Regional and total skeletal measurements in the early postmenopause

Automated, calibration-free quantification of cortical bone porosity and geometry in postmenopausal osteoporosis from ultrashort echo time MRI and deep learning

BACKGROUND

Assessment of cortical bone porosity and geometry by imaging in vivo can provide useful information about bone quality that is independent of bone mineral density (BMD). Ultrashort echo time (UTE) MRI techniques of measuring cortical bone porosity and geometry have been extensively validated in preclinical studies and have recently been shown to detect impaired bone quality in vivo in patients with osteoporosis. However, these techniques rely on laborious image segmentation, which is clinically impractical. Additionally, UTE MRI porosity techniques typically require long scan times or external calibration samples and elaborate physics processing, which limit their translatability. To this end, the UTE MRI-derived Suppression Ratio has been proposed as a simple-to-calculate, reference-free biomarker of porosity which can be acquired in clinically feasible acquisition times.

PURPOSE

To explore whether a deep learning method can automate cortical bone segmentation and the corresponding analysis of cortical bone imaging biomarkers, and to investigate the Suppression Ratio as a fast, simple, and reference-free biomarker of cortical bone porosity.

METHODS

In this retrospective study, a deep learning 2D U-Net was trained to segment the tibial cortex from 48 individual image sets comprised of 46 slices each, corresponding to 2208 training slices. Network performance was validated through an external test dataset comprised of 28 scans from 3 groups: (1) 10 healthy, young participants, (2) 9 postmenopausal, non-osteoporotic women, and (3) 9 postmenopausal, osteoporotic women. The accuracy of automated porosity and geometry quantifications were assessed with the coefficient of determination and the intraclass correlation coefficient (ICC). Furthermore, automated MRI biomarkers were compared between groups and to dual energy X-ray absorptiometry (DXA)- and peripheral quantitative CT (pQCT)-derived BMD. Additionally, the Suppression Ratio was compared to UTE porosity techniques based on calibration samples.

RESULTS

The deep learning model provided accurate labeling (Dice score 0.93, intersection-over-union 0.88) and similar results to manual segmentation in quantifying cortical porosity (R2 ≥ 0.97, ICC ≥ 0.98) and geometry (R2 ≥ 0.82, ICC ≥ 0.75) parameters in vivo. Furthermore, the Suppression Ratio was validated compared to established porosity protocols (R2 ≥ 0.78). Automated parameters detected age- and osteoporosis-related impairments in cortical bone porosity (P ≤ .002) and geometry (P values ranging from <0.001 to 0.08). Finally, automated porosity markers showed strong, inverse Pearson's correlations with BMD measured by pQCT (|R| ≥ 0.88) and DXA (|R| ≥ 0.76) in postmenopausal women, confirming that lower mineral density corresponds to greater porosity.

CONCLUSION

This study demonstrated feasibility of a simple, automated, and ionizing-radiation-free protocol for quantifying cortical bone porosity and geometry in vivo from UTE MRI and deep learning.

Radius bone strength in bending, compression, and falling and its correlation with clinical densitometry at multiple sites

This study comprehensively analyzes the ability of site-specific and nonsite-specific clinical densitometric techniques for predicting mechanical strength of the distal radius in different loading configurations. DXA of the distal forearm, spine, femur, and total body and peripheral quantitative computed tomography (pQCT) measurements of the distal radius (4, 20, and 33%) were obtained in situ (with soft tissues) in 129 cadavers, aged 80.16 +/- 9.8 years. Spinal QCT and calcaneal quantitative ultrasound (QUS) were performed ex situ in degassed specimens. The left radius was tested in three-point bending and axial compression, and the right forearm was tested in a fall configuration, respectively. Correlation coefficients with radius DXA were r = 0.89, 0.84, and 0.70 for failure in three-point bending, axial compression, and the fall simulation, respectively. The correlation with pQCT (r = 0.75 for multiple regression models with the fall) was not significantly higher than for DXA. Nonsite-specific measurements and calcaneal QUS displayed significantly (p < 0.01) lower correlation coefficients, and QUS did only contribute to the prediction of axial failure stress but not of failure load. We conclude that a combination of pQCT parameters involves only marginal improvement in predicting mechanical strength of the distal radius, nonsite-specific measurements are less accurate for this purpose, and QUS adds only little independent information to site-specific bone mass. Therefore, the noninvasive diagnosis of loss of strength at the distal radius should rely on site-specific measurements with DXA or pQCT and may be the earliest chance to detect individuals at risk of osteoporotic fracture.

Skeletal effects of menstrual disturbances in athletes

This article reviews the skeletal effects and clinical implications of menstrual disturbances in active women. At the lumbar spine, menstrual disturbances are associated with premature bone loss or failure to reach peak bone mass, while appendicular sites are less affected. This suggests that trabecular bone is more sensitive to hormonal stimuli and less responsive to mechanical loading than cortical bone. Although the mechanisms responsible for the detrimental effects of menstrual disturbances are likely to be multifactorial, low circulating levels of oestrogen are thought to be the main cause. The clinical significance of menstrual disturbances depends upon a number of factors, including type of sport, genetic background, body composition and calcium intake. Not all athletes who present with menstrual disturbances will develop osteopenia. Nevertheless, the risk of stress fracture does seem to be increased in athletes with menstrual disturbances and with lower bone density. Whether athletes with menstrual disturbances are at a greater risk for osteoporosis in later life is not yet known. Bone loss can be at least partially reversed, especially with the spontaneous resumption of menses. This may serve to offset any previous increased risk of osteoporosis. Furthermore, other factors, apart from low bone mass, act to determine the likelihood of osteoporotic fractures. Therefore, the clinical significance of menstrual disturbances associated with exercise participation needs to be established for each individual athlete. Bone densitometry may guide the clinician in this respect and assist in the formulation of appropriate management strategies.

The impact of bone loss in women with endometriosis

Low peak adult bone mass in a premenopausal woman puts her at increased risk for osteoporosis postmenopausally. Episodes of hypo-estrogenism premenopausally are associated with loss of bone density. This is seen with gonadotropin-releasing hormone agonist therapy for endometriosis, and thus prolonged or repeated courses of such treatment may increase the future risk of osteoporosis. Danazol and related compounds do not result in any bone loss but may have certain metabolic disadvantages.

Prevention of early postmenopausal bone loss using low doses of conjugated estrogens and the non-hormonal, bone-active drug ipriflavone

Hormone replacement therapy is the optimal therapeutic choice for postmenopausal syndrome. While low doses of estrogens (0.3 mg/day of conjugated estrogens) can counteract neurovegetative menopausal symptoms, higher doses (0.625 mg/day of conjugated estrogens) are required to prevent bone loss in postmenopausal women. Experimental and clinical studies have shown that ipriflavone, a non-hormonal isoflavone derivative, is effective in the prevention and treatment of postmenopausal osteoporosis. The aim of the present investigation was to evaluate the efficacy and tolerability of ipriflavone and very low doses of equine conjugated estrogens on bone loss in early postmenopausal women. Eighty-three healthy postmenopausal women (50.3 +/- 0.7 years) were enrolled for this 1-year multicenter study. All subjects were randomly allocated to receive: double placebo (n = 24; group A), placebo plus conjugated equine estrogens 0.30 mg/day (n = 31; group B) or conjugated equine estrogens 0.30 mg/day plus oral ipriflavone 200 mg tris in die at meals (n = 28; group C), according to a double-masked design. Among women who completed the treatment period (valid completers), those of group A showed a progressive decrease in forearm bone density (FBD; measured by dual photon absorptiometry) that reached 1.7% after 12 months. The women in group B maintained their FBD in the first 6 months of treatment but, at the end of the study, showed a bone loss of 1.4% compared with basal values. By contrast, women in group C showed a significant increase in FBD after 1 year of treatment (+5.6%; p < 0.01). Both valid completers and intention to treat analyses revealed a significant difference (p < 0.05) between group A and group C over the study period. None of the treatments produced significant changes of biochemical markers of bone turnover, while hot flushes and other climacteric symptoms were significantly reduced after the sixth month of treatment in women receiving estrogens. Adverse events were generally mild, and did not differ among the groups. The results of this study suggest that low doses of estrogens combined with ipriflavone could represent a new therapeutic approach to the treatment of the postmenopausal syndrome.

Influence of the menopausal age on the severity of osteoporosis in women with vertebral fractures

To assess the effect of age at the onset of menopause over the skeleton we have determined the age and cause of menopause and bone mineral density (BMD), by dual and single photon absorptiometry of the lumbar spine, the proximal femur and the radius shaft on 1050 osteoporotic women (suffering with at least one atraumatic vertebral fracture). The mean +/- 1 S.D. menopausal age was 47.1 +/- 7.6 years. The onset of menopause occurred prior to age 45 in 22% (premature), after age 52 in 9% (late), and between 45 and 52 years of age in 69% (normal menopausal age). When the osteoporotic women were categorized into three groups according to the age of menopause, those osteoporotic with premature menopause had a significantly greater frequency of hip fractures, a significantly lower age, weight and BMD over the spine, proximal femur and radius shaft compared with those of normal menopausal age. In turn, patients with late menopause had a significantly increased weight and BMD over the spine. These findings indicate that among patients with vertebral osteoporosis those women with premature menopause had a more severe bone loss and a significantly greater frequency of hip fractures.

Bone mineral density in young women with long-standing amenorrhea: limited effect of hormone replacement therapy with ethinylestradiol and desogestrel

To assess bone mineral density (BMD) at different skeletal sites in women with hypothalamic or ovarian amenorrhea and the effect of estrogen-gestagen substitution on BMD we compared BMD of 21 amenorrheic patients with hypothalamic or ovarian amenorrhea with that of a control population of 123 healthy women. All amenorrheic patients were recruited from the outpatient clinic of the Division of Gynecological Endocrinology at the University of Berne, a public University Hospital. One hundred and twenty-three healthy, regularly menstruating women recruited in the Berne area served as a control group. BMD was measured using dual-energy X-ray absorptiometry (DXA). At each site where it was measured, mean BMD was lower in the amenorrheic group than in the control group. Compared with the control group, average BMD in the amenorrheic group was 85% at lumbar spine (p < 0.0001), 92% at femoral neck (p < 0.02), 90% at Ward's triangle (p < 0.03), 92% at tibial diaphysis (p < 0.0001) and 92% at tibial epiphysis (p < 0.03). Fifteen amenorrheic women received estrogen-gestagen replacement therapy (0.03 mg ethinylestradiol and 0.15 mg desogestrel daily for 21 days per month), bone densitometry being repeated within 12-24 months. An annual increase in BMD of 0.2% to 2.9% was noted at all measured sites, the level of significance being reached at the lumbar spine (p < 0.0012) and Ward's triangle (p < 0.033). In conclusion BMD is lower in amenorrheic young women than in a population of normally menstruating, age-matched women in both mainly trabecular (lumbar spine, Ward's triangle, tibial epiphysis) and mainly cortical bone (femoral neck, tibial diaphysis).(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary evaluation of a new ultrasound bone densitometer

A new ultrasound bone densitometer has been developed that measures ultrasonic properties of the os calcis, namely, the speed of sound (SOS), broadband ultrasound attenuation (BUA), and a proprietary factor derived from SOS and BUA, termed "stiffness." Short-term precision of ultrasound measurements was 1.4% for BUA, 0.2% for SOS, and 1.5% for stiffness in healthy women, and 1.1% for BUA, 0.1% for SOS, and 1.5% for stiffness in osteopenic women. One hundred seven women underwent measurements by ultrasound, together with dual energy X-ray absorptiometry (DXA) bone mineral density (BMD) measurements of the lumbar spine and proximal femur. Correlations between SOS, BUA, and stiffness measurements and DXA BMD measurements were all highly significant (P < 0.001) with r values varying from 0.54 to 0.67. BUA, SOS, and stiffness measurements were all significantly different between normal and osteopenic women even after adjusting for age, height, and weight (P < 0.05, P < 0.001, and P < 0.01, respectively). These results demonstrate that this ultrasound system measures ultrasonic properties of the os calcis with good precision, the measurements correlate moderately well with DXA BMD measurements and they can differentiate between normals and those with osteopenia.

Bone changes in postmenopausal Spanish women

Total body bone mass (TBBM), axial bone mass (trunk = chest and spine), and peripheral bone mass (arms and legs) were determined in 258 normal, slow bone mass loser, postmenopausal women, as determined by previous biochemical studies, in order to study the degree of bone mass reduction due to menopause. The subjects of this study were divided into 5-year groups on a year-since-menopause basis. The first group corresponded to 1-5 years since menopause, and the last group to 25 years or over since menopause. An important and significant reduction in trunk bone mass (-12.3%, P < 0.001) and TBBD (-5.8%, P < 0.002), without changes in head, arms, and legs was observed in the first 5-year group. In the next 5-year group, a significant reduction was observed in all body areas, but at a higher rate in the peripheral skeleton (-9% in arms and -7.3% in legs). A slow down in bone mass loss was observed in the period between 10 and 25 years since menopause. These values became significant again after 25 years since menopause at the axial (-28.9%, P < 0.001) and TBBD (-20.3%, P < 0.05) level. Aside from providing percentages of bone mass reduction with respect to age and time since menopause, these data also indicate that measurements of specific body areas may not be extrapolated to others due to different loss in different body areas, and that there is a marked bone loss rate in the axial skeleton in the first 5 years since menopause.

Body composition and bone mass in post-menopausal women

OBJECTIVE

We aimed to assess total body composition and to study the interrelationships between fat and lean tissue mass with total and regional bone mass in healthy British post-menopausal women.

DESIGN AND PATIENTS

Total body composition and regional bone mass were measured in 97 healthy post-menopausal women recruited from the general community. The mean age was 57.9 years, range 49-65.

MEASUREMENTS

Total body composition (fat, lean tissue and bone mineral) and regional bone density in the lumbar spine and femur were measured by dual energy X-ray absorptiometry on a Lunar DPX.

RESULTS

Significant negative correlations with age were found for total body bone mineral density (r = -0.200, P = 0.049), and lumbar spine bone mineral density (r = -0.28, P = 0.006); the calculated rate of bone loss from these two sites was 0.33 and 0.7% per annum respectively. Fat tissue mass showed a positive correlation with age (r = 0.22, P = 0.03). High correlations were observed between total body and regional bone mineral density (r = 0.755-0.829, P < 0.001). After adjustment for age and lean mass, statistically significant correlations were seen between fat tissue mass and all bone mass measurements (P < 0.01-0.001), the strongest correlations being found for total body bone mineral content and density (r = 0.477 and 0.488 respectively). Lean tissue mass showed a strong correlation with total body bone mineral content (r = 0.580, P < 0.001), after adjustment for age and fat mass; it was less strongly correlated with other bone mass measurements than fat mass, showing only weak correlations with total body, trochanteric and lumbar spine bone mineral density (r = 0.228-0.246, P < 0.05). Age-adjusted body weight showed stronger correlations with total and regional bone mass than did either body mass index or height.

CONCLUSIONS

Both fat and lean tissue mass are related to total and regional bone mass in post-menopausal women, the relationship being strongest for fat mass. Body weight shows stronger correlations with bone mass than either height or body mass index. In view of the direction and magnitude of changes in fat, lean tissue and bone mineral after the menopause, adiposity and muscularity are more likely to be determinants of peak bone mass than of the rate of post-menopausal bone loss.

Ipriflavone and low doses of estrogens in the prevention of bone mineral loss in climacterium

Estrogen replacement therapy can counteract all postmenopausal symptoms. While low estrogen doses (0.15-0.30 mg of conjugated estrogens/day) can counteract neurovegetative and psychological symptoms, higher estrogen doses (at least 0.625 mg of conjugated estrogens/day) are required to prevent bone mineral loss in postmenopausal women. However, if contra-indications to high estrogen doses exist, drugs other than estrogens can represent a suitable treatment for postmenopausal osteoporosis both alone or in combination with low estrogen doses. Experimental and clinical data have shown that ipriflavone is effective in the treatment of established postmenopausal osteoporosis. With the purpose of evaluating whether ipriflavone is able to enhance estrogen activity on bone metabolism, 133 postmenopausal women were randomly submitted to the treatment with: (1) placebo; (2) 0.15 mg/day of conjugated estrogens; (3) 0.30 mg/day of conjugated estrogens; (4) 0.15 mg/day of conjugated estrogens plus 600 mg/day of ipriflavone; (5) 0.30 mg/day of conjugated estrogens plus 600 mg/day of ipriflavone. One g/day of calcium supplementation was given to all women. In all subjects bone mineral density was measured before and after 6 and 12 months of treatment at the distal radius by dual-photon absorptiometry. A moderate decrease of bone mineral density was evidenced in women submitted to placebo or to estrogen therapy alone. By contrast, an increase of BMD was measured after 12 months of treatment in the women treated with 0.15 (not significant) or 0.30 mg/day (P < 0.01) of conjugated estrogens associated with ipriflavone. Both dosages of conjugated estrogens were able to induce a significant reduction of neurovegetative symptoms. The increase of bone density obtained with the combination of conjugated estrogens with ipriflavone demonstrates that this combination improves the effects of low estrogen doses on bone mass representing a satisfactory approach in the prevention and treatment of all symptoms related to the climacteric syndrome.

The effect of sex steroids on the skeleton in premenopausal women

Whereas peak bone mass is genetically determined, the skeletal growth, maturation, and maintenance required to reach this peak may be influenced by physical activity, ovarian function, and nutrition. Estrogen deficiency at menopause leads to increased skeletal remodeling and loss of bone mass, which can result in osteoporotic fractures. Entering menopause with low bone mass is a risk factor itself, because bone mass predicts future risk of fracture. The administration of exogenous steroids can reverse the setting of the "mechanostat" to lower levels after ovarian dysfunction, although it is unclear whether oral contraceptives can modify bone mass in the ovulatory premenopausal woman. Our recent data suggest that the use of steroidal hormones to treat menstrual irregularity (presumably relative to ovarian dysfunction), as opposed to fertility control, is more likely to positively affect bone mass. It is even less clear whether hyperestrogenic states (e.g., pregnancy) affect the skeleton. Recent evidence from bone mass changes that occur in women with ovulatory cycles and inadequate luteal phase function suggests that progestins may also influence skeletal metabolism.

The long-term risks and benefits of hormone replacement therapy

There is increasing awareness that the long-term consequences of ovarian failure can be prevented or reduced with appropriate hormone replacement therapy (HRT). After the menopause, there is a rapid loss of trabecular bone resulting in a one in two lifetime risk of osteoporotic fracture. HRT prevents this bone loss and decreases the incidence of fracture. A minimum of 5 years treatment is recommended for significant benefit. Epidemiological evidence is accumulating that post-menopausal oestrogen therapy reduces the risk of cardiovascular disease and stroke by between 30 and 70% even in the presence of established risk factors. Given the prevalence of cardiovascular disease, this is likely to be one of the principle benefits of HRT in the next decade. Concerns about the long-term safety of HRT have focused on endometrial and breast cancer. The increase in risk of endometrial cancer associated with oestrogen only therapy is abolished with the sequential addition of a progestogen for 10-12 days each cycle. The possible effect of HRT on breast cancer risk has to be considered against the background of a one in 12 lifetime risk of developing this disease. The epidemiological studies investigating this relationship are reviewed in this paper. There is a broad consensus that 5-6 years duration of HRT does not increase breast cancer risk. Longer durations of therapy (10-15 years) have been reported to increase this risk although not all the data are in agreement. Other factors, such as family history and benign breast disease, may also influence the risk of breast cancer. The potential benefits of HRT on mortality and morbidity are enormous. Against this is a possible small increase in breast cancer risk with long-term usage. Greater awareness of the long term consequences of the menopause and the potential benefits of HRT should be encouraged so that women can make informed decisions about their need for HRT.

Effects of transdermal versus oral hormone replacement therapy on bone density in spine and proximal femur in postmenopausal women

66 early postmenopausal women were randomised to 28-day cycles of either transdermal hormone replacement therapy--continuous oestradiol 17-beta 0.05 mg daily, with norethisterone acetate 0.25 mg daily for 14 of each 28 days--or oral therapy--continuous conjugated equine oestrogens 0.625 mg daily, with dl-norgestrel 0.15 mg daily for 12 of each 28 days. An untreated reference group of 30 women were studied concurrently. Bone density was measured in the lumbar spine and proximal femur by dual photon absorptiometry at 6-month intervals for 18 months. Skeletal turnover was assessed by serum measurements of calcium, phosphate, and alkaline phosphatase, and by urine estimations of hydroxyproline/creatinine and calcium/creatinine excretion. In both treatment groups by comparison with the untreated groups by comparison with the untreated group, bone density increased in the vertebrae and proximal femur and biochemical measurements indicated a significant reduction in bone turnover.

Pathogenesis, prevention, and treatment of osteoporosis

Half of women who develop osteoporosis will sustain some form of osteoporotic fracture. Fracture incidence is directly related to bone density, which is determined by peak adult bone mass and the amount of postmenopausal bone loss. Peak adult bone mass is, to a large extent, genetically determined, but hormonal factors (time since menopause, number of pregnancies, and previous oral contraceptive use) are the prime determinants of bone density after menopause. Time elapsed since menopause, rather than chronological age, determines skeletal composition; oral contraceptive use and parity appear to have a positive effect on the skeleton. Nonhormonal factors such as body weight and some forms of weight-bearing exercise appear to correlate with bone density at certain skeletal sites. Hormone replacement in the early postmenopausal period is the most effective means of preventing osteoporosis and can have a major impact on the incidence of subsequent fracture. Calcitonin may be used as an alternative when hormonal therapy is contraindicated. Established osteoporosis is difficult to treat because bone density has fallen below the fracture threshold and trabecular elements may have been lost. Antiresorptive agents can be used to prevent further bone loss, and stimulation of new bone formation by use of anabolic steroids or fluoride may increase the overall amount of bone.

Determinants of bone density in normal women: risk factors for future osteoporosis?

Postmenopausal osteoporosis is an important public health problem in developed countries. Preventive treatment might effect a large reduction in the incidence, but this needs to be applied selectively to those women at increased risk. Loss of bone density results in an increased risk of fractures in the classical sites of vertebrae and proximal femur. A cross sectional study of bone density measurements was carried out in these sites in British women with a modern, precise densitometric technique. Possible predictors and risk factors for bone density were assessed in these women. Bone density was measured by dual photon absorptiometry in 284 apparently healthy women volunteers aged 21 to 68. The values obtained were similar to those obtained from equivalent studies performed in women in the United States. Peak adult bone density had been attained soon after the end of linear skeletal growth. Thereafter there was some decline with age in the proximal femur, but the major fall in bone density in all sites was related to the menopause. Other factors decreasing bone density, and hence increasing risk for osteoporosis, such as low body weight, alcohol and cigarette consumption, nulliparity, lack of previous use of oral contraceptives, and lack of regular exercise, seemed to be important. None, however, could predict satisfactorily women at future risk for osteoporosis. Direct measurements of bone density in the clinically relevant sites are necessary to determine which women should received preventive treatment for postmenopausal osteoporosis. This would help make such treatment more cost effective.

The relation between forearm and vertebral mineral density and fractures in postmenopausal women

Vertebral and forearm mineral density (VMD and FMD, respectively) were determined in 124 postmenopausal women with no crushed vertebrae or peripheral fractures, 51 who had sustained peripheral fractures only since the menopause, 62 with vertebral compression(s) only and 75 with both types of fracture. There was a very significant correlation between the two measurements in the whole set. The scatter could not be accounted for by methodological error but was partly accounted for by body weight, since VMD was related to body weight and FMD was not. Whatever criterion was used for the diagnosis of osteoporosis (whether fracture or density) the percentage of misclassified cases was very similar by the two methods. However, VMD was relatively more reduced than FMD in vertebral fracture cases and FMD was marginally more reduced than VMD in peripheral fracture cases. There is little to choose between vertebral and forearm density in the diagnosis of osteoporosis but vertebral densitometry is slightly superior to forearm densitometry in describing the severity of osteoporosis in vertebral fracture patients.

Dietary intake of calcium and postmenopausal bone loss

The use of calcium supplements to prevent postmenopausal bone loss and hence osteoporosis is widespread, but the evidence for their efficacy, either alone or in combination with other treatments, is contradictory. Skeletal measurements and dietary intake of calcium were determined in 59 healthy postmenopausal women, most of whom were within five years of the menopause. No correlation was found between current intake of calcium and either total calcium in the body or the density of trabecular or cortical bone in the forearm or vertebral trabecular bone. Dietary intake of calcium did not influence the rate of postmenopausal bone loss in the 54 women who completed 12 months of active or placebo treatment. Even when extremes of calcium intake were examined no difference was found in bone measurements between the women with the highest and lowest intakes. The results of this study suggest that the bone density of women in the early menopause is not influenced by current dietary intake of calcium.

Bone mineral content in normal UK subjects

Bone mineral content in the lumbar vertebrae and in the shaft of the left radius has been measured in 129 normal British subjects using quantitative computed tomography and single-photon absorptiometry. Significant negative correlations between bone mineral content and age were found at both sites in males and females (p less than 0.001 in all cases). When expressed in g/cm the bone mineral content in the radial shaft showed significant positive correlations with body height and weight in both sexes, but after correction for bone size only a weak correlation with body height in males was found. Spinal trabecular bone mineral content showed no significant correlations with body height or weight in either sex. Comparison of the values obtained with normal data from centres in the USA revealed lower mean values for both radial and spinal bone mineral content in the British subjects. These differences emphasize the importance of using locally derived normal data for comparison with values obtained from patients.