Metabolism of 59Fe-Sorbitol Complex in Man
Authors: G. Wetherley-Mein, J. G. Buchanan, U. H. Glass, L. C. Pearce
Journal: BMJ (1962)

~~~~~~~~~~~~MEDICAL JOURNAL which in due course will enable us to define the distribution in statistical -terms.In the meantime an R.V.D. ratio of less than unity indicates a vertebral density less than our standard.We are not yet prepared to define the reduction in bone density which justifies the use of the term " osteoporosis," but consider it axiomatic that vertebral bodies which are no denser than their disks are severely porotic.On this basis the data confirm our previous suggestion (Barnett and Nordin, 1960, 1961) that our original scoring procedure tends to underdiagnose osteoporosis-that is, it produces false negatives but no false positives.It would in fact appear from Fig. 7 that vertebral biconcavity develops at that stage in osteoporosis when the vertebral bodies have about the same radiographic density as the disks.It may seerm surprising that the vertebral bodies can even become less dense than the disks, but we attribute this to the replacement of bony trabeculae by marrow fat.Our results appear to resolve the problem of the difference between spinal and peripheral osteoporosis.We had previously suggested (Nordin, 1961 ; Barnett and Nordin, 1961) that peripheral osteoporosis might be a late stage in a disease process initiated in trabecular bone, particularly that of the spine, and had pointed out that the occurrence of pure peripheral osteoporosis might be an artifact of our original technique in that it failed to detect early spinal osteoporosis.This now appears to be the case.Examination of Fig. 6 shows that all our cases of peripheral osteoporosis with one exception have low R.V.D. ratios, and we are therefore satisfied that although spinal (that is, trabecular) osteoporosis may occur without peripheral (that is, cortical) osteoporosis, the reverse does not occur.In generalized osteoporosis the first loss of bone is trabecular and only later does cortical loss occur.This accords.with the experimental evidence of the effect of negative calcium balance in animals (Nordin, 1960), and is therefore compatible with the concept that clinical osteoporosis could be due to prolonged negative calcium balance.Summary A method is described for assessing the density of the lumbar vertebrae by comparison with the intervertebral disks.This procedure is designed to eliminate the effect of soft-tissue variation.A lateral tomogram is obtained through the centre of the lumbar spine and of a dissected specimen of lumbar spine mounted in formol-saline and placed next to the subject.The film images of the spine and standard are fed through a Laurence-Locarte recording densitometer and the difference between the average density of the disks and the average density of the bodies is determined.This difference in the spine is divided by the same difference in the standard, and the ratio is called the relative vertebral density.The results obtained are compared with the x-ray scores of Barnett and Nordin.This comparison suggests that vertebral biconcavity develops at the stage when the vertebral body is of about the same density as the intervertebral disk.In severe osteoporosis the vertebral bodies are less dense than the intervertebral disks.