Allografts
The clinical data of both humans and animals have suggested that, as with autograft tissues, the allograft tissue revascularizes and becomes viable after implantation.[12,13,22] However, the rate of graft incorporation and remodeling are slower for allograft than for autograft.[12] Clinical studies with 5-year and 7-year follow-up have demonstrated that the outcomes of early ACL allograft reconstructions are similar to those of the autografts.[10,28] The incidence of chronic knee effusion after allograft reconstruction diminishes. This is perhaps because of the improved allograft procurement and avoidance of ethylene oxide sterilization in the new tissue preparation technologies.[10,28]
A variety of tendon allografts such as bone-patellar tendon-bone, Achilles tendon, anterior tibialis, fascia lata, and hamstring tendons have been used for ACL reconstructive surgery.[17]
Allografts have been widely used in adult ACL reconstruction with acceptable outcome. Noyes et al.[18] showed 89% excellent or good results using patellar tendon and fascia lata allografts in 47 patients. Allograft bone-patellar tendon-bone also has shown similar results in both short-term and long-term studies.[19]
The allograft tendons offer the advantage of no donor site morbidity; however, limitation of their supply and their high cost often is prohibitive.[28] Allograft reconstruction of the ACL has been shown to be significantly more expensive than autograft reconstruction.[18] There is concern for disease transmission as well as long-term viability.[21] However, arthroscopic evaluation of ACL reconstructed knees using allograft has revealed that the tendons maintain their structure and show no biodegradation up to 59 months after reconstruction.[12] Allograft tissue carries the risk of transmitting bacterial and viral diseases, including human immunodeficiency virus (HIV) and hepatitis. Although the risk of transmission has substantially diminished because of modern screening and tissue preparation technologies, the present concern about transmission of viral disease has not been fully resolved.[13] The risk of implanting an allograft from an HIV-infected donor has been reduced to one in more than 1 million.[17,24] Allografts have been shown to have similar biomechanical properties to autografts, although some of the sterilization techniques have been shown to decrease the graft strength, and this has been implicated in the failure of grafts.[13,23] Recent methods such as low-dose gamma irradiation have been shown to be safe for sterilization of ACL soft-tissue allograft, without compromising the biomechanical performance of the graft at early time points in rabbits.[29]
Application of allograft avoids using autogenous tissue, and for this reason the decreased graft site morbidity can lead to less postoperative and long-term pain.[13,30] It has been shown that the final outcome of patients who underwent ACL reconstruction using allograft was fairly similar to those of autografts.[12] On the other hand, it also has been shown that the healing process of the patients who received allografts was lower than those of autografts. There are some evidences that revascularization and replacement by host cells and collagen fibers takes longer for allografts than for autogenous grafts, which suggests that prolonged protection of the knee may be advisable after an allograft procedure.[13] For these reasons, allograft could be considered suitable graft material for skeletally immature patients because their healing response is faster.[21] Andrews et al.[30] reported the outcomes of eight patients who had reconstruction with fascia lata or Achilles tendon allograft through a transphyseal tibial drill-hole and an over-the-top position on the femur. No patients reported giving way, and four patients returned to their preinjury level of athletics.
Curr Orthop Pract. 2013;24(3):321-333. © 2013 Lippincott Williams & Wilkins
