Calcaneal ultrasound attenuation as a predictor of bone density: Does the region of interest or loading influence the repeatability of measurement?

Abstract

Introduction: It is well documented that sporting activities are important to increase bone mass. Depending on the quality and type of sport the amount of bone increment will vary. The attenuation of ultrasound as it passes through the calcaneal bone provides quantitative information about the density and structural properties of bone and is a clinically useful predictor of osteoporotic fracture risk in adults. Current ultrasound systems, however, assess different regions of interest (ROI) of the calcaneus, yield different attenuation values, involve different levels of lower limb loading and are likely prone to different levels of error. This study evaluated the repeatability of measures of ultrasound attenuation at three calcaneal ROI under varying levels of load. Methods: A custom-built transmission-mode ultrasound system was used to measure ultrasound attenuation in the calcaneus of 20 healthy participants (mean (±SD) age, 41.8 ± 19.6 years; height, 1.70 ± 0.17 m; and weight, 71.3 ± 23.3 kg). Repeated measurements were performed at three ROI (BW, JA, FG) and under four loading conditions (non-weightbearing, semi-weightbearing, bipedal stance, unipedal stance). Agreement between measures was evaluated using the Standard Error of Measurement (SEM) and limits of agreement (LA). Potential differences in attenuation between ROI, loading and measurement occasions were assessed using repeated measure analysis of variance ( 0.05). Results: Ultrasound attenuation ranged from 58.0±32.0 to 77.2 ± 27.6 dB/MHz across all conditions. There was a statistically significant difference between all ROI (F = 11.7, P = <0.001), which was moderated by loading (F = 2.4, P = 0.03).The narrowest LA for repeated measures of attenuation ranged between 25.7 dB/MHz and 11.6 dB/MHz across all sites. The SEM for attenuation was approximately 10 dB/MHz for both the FG and JA ROI during non-weightbearing and tended to reduce to approximately 5 dB/MHz with full weightbearing. Discussion: ROI and calcaneal loading are important considerations for measures of ultrasound attenuation at the calcaneus. Although measures of ultrasound attenuation are dependent on the ROI, lower limb loading tended to lower attenuation and improve the repeatability of measurements across sites. Given that the LA were 1.7 times smaller during unipedal stance than in non-weightbearing, calcaneal loading may be a useful method to improve the minimal detectable difference of the measurement. Conflict of interest statement: The authors declare no conflicts of interest.