Reproducibility of phalanx osteosonography and relation with forearm peripheral quantitative computed tomography: single finger versus average measurement on the last four fingers.

The aim of this study was to evaluate the in vivo short-term reproducibility of amplitude-dependent speed of sound (AD-SOS) measured at the proximal phalanx, using an Igea DBM Sonic 1200 device, as well as its relationship with bone mineral density of the ultradistal radius, assessed using peripheral quantitative computed tomography (pQCT). In particular, the authors wished to evaluate whether average measurements on the last four fingers, as recommended by the manufacturer, yielded or not more information than measurements on one single finger. For the precision study, the authors carried out phalanx osteosonography ten times once every other day in ten healthy young women. To compare with pQCT of the radius, 37 women referred for screening of osteoporosis (mean age 60 years) were studied. AD-SOS was reported for each finger separately, as well as an average; pQCT (XCT 960 Stratec) yielded trabecular (BMDt); cortical (BMDc); and total (BMDtot) bone mineral densities, as well as the cortical area (Ac). The reproducibility of AD-SOS was significantly higher for the middle finger (mean coefficient of variation (CV) 1.1%) and the index than for the ring and small (mean CV 2.7%) finger. The middle finger consistently showed the best correlations with pQCT variables; the relationships involving BMDc (r = 0.54), BMDtot (r = 0.62) and Ac (r = 0.61) were stronger than that with BMDt (r = 0.34). The authors conclude that phalanx AD-SOS is moderately correlated with BMD of the ultradistal radius--at least when it includes the cortical component--and that reporting AD-SOS for the middle finger--instead of an average value--improves the reproducibility and possibly the relevance of phalanx osteosonography.