The location of the tear (in the vascular or avascular zone) plays a large role in the decision whether to repair or excise a torn piece of meniscus.
Vascularized tears are located in the periphery of the meniscus and have a functional blood supply that can provide fibrin clot and cells to populate the scar area. In animal models, radial tears, which extend from the avascular inner edge of the meniscus to the blood-rich synovium and capsule, heal with fibrovascular scar.7 In humans, tears in this region may have potential to heal but need to be stabilized surgically first. Often, these are repaired with sutures or bioresorbable arrows to immobilize the torn area and allow healing to occur.
Tears fully within the inner edge of the meniscus are avascular and have been shown to be incapable of healing even when they are stabilized with simple repair. Therefore, these tears are typically treated with removal of the torn tissue. The tears in the middle of the meniscus are sometimes capable of heal- ing, and therefore repair with additional techniques to stimulate healing (such as the creation of “vascular access channels” or the placement of fibrin clot into the tear before repair) is attempted, especially in young patients.
One of the goals of treatment is to pre- serve as much of the meniscal tissue as pos- sible. As noted, the meniscus serves as a shock absorber of the knee. Complete excsion of the meniscus results in a decrease in the load transmission area of approximately 50%; not surprisingly, the long-term results of total meniscectomy demonstrate an accel- eration of osteoarthritis of the knee. How- ever, when the torn tissue is so damaged that it can no longer function and, moreover, can create symptoms of catching or pain, menis- cal resection may be the best option.
Techniques of meniscal replacement with allograft or synthetic materials are also being developed. Allograft menisci are fastened to the knee capsule with sutures. It is thought that the initially acellular allograft is repopulated with cells, at least in the superficial regions of the allograft.8 Allograft transplantation is complicated by an immune response directed against the allograft meniscus, as shown in histologic studies of biopsies of pre- viously implanted allograft menisci.