Quantitative bone mineral assessment at the forearm: a review

Bone mineral density and geometric properties of the human forearm can be measured to determine the amount of bone or bone loss at the scanning site and to predict the risk of forearm fractures. These forearm measurements are also used to estimate bone mass at remote anatomical locations and thereby estimate the risk for spine, hip and other fractures. The peripheral location of the human forearm, with its relatively small amount of surrounding soft tissue, improves the accuracy and the precision of bone mass measurement and has made this site an early choice for the assessment of a subject's bone mineral status. Furthermore, the anatomy of the human radius enables the examination of both cortical and cancellous bone. This review describes the procedures for non-invasive bone assessment at peripheral sites including some of the more recently developed systems dedicated to assessment of the distal radius. The accuracy, precision and normative values they provide are presented. Responses to different forms of therapies as well as the ability to discriminate or predict osteoporotic fractures are also assessed. Low radiation dose, comfortable and fast handling, moderate cost, and a strong association with the risk of non-spine fractures, promote the use of forearm scanning as a widely applied screening procedure for the detection of generalised osteoporotic bone loss. However, a higher accuracy of fracture risk prediction at the spine or at the hip can be achieved by a direct bone density measurement at these sites. The monitoring of treatment at the distal forearm appears to require a longer follow-up time due to its decreased responsiveness compared with such highly trabecular load-bearing sites as the spine and the proximal femur.