Ultrasound method for estimating the cross-sectional area of the psoas major muscle

Purpose: The present study aimed to develop an ultrasonographic method for estimating the cross-sectional area of the psoas major muscle. Methods: The muscle cross-sectional area (CSAMRI) and thickness (MTMRI) of the psoas major muscle at L4-L5 on the right and left sides of the body were measured using magnetic resonance imaging in 11 healthy sedentary men age 21 to 25 yr. Ultrasonographic images were obtained at the corresponding sites where CSAMRI and MTMRI measurements were performed. From the ultrasonographic images, the thickness of the psoas major muscle (MTUS) was analyzed on both sides of the body. Results: The interclass correlation coefficient of MTUS measurements performed on two separated days was 0.951 for the right side and 0.971 for the left side. CSAMRI was significantly correlated to MTMRI (r = 0.934 for the right side and r = 0.910 for the left side). There was no significant difference between MTMRI (4.68 ± 0.39 cm for the right side and 4.73 ± 0.39 cm for the left side) and MTUS (4.67 ± 0.40 cm for the right side and 4.72 ± 0.43 cm for the left side). The MTUS was significantly correlated to MTMRI (r = 0.979 for the right side and r = 0.980 for the left side) and CSAMRI (r = 0.947 for the right side and r = 0.916 for the left side). Conclusion: The current results indicate that the psoas major muscle thickness determined by the ultrasonographic method is useful for estimating the cross-sectional area of the psoas major muscle.