1. The skeletal effects of simple bed rest and re-ambulation were studied in a consecutive series of 34 patients (aged 18-60 years) hospitalized with low backache due to protrusion of a lumbar intervertebral disc. The bone mineral content of the second, third and fourth lumbar vertebrae was determined by dual-photon (153Gd) absorptiometry immediately after admission to the hospital, at the end of the bed-rest period (mean 27 days, range 11-61 days) and approximately 15 weeks later (range 11-24 weeks). 2. During recumbency a mean decrease in lumbar spine bone mineral content of 0.9% per week was observed. 3. Re-ambulation resulted in bone mineral gain, and restoration of lumbar spine bone mineral content was nearly complete after 4 months. 4. The findings suggest that the simple therapeutic bed-rest regimen leads to excessive vertebral bone loss. Recurrent bed-rest periods may predispose to spinal osteoporosis.

1. The skeletal effects of physical training were studied in a controlled trial involving 31 healthy women (aged 50-73 years) with previous Colles' fracture of the forearm. The bone mineral content of the lumbar spine and both distal forearms was measured by dual-photon (153Gd) absorptiometry. 2. The participants were allocated to either a physical exercise group or a control group. The former group followed a standardized exercise programme, exercising for 1 h twice weekly during 8 months. 3. Twenty-seven women completed the study. Lumbar spine bone mineral content of the exercise group increased by 3.5%, whereas that of the control group decreased by 2.7%. The rate of bone loss in the control group equalled that of age-matched normal women. 4. The changes in forearm bone mineral content appeared to be independent of the exercise. The bone mineral content of the previously fractured forearm remained nearly unchanged. The bone mineral content of the uninjured forearm decreased on average by 3.5%. 5. The data suggest that physical exercise can inhibit or reverse the involutional bone loss from the lumbar vertebrae in normal women. Physical exercise may prevent spinal osteoporosis.

1. Bone mineral content of the second, third and fourth lumbar vertebrae was determined in normal women and women with clinical osteoporosis by using dual-photon (153Gd) absorption. 2. A cross-sectional study of 70 normal (aged 19-88 years) showed a bone loss of 44% from the age of around 34 years throughout life. 3. Longitudinal data from 59 normal women confirmed that the vertebral bone loss started before the menopause. An accelerated bone loss amounting to nearly 6% per year was seen immediately after the menopause. The bone loss of older women was slower. 4. Mean lumbar bone mineral content of 36 women (aged 48-93 years) with recent fractures of their femoral neck after minor trauma equalled that of aged-matched normal women. Lumbar bone mineral content of the women with intratrochanteric femoral neck fractures was lower than that of the women with medial femoral neck fractures. 5. Mean lumbar bone mineral content of 72 women (aged 58-59 years) with primary osteoporosis was 41% lower than that of normal premenopausal women and 18% lower than that of age-matched controls. A weak inverse relationship between lumbar bone mineral content and the number of compression fractures was found. A weak inverse relationship between lumbar bone mineral content and the number of compression fractures was found. 6. Women with lumbar bone mineral content values below the 95% confidence limits for normal premenopausal women are at risk of future vertebral compression fractures, the fracture risk being inversely related to lumbar bone mineral content.

The effects of thyroid hormones and antithyroid treatment upon lumbar spine bone mineral content (lumbar BMC) were studied in a consecutive series of patients with myxoedema and thyrotoxicosis, respectively. All patients were investigated in the untreated state and 3-monthly during appropriate treatment for 1 year by using dual-photon [153Gd] absorptiometry. Patients with myxoedema (n = 8) did not differ from normal individuals as regards initial lumbar BMC, but levothyroxine-treatment caused significant reduction in this variable. The median decrease in lumbar BMC after 1 year was 8.9% (95% confidence limits 1.5-15.4%, P less than 0.05). This loss of bone might be attributed to an inappropriate increase in bone turnover in the euthyroid state. It is as yet uncertain whether it predisposes to spinal osteopenia. Median lumbar BMC in patients with thyrotoxicosis (n = 25) was 12.6% (2.0-16.6%, P less than 0.05) lower than that of normal individuals before the beginning of treatment. Lumbar BMC increased during antithyroid therapy. The median gain in bone mineral after 1 year was 3.7% (1.6-9.6%, P less than 0.01). These findings suggest that excess of thyroid hormones leads to negative spinal bone mineral balance. The revealed bone loss was clinically insignificant, however, and it appeared to be at least partially reversible after antithyroid treatment.

A new scanning dual-photon attenuation method utilizing a 153Gadolinium point source has been evaluated. The method allows precise in vivo determination of the bone mineral content of the lumbar spine (lumbar BMC). Lumbar BMC is expressed as the sum of the scan integrals of the second, third, and fourth lumbar vertebrae. The influence of crush fractures and varying amounts of soft tissue and fat is negligible. The coefficient of variation of repeated measurements ranges from 1.4% in normal pre-menopausal women to 2.6% in post-menopausal women with clinical osteoporosis. The radiation dose is low. The method is suited for cross-sectional and longitudinal studies of patients with lumbar osteopenia.