Intrarater and Interrater Reliability of Quantitative Ultrasound Speed of Sound by Trained Raters at the Distal Radius in Postmenopausal Women.

Background and purpose: Quantitative ultrasound (QUS) performed at the distal radius shows potential as an effective tool for evaluating fracture risk, especially in postmenopausal women, but the reliability of this tool has not been reported in this patient population. This study investigated the within-day intrarater and interrater reliability of trained raters performing QUS measures at the distal radius of postmenopausal community-dwelling women.

Methods: Eighteen women between the ages of 56 and 87 years were recruited from senior centers in the Greenville area of South Carolina and consented to participate. A QUS bone sonometer was used in this study; the trained raters performed 3 repeated speed of sound (SOS) measures at the nondominant radius of each participant on the same day. Intraclass correlation coefficients (ICCs) were calculated (model 3,1 for intrarater and 2,3 for interrater reliability) to determine the reliability within and between raters. In addition, we calculated the standard error of measurement (SEM) and the minimal detectable change at 95% confidence interval (MDC 95 ).

Results: The within-day intrarater reliability was excellent for both physical therapist raters (ICC (3,1) ranging from 0.93 to 0.91). The SEM and MDC for the within-day intrarater reliability measures were small for both raters (SEM = 36.79-38.75 or 0.92%-0.97% of the pooled mean; MDC 95  = 101.99-107.40). The interrater reliability for SOS measurements using radial QUS was good with an ICC (2,3) of 0.77 (95% CI, 0.36-0.92) for 3 averaged measures. The SEM and MDC were larger for the interrater reliability measures (SEM = 62.79 or 1.57% of the pooled mean; MDC 95  = 174.05).

Conclusions: Quantitative ultrasound SOS measurement at the distal radius showed excellent within-day intrarater and good interrater (when 3 measures were averaged) reliability in community-dwelling postmenopausal women. The SEM and MDC 95 were also low for interrater reliability when a mean of 3 trials was used. This study is the first to demonstrate that this particular QUS device at the radius may be a reliable fracture risk screening tool for postmenopausal women.