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Vascular Response to Injury

The vascular supply of the meniscus is the essential element in determining its potential for repair. This blood supply must have the ability to support the inflammatory response characteristic of wound repair. Clinical and experimental observations have demonstrated that the peripheral meniscal blood supply is capable of producing a reparative response similar to that in other connective tissue.

Following injury within the peripheral vascular zone, a fibrin clot forms that is rich in inflammatory cells. Vessels from the perimeniscal capillary plexus proliferate through this fibrin “scaffold,” accompanied by the proliferation of undifferentiated mesenchymal cells.

Eventually, the lesion is filled with a cellular, fibrovascular granulation tissue that “glues” the wound edges together and appears to be continuous with the adjacent normal meniscal fibrocartilage. The initial strength of this repair tissue, as compared with the normal meniscus, is minimal. Increased collagen synthesis within the granulation tissue slowly results in a fibrous scar.

Experimental studies have shown that radial lesions of the meniscus, extending to the synovium, are completely healed with fibrovascular scar tissue by 10 weeks. Modulation of this scar into normal-appearing fibrocartilage, however, requires several months.

The initial strength of this repair tissue, as compared to the normal meniscus, has been found to be significantly decreased during this time (33% at 8 weeks, 52% at 4 months, and 62% at 6 months) . The ability of meniscal lesions to heal has provided the rationale for the repair of peripheral meniscal injuries, and many reports have demonstrated excellent results following primary repair of peripheral meniscal injuries. Follow-up examinations of these peripheral repairs have revealed a process of repair similar to that noted in the experimental models.

When examining injured menisci for potential repair, lesions are often classified by the location of the tear relative to the blood supply of the meniscus and the “vascular appearance” of the peripheral and central surfaces of the tear. The so-called red-red tear (peripheral capsular detachment) has a functional blood supply of the capsular and meniscal side of the lesion and obviously has the best prognosis for healing.

The red-white tears (meniscus tears through the peripheral vascular zone) have an active peripheral blood supply; however, the central (inner) surface of the lesion is devoid of functioning vessels. These lesions have sufficient vascularity to heal by the aforementioned fibrovascular proliferation.

The white-white tears (meniscus lesions completely in the avascular zone) are without blood supply and theoretically cannot heal (77). In an effort to “extend” the level of repair into these avascular areas, techniques such as synovial abrasion, fibrin clot placement, and vascular access channels have been developed to attempt to provide vascularity to these white-white tears.

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