RESUMO
We assessed a method for the measurement of ultrasound velocity in cortical bone of the human tibia using a probe designed to minimize the effects of surrounding soft tissues. Of four different measurement values, the maximum velocity (average of the five highest readings) gave the lowest errors of reproducibility in relation to the population variance (standardized coefficient of variation = 1.8%). The maximum velocity varied according to the tibial site measured and for practical reasons the mid-tibial site was chosen for further study. The short-term intra- and inter-observer reproducibilities (coefficients of variation) were 0.35% (n = 22) and 0.50% (n = 27) respectively. Long-term reproducibility over 4 months in 31 subjects was 0.68%. There was no significant difference in maximum ultrasound velocity between the dominant and nondominant tibia in 78 women (3764 +/- 209 vs 3763 +/- 199 m/s). Tibial ultrasound velocity was significantly higher in 73 premenopausal women (3999 +/- 102 m/s) than in 129 women referred for assessment of postmenopausal osteoporosis (3780 +/- 168 m/s), 26 women with steroid-induced osteoporosis (3790 +/- 188 m/s) and 4 women with hyperparathyroidism (3575 +/- 261 m/s). In premenopausal women, ultrasound velocity did not correlate significantly with age, height, weight or body mass index. In women with postmenopausal osteoporosis, ultrasound velocity decreased with age after the menopause (r = -0.47, p < 0.0001) and body weight exerted a weaker protective effect. The apparent annual decrease in velocity with age in postmenopausal osteoporosis (8.5 m/s) was comparable to the error of reproducibility. We conclude that the technique for measuring tibial ultrasound velocity is highly reproducible in relation to the distribution of values in the population and is sensitive to age- and osteoporosis-induced changes in bone. Further studies are required to examine its relationship to other indices of skeletal status to determine the biological and clinical relevance of the technique.
