Cross-Sectional Nakagami Images in Passive Stretches Reveal Damage of Injured Muscles

Abstract

Muscle strain is still awanting a noninvasive quantitatively diagnosis tool. High frequency ultrasound (HFU) improves image resolution for monitoring changes of tissue structures, but the biomechanical factors may influence ultrasonography during injury detection. We aim to illustrate the ultrasonic parameters to present the histological damage of overstretched muscle with the consideration of biomechanical factors. Gastrocnemius muscles from mice were assembled and ex vivo passive stretching was performed before or after injury. After injury, the muscle significantly decreased mechanical strength. Ultrasonic images were obtained by HFU at different deformations to scan in cross and longitudinal orientations of muscle. The ultrasonography was quantified by echogenicity and Nakagami parameters (NP) for structural evaluation and correlated with histological results. The injured muscle at its original length exhibited decreased echogenicity and NP from HFU images. Cross-sectional ultrasonography revealed a loss of correlation between NP and passive muscle stretching that suggested a special scatterer pattern in the cross section of injured muscle. The independence of NP during passive stretching of injured muscle was confirmed by histological findings in ruptured collagen fibers, decreased muscle density, and increased intermuscular fiber space. Thus, HFU analysis of NP in cross section represents muscle injury that may benefit the clinical diagnosis.

Stretch-Induced Healing of Injured Muscles Is Associated With Myogenesis and Decreased Fibrosis

“…Decreased NPI values of the longitudinal gastrocnemius muscle after overstretched injury were observed in an ex vivo mice model. 18 Similar findings have been identified in our rat model of injured muscles. Disordered skeletal muscle tissue organization after injury could contribute to inhomogeneous changes of the echo amplitude distribution.…”

“…The present study aimed to explore the effects of mechanical stretch on myogenic lineage proteins and skeletal muscle fibrous tissue histology in a rat model of muscle injury. Ultrasonic Nakagami parametric imaging, a useful and reliable tool to monitor muscle morphology, 18,33 was used to monitor muscle healing after injury in the present study. The anticipated findings regarding the stretch-induced muscle healing process may provide insights into the clinical application of therapeutic stretching exercises on patients with muscle injuries.…”