The effect of fibrin clot on healing rat supraspinatus tendon defects.

The possibility that fibrin clot, with its chemotactic and mitogenic factors, might improve the healing of a defect in the rat supraspinatus tendon was evaluated. Bilateral defects were surgically created in the rat supraspinatus tendon near the humeral insertion. One defect in each rat was filled with fibrin clot from a donor animal while the other side acted as a control. The tendons were evaluated at 3, 6, and 12 weeks. On histologic evaluation persistent defects were seen at all time points, whereas the healing tissue became less cellular with better collagen organization over time. Fibrin clot remained in the healing defects of treated shoulders at early time points. Biomechanically, there was improvement of properties over time, but they did not approach those of normal tendon by 12 weeks. There was no effect from addition of the fibrin clot except at 3 weeks, where it led to a decrease in material properties.