Intra-rater reliability of B-mode ultrasound in the measurement of soft tissue thickness and composition over the lateral proximal femur

Objectives Comprehensive characterization of soft tissue composition and distribution over the lateral proximal femur is necessary to improve our understanding of fall-related hip fractures; however, a protocol that produces reliable data is needed. Accordingly, the aim of this study was to assess the intra-rater reliability of B-mode ultrasound measured muscle, adipose, and total soft tissue thicknesses over the lateral proximal femur in a simulated sideways fall configuration. Methods Twenty-five young adults (12 males, 13 females, age (SD) = 20.8 (1.9) years) underwent B-mode ultrasound imaging of 12 locations over their lateral proximal femur while in a side-lying position. Side-lying was chosen to allow imaging of the tissues impacted during a lateral fall event. Muscle, adipose, and total soft tissue thicknesses were measured at each location (further grouped into posterolateral, lateral, and anterolateral locations for statistical analysis) and two-way mixed model absolute agreement intraclass correlation coefficients (ICCs) and standard error of measurement were used to assess reliability of tissue type, location, and sex. Results ICCs were excellent (ICC >0.9) for each tissue type, measurement location, and sex. There were interactions between tissue type, measurement location, and sex on reliability. While measures of adipose thickness were excellent across all conditions, reliability of muscle and total soft tissue thickness measurements were dependent on measurement location and sex. Conclusions This ultrasound imaging protocol demonstrated good-to-excellent reliability of soft tissue-specific thickness measurements over the lateral proximal femur. This protocol has implications for subject-specific hip fracture risk screening tools and biomechanical models of impact dynamics that incorporate biofidelic soft tissue morphology.