Abstract: Objection To investigate the time-dependent appearance of circulating fibrocytes of skeletal muscle in rats after contusion. Methods The model of skeletal muscle wound was established in rat. The circulating fibrocytes in contused skeletal muscle were detected by CD45 and procollagen Ⅰ double immunofluorescence staining method. Results In the control group, CD45- and procollagen Ⅰ-positive cells were not detected in skeletal muscle. A few CD45 cells were observed aged from 6 h to 1 d after contusion. A few CD45- and procollagen Ⅰ-positive cells（fibrocytes） initially gathered in injury area 3 d after injury. The ratio of positive fibrocytes significantly increased 5 d after injury. The ratio of fibrocytes was highest at 7 d after contusion and then decreased. The volume of fibrocytes showed bigger with injury time increase compared with 3 d group. The expression of procollagen Ⅰ and CD45 were weakened at 14 d after injury. Conclusion The circulating fibrocytes are detected in contused skeletal muscle in time-dependent pattern. Circulating fibrocytes may be a marker in the wound age determination for contused skeletal muscle.

Key words: forensic pathology, wounds and injuries, muscle, skeletal, fibrocyte, wound age, rats