Bridging Muscle and Bone Health: Rectus Femoris Ultrasound Parameters Predict Osteoporosis and Identify Low Muscle...

Background/Objectives: Sarcopenia is characterized by a decline in muscle mass and function. Its association with osteoporosis-referred to as osteosarcopenia-is linked to increased risks of falls, fractures, frailty, and mortality. Therefore, there is a growing need for accurate and accessible tools to assess muscle mass. Ultrasonography has emerged as a promising modality in recent years. The aim of our study was to compare rectus femoris ultrasound parameters in postmenopausal women with osteoporosis to healthy controls and to evaluate its diagnostic performance against a reference method. Materials and Methods: A cross-sectional prospective study was conducted including 88 postmenopausal women with a mean age of 65.7 ± 7.5 years. Functional status was evaluated using handgrip strength and gait speed. Rectus femoris ultrasonography was performed, measuring muscle thickness (MT), cross-sectional area (CSA), pennation angle (PA), and echo intensity (EI). Body composition was analyzed using bioelectrical impedance analysis, and appendicular skeletal muscle mass (ASM) was estimated using a validated predictive equation. All participants had undergone dual-energy X-ray absorptiometry within the previous year, and FRAX scores were calculated. Results: Women with osteoporosis had significantly lower muscle thickness compared to controls after adjusting for age and BMI. Rectus femoris MT and CSA were significantly correlated with predicted ASM (r = 0.428, p < 0.01; r = 0.462, p < 0.01). The area under the curve (AUC) for MT in identifying low muscle mass was 0.732 (95% CI 0.601 to 0.862, p = 0.001) at a cut-off value of 1.38 cm. CSA had an AUC of 0.789 (95% CI 0.678 to 0.901, p < 0.001) at a cut-off value of 4.48 cm². CSA, MT, and PA were significant independent predictors of osteoporosis regardless of bone mineral density but not of FRAX parameters. Conclusions: Rectus femoris ultrasonography is a potentially reliable and rapid method for assessing muscle mass. Rectus femoris ultrasound parameters may serve as predictors of osteoporosis, independent of bone mineral density.