Results of Animal Research Using Anterior Cruciate Ligament and Medial Meniscal Allografts

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SummaryResults of most anterior cruciate ligament (ACL) and meniscal allograft studies have been encouraging and have showed good potential for clinical application. However, the number of variables among studies and the fact that they are few in number made the development of conclusions difficult. With ACL allografts, most studies have used frozen bone-ACL-bone allografts in a dog model. Other graft tissues have included bone-patellar, tendon-bone, patellar-tendon strips, flexor tendons, and fascia lata; other preservation methods used have been cryopreservation and freeze-drying with ethylene oxide. Goats, sheep and primates have been some of the animal models used. Clinical, radiographic, gross pathological, histological, and mechanical evaluations have shown similar findings between allografts and autografts. This favorable comparison has been qualified in some studies with concerns that allografts have had more variable results, have healed more slowly, and have maintained less normal mechanical properties. Results have been more variable and complications greater with bone-ACL-bone grafts in dogs. Negative results in a few studies have been associated with an immune response. With medial meniscal allografts, most studies have used frozen or cryopreserved grafts in dogs. Other animal models have included the goat, sheep, and rabbit, and other preservation methods have included tissue-culture media, glutaraldehyde, and lyophilization with -v-radiation. Glutaraldehyde-treated grafts excepted, results have been generally good, regardless of the method of preservation, animal model, or other variables. Allografts have usually healed rapidly to surrounding tissue without evidence of inflammation related to an immune response. However, revitalization of the central core of the graft has not been complete at 12 months. Cryopreservation has allowed implantation of viable cells (10%) but benefits from live donor cells are not clear. Differences between cryopreserved and frozen menisci have been minimal. Autografts and allografts have had similar gross changes (i.e., shrinkage and loss of normal C-shape). Mild focal cartilage damage has occurred in areas exposed by the altered menisci. Additional studies are needed to define the best method of preservation and sterilization, the best allograft tissue, the ideal surgical technique for implantation, the role of immunological reactions, and long-term results.

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