Flexor tendon healing in the rat: A histologic and gene expression study

Purpose: To establish a rat flexor tendon laceration and repair model to investigate the molecular mechanisms of flexor tendon healing. Methods: Surgery was performed on rat flexor digitorum longus-tendons from both hind feet. Repaired tendons were harvested at 0, 3, 7, 14, 21, 28, 42, 56, and 84 days after surgery. Histologic study (first 84 days) and gene expression study (first 28 days) of several collagens and matrix metalloproteinases (MMPs) were performed. Results: In the histologic study pre-existing collagen bundles were degraded between days 7 to 21. Newly formed collagen fibers crossed the repair site by day 28. Remodeling of the collagen fibers continued until day 84. Gene expression of type I collagen decreased initially and then returned gradually to the initial level by day 28, whereas expression levels of types III, V, and XII collagen were increased after surgery. The expression levels of MMP-9 and MMP-13 peaked between days 7 to 14, whereas MMP-2, MMP-3 and MMP-14 levels increased after surgery and maintained high levels until day 28. Conclusions: The rat tendon laceration model represented the entire tendon healing process. The results of this study suggest that MMP-9 and MMP-13 participate only in collagen degradation, whereas MMP-2, MMP-3, and MMP-14 participate not only in collagen degradation but also in collagen remodeling. Copyright (C) 2003 by the American Society for Surgery of the Hand.