PubMed · 7444031
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H Ammerich, R Golabek, A Wackenheim. 1980. [Tomodensitometry in exploring the orbit].. https://pubmed.ncbi.nlm.nih.gov/7444031/
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Comparative calibration is the broad statistical methodology used to assess the calibration of a set of p instruments, each designed to measure the same characteristic, on a common group of individuals. Different from the usual calibration problem, the true underlying quantity measured is unobservable. Many authors have shown that this problem, in general, does not have a unique solution. Most commonly used assumptions to obtain a unique solution are (i) one instrument is the gold standard (that is, unbiased) and (ii) the measurement errors of the p instruments are independent. Such constraints, however, may not be valid for many clinical applications, for example, the universal standardization project for dual X-ray absorptiometry (DXA) scanners. In this paper, we propose a new approach to resolve the comparative calibration problem when a gold standard is unavailable. Instead of the usual assumptions, we use external information in addition to data from the p instruments, to solve the problem. We address statistical estimation, hypothesis testing and missing data problems. We apply the new method specifically to the universal standardization project data where a group of individuals have been measured for bone mineral density (BMD) by three DXA scanners. We compare the results of the new method to currently used methods and show that they have better statistical properties.
BACKGROUND: Small increases in bone mass are commonly seen with existing treatments for osteoporosis, which reduce bone remodelling and primarily prevent bone loss. Since these drugs reduce but do not eliminate risk of fractures, an anabolic agent that would increase bone mass and potentially cure the underlying skeletal problem is needed. METHODS: We did a 3-year randomised controlled trial to find out the effects of 1-34 human parathyroid hormone (hPTH [1-34], 400 U/25 micrograms daily subcutaneously) in postmenopausal women with osteoporosis taking hormone-replacement therapy (n = 17). The controls were women taking hormone-replacement therapy only (n = 17). The primary outcome was bone-mineral density of the lumbar vertebrae, with bone-mineral density at other sites and vertebral fractures as secondary endpoints. FINDINGS: Patients taking hormone-replacement therapy and PTH (1-34) had continuous increase in vertebral bone-mineral density during the 3 years, whereas there was no significant change in the control group. The total increase in vertebral bone-mineral density was 13.0% (p < 0.001); 2.7% at the hip (p = 0.05); and 8.0% in total-body bone mineral (p = 0.002). No loss of bone mass was found at any skeletal site. Increased bone mass was associated with a reduction in the rate of vertebral fractures, which was significant when fractures were taken as a 15% reduction in vertebral height (p = 0.04). During the first 6 months of treatment, serum osteocalcin concentration, which reflects bone formation, increased by more than 55%, whereas excretion of crosslinked n-telopeptide, which reflects bone resorption, increased by only 20%, which suggests some uncoupling of bone formation and resorption. By 6 months, there were similar increases in both markers, which gradually returned towards baseline as the study progressed. Vertebral bone-mineral density increased most during the first year of PTH treatment. INTERPRETATION: We found that PTH has a pronouned anabolic effect on the central skeleton in patients on hormone-replacement therapy. PTH also increases total-body bone mineral, with no detrimental effects at any skeletal site. The increased vertebral mass was associated with a reduced rate of vertebral fracture, despite increased bone turnover. Bone-mass changes may be consistent with a reduction in all osteoporotic fractures. If confirmed in larger studies, these data have important implications for the treatment of postmenopausal osteoporosis.
STUDY DESIGN: A cross-sectional study to assess the lumbar spinal and proximal femoral bone mineral density in girls aged 12, 13, or 14 years with adolescent idiopathic scoliosis and to compare them with bone mineral densities of an age-matched control group. OBJECTIVES: To determine whether there is an association of osteopenia with idiopathic scoliosis, to compare bone mineral density in patients with scoliosis in different age groups with healthy controls, and to correlate bone mineral density with scoliotic parameters, including the pattern and magnitude of the curve. SUMMARY OF BACKGROUND DATA: Routine radiographs allow very limited assessment of osteopenia. Therefore, only a few studies have compared osteopenia in patients with scoliosis with that in healthy individuals. New techniques allow a more reliable quantification of the bone mineral state in adolescent idiopathic scoliosis. Available series in the literature either had a small sample population with inadequate controls or examined a large age range. METHODS: Using a dual energy x-ray absorptiometer, bone mineral density was measured in the predominant trabecular bone area, i.e., the lumbar spine (L2-L4) and bilateral proximal femur, in 81 girls aged 12, 13, or 14 years old with idiopathic scoliosis of various degrees of severity. Results were compared with those of 220 age-matched healthy control girls. RESULTS: In all three age groups, scoliotic patients had significantly lower bone mineral density in all measured regions than that in the control individuals (student's t test). Sixty-eight percent of the scoliotic individuals had a significantly reduced bone mineral density. Differences in bone mineral density between bilateral hips (paired t test) were not statistically significant either in scoliotic patients or in healthy control individuals. No differences in body weight, body height, or menarche status were found between the scoliotic and control individuals. Correlation studies showed that, in scoliotic patients, the values of bone mineral density did not correlate with the curve degree or curve pattern. CONCLUSIONS: There is a persistently lower bone mineral density in patients between 12 years and 14 years of age with idiopathic scoliosis. The decreased bone mineral density occurred in patients with idiopathic scoliosis before the age of 12 years, with no further progression from the age 12 to age 14, and did not correlate with the scoliosis degree or pattern. These findings suggest that the osteopenia in idiopathic scoliosis may be related to the primary etiology of the disease rather than secondary to the asymmetrical mechanical forces associated with the back deformities.