Factors Affecting in vivo SH and SV Mode Wave Propagation in vastus lateralis Muscle at Varying Knee Flexion Angles Using Ultrasonic Rotational 3D SWEI

We previously have demonstrated the use of ultrasonic rotational 3D SWEI to measure all three mechanical properties necessary to fully characterize the vastus lateralis muscle in vivo as an incompressible transversely isotropic material: transverse shear modulus
$\mu_{T}$
, longitudinal shear modulus
$\mu_{L}$
, and tensile anisotropy
$\chi_{E}$
. In this work we investigate how varying knee flexion angle affects the mechanical properties of the vastus lateralis. As knee flexion angle increased,
$\mu_{L},\ \chi_{E}$
, and
$\chi_{\mu}((\mu_{L}-\mu_{T})/\mu_{T})$
all increased, while
$\mu_{T}$
remained consistent across knee angles. At all nine knee flexion angles investigated in a healthy volunteer
$\chi_{E} > \chi_{\mu}$
, indicating that these are independent parameters.