Usefulness of Ultrasound Shear Wave Elastography for Detection of Quadriceps Contracture in Immobilized Rats

Quadriceps contracture is an abnormal pathological shortening of the muscle-tendon unit. To improve the prognosis of quadriceps contracture, improvement of its diagnostic method is needed. In this study, we evaluated the diagnostic utility of ultrasound shear wave elastography in a rat model of quadriceps contracture induced by immobilization. Fifty Wistar rats were randomly divided into control and immobilization groups. During up to 4 weeks of joint immobilization, the quadriceps elastic modulus, muscle hardness, creatinine phosphokinase levels, joint range of motion, histopathologic parameters, and levels of fibrosis-associated mRNA expression were measured every week in the immobilization and control groups and compared. In the immobilization group, the elastic modulus gradually but significantly increased (p < 0.05) throughout the immobilization period. However, muscle hardness and serum creatinine phosphokinase levels only increased at 1 and 2 weeks after the start of immobilization, respectively. Muscle atrophy and shortening progressed throughout the immobilization group. Collagen type I and III, α-SMA protein, and mRNA expression of IL-1β and TGF-β1 significantly increased (p < 0.05) throughout in the immobilization group. Ultrasound shear wave elastography is the most useful method for clinical assessment of muscle contracture.