Assessment of bone mineral. Part 2.

A number of different techniques are available to study bone mineral. Those based on radiographs are helpful as an initial approach to the symptomatic patient with advanced disease, but they do not have the sensitivity to detect early bone loss, to assist in the estimation of fracture risk, or to monitor effects of treatment in controlled drug studies. A radiograph of the spine and hip, however, should be the first step before other tests are ordered. Photon absorptiometry methods or CT-based tests are currently most attractive as second-line approaches. Of these, photon absorptiometry is more widely tested clinically and allows studies of predominantly cortical or trabecular bone sites and total skeletal calcium. Although all of this cannot be done reliably with one instrument under routine laboratory conditions at present, it may well become possible in the near future. Of the CT-based procedures, the forearm scanner is very attractive because of its high precision and accuracy and the fact that it allows measurement of trabecular bone only. The technique is restricted to the forearm and may not be versatile enough for modern clinical requirements. A similar comment may be applicable to neutron-activation techniques of the hand, forearm, or spine. Low-level counting and the handling of neutron sources are not widely known techniques in many laboratories, and this will restrict their use in clinical practice. At this time there is no optimal technique available for mass screening for early osteoporosis. Dual-photon absorptiometry of the spine has been in use in our institution as the method of choice in selected patients for early detection of osteoporosis. However, for screening purposes the radius is still a very attractive bone to measure. At the currently used measuring sites, however, it does not have the sensitivity required to indicate spinal bone loss. Perhaps measurements closer to the distal end, where the trabecular-to-cortical bone ratios approach that in the spine, could be more sensitive. The difficulty of relocating the arm for photon absorptiometry can perhaps be solved for photon absorptiometry, or may be resolved by CT of the forearm. Correlation of the extreme distal radius with the spine is necessary to answer this question.