ASSESSING BONE QUANTITY BY PQCT

We have tested the ability of the XCT960A to detect bone loss in OVX-r ats, as well as bone gain in the proximal tibial metaphysis of healthy rats treated with hPTH(1-34). The results demonstrated that high prec ision can be achieved, with CV's for most measurement parameters in th e range of 1.6 to 5.9% being obtained in vivo with repositioning of an imals. Significant changes in bone parameters in the tibia were observ ed already at 2 weeks following OVX or PTH-therapy, while whole bone m ass measured in the tibia by DEXA ex vivo did not change significantly for up to 24 weeks. For the proximal rat tibia a location 5mm distal to the knee joint was identified as an optimal site. At this location, cortices are fairly parallel thus reducing the partial volume effect, the area is relatively rich in cancellous bone increasing the magnitu de of bone gain or loss, and the site (2mm below the growth plate) is relevant for comparisons with histomorphometric measurements. The resu lts demonstrate that pQCT can be adapted for use in small animals such as rats, and that it is a sensitive, reproducible, non-invasive metho d available to monitor changes in bone mass, bone density, and geometr ic properties. Future studies should help to establish whether the mom ent of inertia, moment of resistance and the newly added bone strength index provided by the machine are predictive in any way for bone stre ngth as obtained from biomechanical testing procedures. Peripheral QCT in small animals is an important addition for drug evaluation because it is more sensitive than DEXA and allows for shorter duration of exp eriments. This non-invasive method can reliably measure changes in can cellous and cortical bone mass over time following ovariectomy or admi nistration of the bone anabolic hormone hPTH(1-34). pQCT should be vie wed as a complimentary technique to static and dynamic histomorphometr y, which does not replace either of these methods. Its value in the fi eld of basic research should be evaluated.