The Use of Peripheral QCT in the Evaluation of Bone Remodelling

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Abstract
Procedures to evaluate the bone status in a noninvasive way comprise absorptiometric methods such as single photon absorptiometry (SPA) or dual x-ray absorptiometry (DXA), and computer tomographic methods of the axial skeleton (axial QCT) and the peripheral skeleton (pQCT). This report focuses on the metfiodology and the application of peripheral quantitative computed tomography. pQCT is a low risk procedure with the potential to perform precise bone density determinations separately for trabecular bone and compact bone. Long-term reproducibility of 0.3% in patient examinations is achievable with a special multislice technique. Due to its low dose and its high precision, pQCT is particularly suitable for serial examinations. It is most useful in detecting "high risk" patients in the early postmenopause and for optimizing treatment procedures. In the early postmenopause, approximately one-third of otherwise healthy women suffer from an excessive bone loss that can be prevented by estrogen substitution; we give the example of a controlled, randomized study with transdermally applied estradiol. The concept of "fast bone losers" and "slow bone losers" appears to be generally applicable and may be the basis of a tailored treatment scheme. Bisphosphonates, calcitonin, and estrogens are substances able to stop a high bone loss. Fluorides, having the potential to increase bone mass, should be used only in slow bone losers to avoid treatment induced fractures. While trabecular bone and cortical bone are affected in synchrony in the early postmenopause, differential effects on trabecular and cortical bone can be observed in hyperparadiy-roidism, corticosteroid or fluoride treatment. The high spatial resolution provided by pQCT permits a "compartmental" analysis of bone structure. Research under way should allow a quantitative evaluation of the three-dimensional bone architecture at the same sites where the bone density is measured. The combination of bone density and structural analysis provides an improved fracture risk prediction and a refined understanding of the bone remodelling processes during disease and therapy (C) Lippincott-Raven Publishers.

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