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.

Automated summary

Increasing knee flexion angle was found to increase certain mechanical properties of the vastus lateralis muscle, while the transverse shear modulus remained consistent. In a healthy volunteer, tensile anisotropy was found to be greater than shear anisotropy, indicating that these parameters are independent.