Meniscal repair using the outside-to-inside technique.

Research during the past decade has elucidated the structure and function of the knee joint meniscus, and both clinical and experimental studies have demonstrated the importance of this structure. Recent advances, such as the use of an exogenous fibrin clot, have allowed preservation of an increasingly greater proportion of injured menisci. The success of these methods will be established only by long-term follow-up studies demonstrating a lower incidence of progression to degenerative joint disease. It is hoped that an increasing understanding meniscal fibrochondrocytes biology and response to injury will result in the development of novel therapeutic strategies for repair of the injured meniscus. Basic studies clearly have demonstrated that meniscal fibrochondrocytes possess intrinsic repair capability. Both in vitro cell culture studies and in vivo animal models have provided the basic scientific foundation for the use of fibrin clot in tears in the avascular portion of the meniscus. The use of fibrin clot has allowed further expansion of the proportion of meniscal tears that are potentially reparable. Tears in the central, avascular zone of the meniscus, formerly thought to be irreparable, now may undergo repair with an enhanced opportunity for healing. The factors associated with a good prognosis in the meniscal repair include acute tear; peripheral tear; a stable knee; and the presence of serum or factors derived from serum, such as the presence of a fibrin clot, or vascular access channel, or hemarthrosis. Cell culture and molecular biologic techniques currently are being used to improve our understanding of meniscal biology. Particular challenges for future research include determination of the source of the reparative cells in meniscal repair, exploration of the biomechanical properties of the reparative tissue, and demonstration of the potential use of growth factors in meniscal healing. A further potential use of fibrin clot in the future is as a carrier vehicle both for the delivery of growth factors to injured meniscal and for the transplantation of autogenous fibrochondrocytes in meniscal defects. Other avenues of investigation include the use of cytokines to enhance meniscal healing, studies of meniscal replacement with allografts and collagen-based prostheses for meniscal regeneration, and the potential to augment meniscal cell proliferation and matrix synthesis by gene therapy techniques.