Ultrasound velocity and dual-energy X-ray absorptiometry in normal and pagetic bone.

Bone affected by Paget's disease is known to be dense but more prone to fractures. It is proposed that dual-energy X-ray absorptiometry (DXA) and quantitative ultrasound (QUS) assess different aspects of the skeletal status. In this study, we used Paget's disease of the tibia as a model to explore this. Ten patients with Paget's disease affecting a single tibia were investigated with the normal side acting as the control within each individual. Tibial speed of sound (SOS) was measured at the midpoint of the affected and control tibiae using a Soundscan 2000 (Myriad Ultrasound System, Rehovot, Israel) device. Bone mineral density (BMD) of the tibia was measured at a level corresponding to the site of the tibial ultrasound using a QDR-2000+ (Hologic, Inc., Waltham, MA). The mean bone area and estimated volume in the pagetic tibia was greater than that in the normal tibia (bone area: 25.10 +/- 8.00 vs. 20.23 +/- 5.43 cm(2), p = 0.017; estimated bone volume: 68.79 +/- 41.99 vs. 43.62 +/- 22.56 cm(3), p = 0.02), reflecting the bone expansion characteristic of Paget's disease. The bone mineral content (BMC) was more markedly increased in the pagetic tibia (27.38 +/- 12.98 vs. 14.39 +/- 6.14 g, p = 0.003) and, consequently, areal bone mineral density (BMD) was also markedly increased in the pagetic bone (1.09 +/- 0.38 vs. 0.77 +/- 0.44 g/cm(2), p = 0.018). There was no significant difference in the estimated volumetric BMD between the pagetic and the normal tibia (0.48 +/- 0.24 vs. 0.47 +/- 0.51 g/cm(3), p = 0.96). In contrast, the mean tibial SOS in the leg affected by Paget's disease was significantly lower than in the unaffected leg (3228 +/- 234 vs. 3840 +/- 164 m/sec, p < 0.001). When expressed as a z score using the normal limb as reference, areal BMD was 0.72 SD higher in the affected limb, whereas tibial SOS was 3.72 SD lower. We conclude that tibial SOS detects important changes in bone quality in Paget's disease of bone, which are unrelated to calcium content.