Measuring tibial cortical bone status by ultrasonic velocity

Post-menopausal osteoporosis has become a serious public health problem with the increase of the geriatric population. Dual energy x-ray absorptiometry (DEXA) is the most common method for diagnosis of osteoporosis by quantitative change of bone, but recently there is increasing interest in measuring both qualitative and quantitative changes of bone by ultrasound. This study measured ultrasound velocity of anterior tibial cortex to evaluate the feasibility of detecting cortical bone status by speed of sound (SOS).

SOS in anterior tibial cortex was measured on 205 females referred from clinicians for routine bone mineral density (BMD) measurement. These females were divided into 2 groups. Group 1 consisted of 170 females aged from 30 to 75 years (mean: 55.2 +/- 9.3 years), who never received estrogen therapy. Group 2 consisted of 35 females in the post-menopausal status aged ranged from 45 to 69 years (mean: 51.5 +/- 3.5 years), who had received estrogen gel or oral estrogen tablet (0.625 mg/day) replacement therapy for prevention of postmenopausal osteoporosis for a period of 6 to 68 months (mean: 25.3 +/- 2.3 months). For precision test, 3 volunteers whose SOS was measured by 2 different operators were also enrolled in our study. BMD by DEXA of L-spine and/or hip was also performed on the same day of SOS examination. We analyzed the precision of this new method, calculated mean value of SOS to see if there was any difference with respect to pre- at, and post-menopausal status between estrogen users and nonusers by SOS, and tried to find the relationship of SOS with body habitus and BMD.

Mean value of SOS of group 1 females was 3852 +/- 150.3 m/s, with peak value in the fourth decade. There were inverse correlation of SOS with age (r = -0.36, p < 0.0005) and the period after menopause (r = -0.32, p < 0.0005). The decreasing rate of SOS per decade from 31 to 50 years of age was 1.7%, while that of 51 to 70 years was 4.3% in group 1 females. With regard to menopausal status, there was significant difference of SOS between pre- and post-menopausal females (p = 0.01, ANOVA test), between at and post-menopausal females (p = 0.02). Significant difference (p < 0.05, ANOVA test) between group 2 estrogen users and group 1 postmenopausal nonusers was also noted. There was no evidence of correlation of body weight or height with SOS. Both inter- and intra-operator precision of SOS was under or equal to 0.32%. Moderately correlation between SOS and BMD was noted.

Our study demonstrated good precision in SOS measurement of tibial cortical status. It was inversely correlated with age and post-menopausal period; it also significantly discriminated estrogen users from nonusers, and pre-, at from post-menopausal subgroups. However, for further evaluation of the relationship between SOS and the most severe complication of osteoporosis, i.e. osteoporotic fracture, population-based long-term followup is still required.