Extracellular matrix changes following blunt trauma to rat skeletal muscles.

Myofiber injury-repair was studied in the rat following blunt trauma to the lower leg in order to understand how the inflammatory and regenerative responses of muscles are altered when myofiber rupture is accompanied by bleeding and clotting reactions. A contusion injury to the muscles of the lower hindlimb of the rat was induced by applying an impact force of 4.7 N-m/cm2 to one leg. The gastrocnemius and soleus muscles were removed bilaterally and evaluated by histochemical and immunohistochemical techniques to document myofiber, vascular, and connective tissue alterations for several days following insult (6-120 hr). A significant increase in wet weight of the gastrocnemius muscle was noted 24 hr postinjury as fluid accumulation and bruising were evident in the muscles resulting from bleeding and inflammation. Vascular disruption was confirmed by the localization of some plasma constituents (fibrinogen, albumin, and complement C3) throughout the interstitial space and even inside some of the damaged myofibers. Inflammation was present and persisted for 5 days as evidenced by continued mast cell degranulation and increased vascular permeability. Using antibodies to identify specific proteoglycans which appear or disappear at various times during muscle regeneration, muscle repair could be followed. The repair process required approximately 10 days for restoration of morphologically intact myofibers. Thus, myofiber repair processes appear to be maintained even after disruption of the vascular system and ischemia following blunt trauma.