Natural Healing of Anterior and Posterior Attachments of the Rabbit Meniscus

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Abstract
The natural healing capacity of the anterior or posterior medial meniscal attachment after radial transection and the effect of such procedures on knee joint cartilage were investigated in 28 skeletally mature New Zealand white rabbits. Either the anterior (n = 14) or the posterior attachment (n = 14) was radially transected in the right knee joint. Fifty percent of the rabbits with each procedure were euthanized at 6 weeks and 50% at 12 weeks. The histologic characteristics of the healing tissue were evaluated, including immunohistochemical demonstration of nerve fibers. Histologic changes in the synovium and articular cartilage were graded for severity and extent. The concentration of proteoglycan fragments in joint fluid was analyzed before operation and at euthanasia. After both procedures, the transected attachment healed in a prolongated position resulting in peripheral displacement of the meniscus. The healing tissue at 6 weeks was composed mainly of granular tissue. By 12 weeks, the healing tissue at the anterior attachment had a ligament like structure, but at the posterior attachment, fibrocartilage like tissue had formed. Nerve fibers were found in the healing tissue, but connections to nerves in normal attachment or meniscal tissues were not found. Increased concentrations of proteoglycan fragments, articular cartilage degeneration, and synovitis were found in the operated knees. These data indicate that although the meniscal attachment can heal in a prolongated position, such a meniscus has lost its mechanical functions. Further, a joint protective function of the neoneurons is doubtful because of the lack of continuity with the adjacent meniscus. Rigid fixation of the attachment seems essential for a functional meniscal substitute.