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SUMMARY The rate of spinal trabecular bone loss during one year was measured in 54 patients with inflammatory bowel disease. The mean change in spinal bone mineral content was -5 1 mg/ml K2HPO4, representing 3% of the initial bone mineral content. The rate of bone loss showed a significant negative correlation with body mass index (r=-0.276, p<005) but no other significant correlations were found with other clinical or biochemical indices, including the total amount of prednisolone taken during the course of the study. Eleven patients had bone loss greater than 15 mg/ mVyear; these included four non-steroid treated patients, two of whom had disease confined to the large bowel. The results indicate rapid rates of bone loss in some patients with inflammatory bowel disease over the course of one year. Although steroid therapy and malnutrition are likely to be contributory factors in some patients, other, as yet unidentified, risk factors also operate. The rapid bone loss observed in some patients emphasises the need for effective prophylactic regimes.Osteoporosis has been reported in association with intestinal disease'`and we have recently shown an increased prevalence of spinal osteoporosis in a large unselected group of patients with inflammatory bowel disease, using quantitative computed tomography.5 In some patients, particularly young women with amenorrhoea and high dose steroid therapy, severe clinical manifestations of osteoporosis were seen with bone pain, spinal deformity and height loss resulting from vertebral crush fractures.

A relationship has been derived between the in vivo concentration of calcium hydroxyapatite and the in vitro concentration of K2HPO4 solution in a single-energy quantitative computed tomography (QCT) bone-mineral determination. Under certain simplifying assumptions this relationship is linear. The gradient term has been calculated as a function of scanner effective energy using the measured variation of solvent water density with K2HPO4 concentration; it ranges from 1.17 at 60 keV to 1.21 at 80 keV. The intercept term has been calculated as a function of effective energy, patient age and trabecular bone volume (TBV) by modelling the constituents of whole trabecular bone and using published normal composition data. It varies from about 15 to 25 mg cm-3 at an effective energy of 70 keV and within a TBV range of 5 to 20%. This intercept term may be used as an additive correction which improves the accuracy of single-energy QCT results without significant loss of precision. However, the method is limited by the uncertainties of tissue composition in an individual patient.

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