Tissue engineering of ligament and tendon healing.

Ligaments and tendons are bands of dense connective tissue that mediate normal joint movement and stability. Injury to these structures may result in significant joint dysfunction because they either heal by production of inferior matrix or do not heal at all. The process of ligament and tendon healing is complex and the roles of cellular and biochemical mediators continue to be elucidated. The expression of growth factors and growth factor receptors is modulated after injury, and cells from healing tissues are responsive to growth factors. Tissue engineering offers the potential to improve the quality of ligaments and tendons during the healing process. The concept is based on the manipulation of cellular and biochemical mediators to affect protein synthesis and improve tissue remodeling. Recently, novel techniques such as application of growth factors, gene transfer techniques, and cell therapy have shown promise and may become effective biologic therapies in the future. Many groups have been successful in introducing marker and therapeutic genes into ligaments and tendons. Cell therapy involves the introduction of mesenchymal progenitor cells as a pluripotent cell source into the healing environment. The combination of cell therapy with growth factor application via gene transfer offers new avenues to improve ligament and tendon healing.