1990, The British Journal of Radiology, 63, 370-372

Proceedings of The British Institute of Radiology What shall we do about osteoporosis? Abstracts of papers presented at a joint all-day meeting organized by the BIR and the National Osteoporosis Society held at the Windeyer Building, Middlesex Hospital, Cleveland Street, London W1 on Wednesday, 22 November 1989 Chairman: Professor P. J. Ell What is osteoporosis and why is it a major disease? by I. Fogelman The physics of bone density measurement, by I. Cullum. Abstract not received Single and dual y photon absorptiometry: relative merits, by R. Valkema The role of quantitative computed X-ray tomography, by J. Adams A comparison of dual energy absorptiometry, by M. Fischer and B. Kempers First data on a UK normal range for dual energy X-ray absorptiometry, by M. L. Hall, J. Heavens, I. D. Cullum and P. J. Ell Hormone treatment—efficacy and safety, by H. Jacobs. Abstract not received Fracture prediction in osteoporosis, by A. Horsman Role of DEXA in non-osteoporotic bone disease, by L. Rosenthall Advances in the investigation and treatment of established osteoporosis, by P. Meunier. Abstract not received What is osteoporosis and why is it a major disease? I. Fogelman Department of Radiology, Guy's Hospital, London Osteoporosis is a disease in which there is too little bone and individuals are at increased risk of fracture, often without significant trauma. The clinically most relevant fractures are those of the forearm, spine and hip. Fracture of the hip has received the most attention as, in addition to the high morbidity, the need for hospital admission and escalating financial costs, there is significant mortality of around 20% as a result of related complications. However, fracture of the spine should not be forgotten, as this tends to affect a relatively younger group of women who may have to look forward to many years of chronic discomfort and increasing deformity. It is of concern that the incidence of osteoporotic fracture has been found to be increasing in some countries, e.g. Scandanavia and the United Kingdom. The cause for this is not apparent. Nevertheless while individuals are living longer it would appear that there is a deterioration in skeletal quality from one generation to the next. Hospital costs are rising, individuals are living longer and the incidence of osteoporosis appears to be on the increase. The problems relating to osteoporosis can no longer be ignored and if positive steps are not taken to tackle them then, leaving aside the issues of morbidity and mortality, thefinancialimplications are frightening. In the United States it has been suggested that the cost of hip fractures may eventually bankrupt the health services!

Single and dual y photon absorptiometry: relative merits R. Valkema Department of Diagnostic Radiology, Division of Nuclear Medicine, University Hospital, Leiden, The Netherlands Single photon absorptiometry (SPA) and dual photon absorptiometry (DPA) have gained widespread acceptance as noninvasive techniques to measure bone mineral content (BMC). Since reduced bone mass is one of the most important risk factors for fractures, DPA and SPA are used to select patients who need preventive measures or therapy, as well as to monitor the effects of the installed therapy. With SPA, only measurements at the appendicular skeleton are feasible. Although there is a significant correlation between BMC at the forearm and

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the spine or hips, this correlation is not close enough to predict axial BMC from appendicular measurements. Furthermore, changes in BMC at the midradius seem to correlate not at all with changes in BMC at the lumbar spine. With DPA the axial BMC can be measured, in particular at the vertebral column and hips, which are the most important sites for osteoporotic fractures. The reported precision and accuracy of DPA are approximately 1-3% under optimal conditions, but in everyday clinical practice errors twice as large are likely. The accuracy and precision errors of DPA will be worse in patients with low bone mass, scoliosis, osteophytes, aortic calcifications and/or inhomogeneous distribution of paravertebral fat. Another major cause of error is the relatively low yield of photons emitted from the 153-Gd source. As a result, the spatial resolution of DPA is less than optimal with difficulties in selection of the region of interest. The changes in bone mineral mass range from less than 1% to approximately 3% per year in most cases and therefore, the precision of DPA is insufficient for reliable follow-up of individual patients. The recently introduced technique of dual energy X-ray absorptiometry (DEXA) is based on the same principles as DPA, but instead of a radioactive source it uses an X-ray tube. Its precision is better than the precision of DPA, so DEXA may fulfil the promise that DPA has made.

The role of quantitative computed tomography J. E. Adams Department of Diagnostic Radiology, University of Manchester, UK Quantitative computed tomography (QCT) is now established as an important non-invasive technique of bone mass measurement. It is applied principally to the spine, but measurements have also been made in peripheral sites. Single sections are performed through the middle of vertebrae generally T,2 to L3, using a low dose technique (80 kV, 70 mA, 2s). This results in a radiation dose of 1.75-2.0 mGy for each examination (1/5 of the dose of a lateral lumbar radiograph). To correct for scanner instability or beam hardening, scanning is performed with a bone equivalent calibration phantom to convert attenuation value for the region of interest (ROI) into mineral equivalents (mg/ml). Original phantoms contained K2HPO4 solutions, but The British Journal of Radiology, May 1990

Proceedings of the British Institute of Radiology because these showed some change with time, solid hydroxyapatite phantoms are now being developed. For any measurement technique to be clinically useful, high precision is a prerequisite. Careful attention to scanning details and patient positioning is essential. Automation of scan plane and ROI selection results in a precision of 1-2% for spinal QCT. Measurements from different scanners may not be identical and in longitudinal studies it is imperative that the calibration phantom is not changed. Marrow fat will cause some underestimation of mineral content of trabecular bone. Accuracy can be improved by using dual energy QCT, but with reduction in precision, increase in radiation dose and considerable technical effort. Monochromatic isotope CT scanners have been developed for peripheral skeletal sites (radius, tibia). In common with other non-invasive techniques (SPA, DPA, DPX) QCT can measure integral (cortical and trabecular) bone. However, QCT is unique in allowing separate estimations of trabecular and cortical bone. Since trabecular bone is some eight fold more active metabolically than cortical bone, QCT is the most sensitive method for monitoring changes in trabecular bone in response to treatment and serially in patients with metabolic bone disease. It can detect age-related changes in bone mass in the normal population, and the accelerated loss which occurs at the menopause. Fractures are likely with QCT values below 110 mg/ml and inevitable below 60 mg/ml ("fracture threshold"). Although, as with other techniques, in older populations there is an overlap of QCT values in osteoporotics and normal subjects of the same age.

Inter-unit variation of bone densitometry systems M. Fischer and B. Kempers Institute of Nuclear Medicine, Staedtische Kliniken, Kassel, FRG The different bone mineral content (BMC) of European and American population has been discussed recently. The aim of this study was to compare the intra- and inter-unit variation of bone densitometers (BD) of different companies using an animal spine as a phantom and to build a phantom for cross calibration. Six vertebras of a pig were encapsulated in 16 cm of soft-tissue-equivalent material. Three vertebras of this phantom were measured with BDs using either radionuclide sources (n = 6) or X-ray tubes (n = 3). In each series the phantom was measured several times. To exclude the inaccuracy of BDs caused by varied soft-tissue compositions, the BMC of the phantom was measured with different overlying tissue (water and/or fat). Whereas the inter-unit variation was as much as 20%, the intra-unit variations were less than 1% in all systems but two, in which a coefficient of variation of 5% was observed. These two BDs were more than 5 years old. Overlying the phantom with water (4 and 8 cm) and/or fat (3.5 and 7 cm), different results were observed. Some BDs showed variations of basal values of about 8-10%, others were not influenced. During a long-term measurement of the phantom with two BDs, the coefficient of variation was less than 2%. The inter-unit variation of bone densitometry systems may be a result of various calibrations, whereas the under- or overestimation of BMC, depending on different overlying soft tissue, may be caused by different software algorithms. Because of these differences, a comparison of BMC values measured by different BDs is problematic. We therefore built a phantom with cylindric bodies with different hydroxyapatite content for cross calibration of BDs. By using such phantoms, a standardization of BDs should be possible.

Vol. 63, No. 749

First data on a UK normal range for dual energy X-ray absorptiometry M. L. Hall, J. Heavens, I. D. Cullum and P. J. Ell The Institute of Nuclear Medicine, University College and Middlesex School of Medicine, Mortimer Street, London WIN 8AA Dual energy X-ray absorptiometry (DEXA) is a new technique for the measurement of bone mineral density. The results given are in g/cm2 and have a different value from previous dual energy methods. The normal range of bone density for US subjects is supplied with the machine (Hologic 1000); however, it has been shown that the results vary between populations. It is for these reasons that we studied the range of bone density in 207 British women from the ages of 4 to 70. Strict inclusion and exclusion criteria were applied and the resulting mean and standard deviations compared with the US data. The UK results are shown below (Table 1). From our cross sectional data there is no obvious peak in bone density, longitudinal studies will be needed to confirm the timing of any peak bone mass. Bone density values decreased after the menopause and the mean result was significantly different from any premenopausal age group. Comparison with the US range is adequate but a specific UK range from more subjects is preferable. Table I. The range of bone density: UK results Age

Mean bone mineral density (g/cm2)

Standard deviation

20-29 30-39 40-49 50-59 60-69

1.053 1.058 1.063 0.923 0.821

0.085 0.098 0.134 0.128 0.121

Fracture prediction in osteoporosis A. Horsman MRC Bone Mineralisation Group, The General Infirmary at Leeds, Great George Street, Leeds LSI SEX By means of a stochastic model that simulated falls and bone loss from the proximal femur in an ageing cohort, it was shown that in women, up to the age of about 70, the risk of fracture of the hip following a fall increases exponentially with decreasing bone mineral density (BMD) in the femoral neck. To account for the continuing increase in the age-specific incidence of hip fracture in higher age groups, it was necessary to include in the model an age-related risk multiplier that was independent of BMD and rose rapidly over the age of 70. The proportion of all hip fractures occurring in an ageing female cohort was estimated in relation to individual membership of groups classified by BMD at maturity and/or rate of decrease of BMD in middle age. The model predicted that about 60% of all fractures occur in those 25% of women who at maturity have the lowest values of BMD. Estimates of lifetime risk of hip fracture based on an individual's measured value of BMD at any age (A) and life expectancy (L) were also calculated. For any particular values of A and L, the lifetime risk was shown to rise rapidly as BMD decreases. Such risks could be modified by long-term therapy which affected the course of age-related bone loss and/or the way in which the risk of falls increased with age in the individual. The likely reduction in fracture incidence resulting from large-scale prophylaxis was evaluated taking into account its possible effects on bone loss and falls.

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Proceedings of the British Institute of Radiology

Role of DEXA in non-osteoporotic bone disease L. Rosenthall The Montreal General Hospital, McGill University, Montreal, Canada A review was undertaken of all patients seen at the Metabolic Bone Unit during the last year. An analysis of the nonosteoporotic metabolic bone disorders yielded the following results. Renal dialysis: 48 patients on dialysis for a mean (sd) of 6.5 (5.2) years had a mean (sd) age-matched spinal BMD of 101 (17)%, but 8/48(17%) patients had BMDs exceeding 2 standard deviations, which is a significant occurrence of sclerosis. The mean (sd) BMD of the hips in 16 patients was 99.3 (20.8)%, but 4/16 (25%) patients had BMDs in excess of 2 standard deviations. Anorexia nervosa: the mean (sd) agematched spinal BMD of 16 women (mean age 32 years) was 78.9 (11.4)%, which is more than 2 standard deviations below normal. Hypogonadism: 15 male patients of mean (sd) age

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38(13) years registered a mean (sd) spinal BMD of 72.2 (14.4)%, more than 2 standard deviations below normal. Similarly, hypogonadism in 10 female patients with a mean (sd) age of 27 (6) years had a mean (sd) spinal BMD of 78.6 (14.4)%: significantly low. X-linked hypophosphatemia (hyperphosphaturia): there were 14 patients in this catagory and all had been treated for many years with vitamin D and phosphates. The mean (sd) spinal BMD was 131(31)%, 3 standard deviations above normal. This intense sclerosis was not always reflected in the hip BMDs in the few determinations that were done. Idiopathic juvenile osteoporosis: four female patients, aged from 10 to 14 years, had a mean spinal BMD of 65% of that predicted for their age and weight. Osteogenesis imperfecta: five patients, one male and four female, aged from 10 to 15 years, yielded a mean spinal BMD of 67% of that expected for their age and weight.

The British Journal of Radiology, May 1990

What shall we do about osteoporosis? The British Institute of Radiology. London, 22 November 1989. Abstracts.

1990, The British Journal of Radiology, 63, 370-372 Proceedings of The British Institute of Radiology What shall we do about osteoporosis? Abstracts...
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