Age dependent repair of muscle rupture. A histological and microangiographical study in rats.

Healing of contusion injury in the gastrocnemius muscle was studied in young adult and old rats. A standard blunt muscle contusion was induced to the left calf of each animal and studied histologically and microangiographically 2-21 days after the injury. The inflammatory cell reaction was more intense, the haematoma was larger and the proliferation of fibroblasts and production of collagen scar more pronounced in the young rats. The sprouting of new capillaries and regeneration of ruptured muscle fibres occurred more rapidly and intensively in the young animals, and the resorption of haematoma and phagocytosis of necrotic tissue occurred later in the old rats. The decreased repairing capacity in muscles of older animals resembles that seen earlier in immobilized muscles of adult rats, indicating that the response to the stimulus of injury decreases with advancing age.