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A rat muscle contusion model created by a modified drop-mass method using ultrasound
Ryo Miyazaki1, Takashi Kanamoto1, Yujie Ren1
1Department of Health and Sport Sciences, Medicine for Sports and Performing Arts, The University of Osaka Graduate School of Medicine, Faculty of Medicine, Suita, Japan.
Bone & Joint Research
|July 1, 2026
Summary
This study establishes a reproducible ultrasound-guided muscle contusion model in rats. The model aids in screening molecules, like tissue kallikrein (KLK1), involved in muscle healing and scar formation.
Area of Science:
- Biomedical Engineering
- Regenerative Medicine
- Skeletal Muscle Research
Background:
- Muscle contusions often result in incomplete regeneration and excessive scarring, impairing functional recovery.
- Developing reproducible animal models is crucial for studying muscle healing and testing therapies.
- Existing models may lack the precision needed for detailed molecular investigation.
Purpose of the Study:
- To establish a reproducible skeletal muscle contusion model using a modified drop-mass method with ultrasound guidance.
- To investigate the feasibility of this model for molecular screening of muscle contusion healing.
- To identify key molecules involved in the muscle healing process.
Main Methods:
- A modified drop-mass method with ultrasound guidance was used to induce muscle contusions in 70 Wistar Hannover rats (68 included).
- Reproducibility was assessed via ultrasound imaging, histology, gene expression analysis (inflammation, macrophages), and muscle strength tests.
- RNA sequencing was employed for comprehensive genetic analysis to screen for healing-related molecules.
Main Results:
- Ultrasound revealed hypoechoic areas in injured muscles; cross-sectional area peaked at 24 hours post-injury.
- Histology showed progressive fibrous tissue formation from day 7 to day 14.
- Muscle strength decreased at 3 and 7 days post-injury; inflammation and macrophage markers were upregulated.
- RNA sequencing identified tissue kallikrein (KLK1) with increased expression on day 7 compared to day 3, confirmed by qPCR and immunohistochemistry.
Conclusions:
- A reproducible skeletal muscle contusion model was successfully established using an ultrasound-guided modified drop-mass technique.
- This model shows significant potential for the molecular screening and investigation of muscle contusion healing processes.
- Tissue kallikrein (KLK1) emerged as a molecule of interest in the later stages of muscle healing within this model.
