bone mineral content after delivery compared with infants whose mothers do not receive magnesium sulfate.

Mechanical properties and chemical composition of avian long bones

We have studied the mechanical behaviour of avian long bones as whole structures, by calculating mechanical parameters such as maximum load, stiffness, bending strength and flexural Young's modulus; bones were always tested in three-point bending. Furthermore composition in several chemical elements and amino acids related to collagen content was also analysed. Correlations were established between body mass, mechanical parameters and chemical contents. Both bending strength and Young's modulus were negatively correlated to body mass. Significant correlations were found between nitrogen content and both strength and Young's modulus, with negative slopes in both cases. Magnesium and phosphorus appear to be the most important inorganic elements to the understanding of the mechanical behaviour of avian long bones.