Cell, matrix changes and alpha-smooth muscle actin expression in repair ofthe canine meniscus

Processes in the repair of a crevice in the knee joint meniscus were invest igated in 10 dogs. Two 2-mm cylindrical plugs from each medial meniscus wer e removed, rendered acellular by freezing and thawing, and then reinserted into the meniscus. Dogs were euthanized at intervals of 3-52 weeks after su rgery. The crevice between the plug and meniscus at 3 weeks after surgery w as filled with a tissue containing a-smooth muscle actin-positive cells. On e year aft er surgery, the plug had remodeled and was populated with spindl e-shaped and fibrochondrocyte-like cells. The plug had an appearance interm ediate between that of hyaline and fibrocartilage at this time, with a seam less integration in sites between the remodeled plug and the surrounding me niscus, a-smooth muscle actin-positive cells were concentrated at the inter face of the remodeled plug and adjacent meniscus and at the surface of the plug. Therefore, remodeling of both the plug and meniscal tissue and the pa rticipation of a-smooth muscle actin-positive cells appear essential for in tegration of the plug into the adjacent meniscal tissue. Cells in the super ficial zone of the meniscus seem to be active in the repair process. A chan ge in both the phenotype of the cells and the quality of the matrix toward a more hyaline state appears to be an integral part of the remodeling proce ss in the meniscus.