Long term lead metabolism in the human body has never been fully understood due to the lack of human data in this area. The technological improvement of bone lead measurement systems has made bone lead data of substantial populations available. In this study, a set of X-ray fluorescence bone lead data was used to test Leggett's lead metabolism model (R. W. Leggett, Environ. Health Perspect., 1993a, 101, 598-616), especially the model of metabolism in bone. The data set includes the bone lead concentration of 539 occupationally exposed workers, of whom 327 were measured twice in five years. The bone lead concentrations of both cortical bone (tibia) and trabecular bone (calcaneus) were obtained by Cd-109 gamma-ray induced XRF measurement. The histories of blood lead concentration for these workers were used to regulate the input file of the model. The results show that the bone lead concentrations predicted by Leggett's model greatly underestimate the measured values, especially for older workers. This data set was then organized into five age groups. A new simplified model was applied to estimate the lead transfer rates between blood and lead compartments for these age groups. The original transfer rates and the new transfer rates are compared, and the differences are discussed. When the transfer rates derived from measured bone lead data were put into the input file of the model to replace the existing parameters, the predicted values were much closer to the measured values for both cortical bone and trabecular bone.

This paper describes a new metabolic model for lead in humans and a numerical method to solve the differential equations governing the transfer of lead between body compartments. The model includes 3 compartments-cortical bone, trabecular bone and blood-and accounts for absorption from external sources and release through excreta. Estimation of the lead kinetics parameters was performed using the grid search method. Grid search is a simple procedure that allows the fit of an arbitrary function to data. When applied to data from occupationally exposed populations, the method demonstrated the exposure dependence of the rate of lead uptake and release by the compartments in the model. The results confirm and refine previous observations of the significant decrease of the transfer rate of lead from cortical bone to blood with increasing exposure, as expressed by half-lives of (in years): 6.5 +/- 0.7, 13.6 +/- 1.0 and 47.5 +/- 2.3, in subgroups of low, intermediate and high long-term lead exposure. A similar trend was observed for the transfer rate from trabecular bone, which could be statistically supported for the first time. Reduction by a factor of 7 to 10 in the default values assigned to the fractional removal of lead from cortical bone to plasma in existing metabolic models was also predicted. These results can be used in the review of current metabolic models for lead, which are still based on the assumption of a constant rate of lead removal from bone, independently of the level of exposure.

Objective: To investigate the relationships between bone mineral density (BMD) in the hip, spine, distal femur and proximal tibia and minimum joint space width (mJSW) in the knees of healthy women.Methods: Women 22-68 years old without a history of knee pain, bone or joint disease or injury underwent a single, fixed-flexion knee X-ray. Radiographs were graded according to the Kellgren-Lawrence scale and analyzed for mJSW using a computer algorithm. Dual X-ray absorptiometry scans of the spine, hip, distal femur and proximal tibia were also acquired for each participant. Femur and tibia scans were acquired and analyzed using a modified version of the lumbar spine software.Results: Forty-five females, mean [standard deviation (SD)] age and body mass index (BMI) of 40.1 (13.9) years and 24.6 (4.5) kg/m(2), respectively, participated. The mean (SD) mJSW was 4.64 (0.68) mm. Linear regression analyses controlling for age and BMI revealed that BMD in the femoral trochanter and the central two regions of the tibia (T2 and T3) was significantly related to mJSW in the knee. A backwards regression analysis performed to determine which region of interest is most significantly related to mJSW revealed that femoral trochanter BMD (beta-value = 0.416) is the most significant.Conclusions: In contrast to the suggestion that BMD is negatively correlated with mJSW in the knees of osteoarthritic individuals, these results suggest that increasing BMD in the femoral trochanter and tibia is significantly associated with increasing mJSW in healthy females. Further investigation of this relationship is warranted. (c) 2005 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

In 1994, 207 women participated in a study designed to examine the effects of occupational exposure and various lifestyle factors on bone and blood lead levels. In vivo measurements of Pb concentrations in tibia were performed by X-ray fluorescence. All 108 former smelter employees and 99 referents provided blood samples and answered a questionnaire on lifestyle characteristics and the relevant medical history. Lead concentrations in tibia and blood were significantly higher in the exposed group. The difference in mean bone Pb concentrations of the two groups is markedly greater than the difference in the mean blood Pb concentrations, supporting the view that bone Pb measurements are a more reliable determinant of Pb body burden. Chronic exposure did not result in any statistically significant differences in adverse pregnancy outcomes. A significantly lower age at the onset of menopause in occupationally exposed women may suggest that Pb causes adverse changes in the pattern of estrus and menses. The exposed women had lower bone Pb concentrations than those found in most studies on predominantly male workers. Blood Pb concentrations remain increased in women long after the cessation of occupational exposure, reflecting the importance of the endogenous exposure. The endogenous exposure relation found for postmenopausal exposed women is consistent with data on male smelter workers, whereas the relation found for premenopausal women is significantly lower. This suggests that sex plays an important role in the metabolism of lead, and current models of exposure extrapolated from male data may be inappropriate for use on women.

Objective: To estimate the prevalence of bone and soft tissue abnormalities in asymptomatic knees using peripheral magnetic resonance imaging (pMRI) and to examine the relationship between these abnormalities and Kellgren-Lawrence (K-L) graded X-rays.Method. Volunteers (20-68 years) with no history of knee pain, injury or bone or joint disease were recruited. Individuals underwent a single MRI scan and radiograph of their non-dominant knee. pMR images were acquired in sagittal plane using a 3-D gradient-echo protocol. Two radiologists graded the presence and severity of cartilage degeneration, osteophytosis, meniscal and ligamentous abnormalities, bone marrow edema and subchondral cysts. X-rays were acquired using a fixed-flexion technique and graded using the K-L scale.Results: Forty-four individuals, mean age (SD) 41.1 (14.2) years, participated. K-L grading of X-rays revealed 29 individuals were grade 0, 12 were grade 1 and 3 were grade 2. Five individuals showed evidence of cartilage lesions, the femoral trochlea, medial femur and patella being those regions most commonly affected. Twelve individuals (27.3%) showed evidence of osteophytosis, nine of whom did not show evidence on X-ray. Forty-three individuals showed evidence of at least one meniscal abnormality while 27 individuals (61.4%) had abnormalities in at least three of the four regions of the knee.Conclusion: Our results suggest that osteophytes may be more prevalent in this population than radiographic data suggests due to the limitations of two-dimensional imaging. Meniscal degeneration or tears, a risk factor for knee osteoarthritis, are highly prevalent in asymptomatic individuals with the medial anterior and posterior horns being the most commonly affected regions. (c) 2004 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

1079 Exercise associated muscle induced bone strain has potential osteogenic effects that may increase skeletal density, bone cross-sectional area and structural strength. Whether the effects of exercise and the muscle-bone relation are similar in weight bearing and non-weight bearing bones remains to be determined. PURPOSE: This study compared bone density, as well as bone and muscle cross-sectional areas of 13 adolescent male cross-country skiers competing at the Provincial and National levels with published age and maturity matched normative data (ND) on healthy non-athletic males. METHODS: Skiers were 17.3 +/− 1.1 years old, 177.4 +/−4.4 cm tall, 70.2 +/− 8.25 kg, 12.4+/−4.3% body fat, and Tanner Stage 4.8 +/−0.6. Total bone mineral content (BMCTOT), and total (BMDTOT) bone mineral density, cortical thickness and area (CSAcort), muscle cross-sectional area (mCSA) and the CSAcort/mCSA ratio were measured at the 66 % length of the proximal tibia (PT) using peripheral quantitative computed tomography (pQCT 2000, Stratec, Pforzheim, Germany). BMCTOT, CSAcort TOT and mCSA were also measured at the proximal radius (PR-66% length). RESULTS: PR BMCTOT of the skiers was not significantly different (98.99 +/− 18.87mg/mm) than controls (94 +/− 20mg/mm). Likewise, PT CSAcort, mCSA, as well as the CSAcort/mCSA ratios were similar between skiers and controls. Cortical thickness and BMDTOT at the PT were significantly higher in skiers (5.423+/−0.254mm p = 0.000; 649.3 +/− 65.6mg/cm3 p = 0.0064) than controls (3.909+/−0.467mm; 574.1+/−56.5mg/cm3). A difference was seen in the CSAcort/mCSA ratio between PR (0.022 +/− 0.004) and PT (0.048 +/− 0.005) suggesting differences in muscle-bone relations between load bearing and non-load bearing limbs in adolescent male cross-country skiers. CONCLUSION: Cross-country skiers had increased cortical thickness and BMDTOT at the PT compared to ND and a higher cortical bone/muscle area ratio at the PT compared to the PR, suggesting regional variability in the muscle-bone relation. Supported in part by Stratec, Pforzheim, Germany.

The need for in vivo bone strontium assessment arises because strontium may exert a number of effects on bone, which may be either beneficial or toxic. Measurements discussed here are noninvasive, no sample is taken, nor is there discomfort to patients. The developed source excited x-ray fluorescence system employs a 109Cd source to excite the strontium K x rays, with the source and detector in approximately 90 degree geometry relative to the sample position. The factors affecting the accuracy and minimal detectable limit for bone strontium in vivo measurements are discussed. A system calibration revealed a minimum detectible limit of approximately 0.25 mg Sr/g Ca, which is sufficient for the monitoring of strontium levels in healthy subjects and patients with elevated bone strontium concentrations. Preliminary in vivo measurements in ten healthy subjects at two bone sites (phalanx and tibia) indicated that this system can be applied for cumulative bone strontium estimation while delivering a low effective dose of 80 nSv during the measurement time. Future work will involve attempts to enhance system precision with alternative fluorescing sources and further optimization of the detection system.

Twenty-one of 46 postmenopausal women were assigned to a home-based exercise program consisting of 60 min of exercise, 3 d/wk. The 25 nonexercisers continued usual daily activities. Each woman had at least one prevalent vertebral fracture and suffered from osteoporosis as defined by the application of WHO criteria to lumbar spine bone mineral density. Vertebral heights were measured using bone densitometry at baseline and 12 mo later. Vertebrae T9 to L4 were all identified for each of the 46 subjects in both the baseline and end-of-study lateral scans. The change in mean vertebral height over the course of the study was -0.3 min anteriorly, -0.7 min at the mid-location, and -0.4 min posteriorly for the nonexercisers. For the exercisers, the corresponding changes were +0.1 min anteriorly, -0.3 min at the mid-location, and +0.2 min posteriorly. The benefit of exercise in preserving vertebral morphometry in patients with osteoporosis deserves further investigation.

The purpose of this cross-sectional case-control study was to determine whether indices of bone structure at the 4% site of the radius discriminate women who have sustained a recent low-energy fracture of the contralateral distal radius (n = 21) from women with similar bone density and no history of fracture (n = 21). Images of the distal forearm were acquired using peripheral quantitative computed tomography (pQCT) and were analyzed using in-house-developed software to determine indices of trabecular bone structure (average hole size [H(A)], maximum hole size, and connectivity index). The same images were analyzed using commercial software to determine bone density, mass, geometry, and torsional strength. The fracture group had significantly larger H(A) (p = 0.03). No other bone variable differed between groups. Individual H(A) values were compared to the mean value for young adult women (n = 42). The odds ratio (95% confidence interval) associated with an H(A) >2 SDs above the young adult mean was 5.4 (1.2-24.3). Thus, estimation of in vivo trabecular bone porosity by measuring the average diameter of the pQCT-imaged marrow spaces in the ultradistal radius identifies individuals with low bone mass most at risk for osteoporotic fracture.