AAOS 2004: All About Allografts -- Select Highlights of the 71st Annual Meeting of the American Academy of Orthopaedic Surgeons

March 10-14, 2004; San Francisco, California

Donald Johnson, MD

Disclosures
In This Article

Overview of Advances in Allografts: Presentation Summary

The papers reviewed below, from the 71st Annual Meeting of the AAOS, outline the utility of allografts in orthopaedic medicine.

In light of the recent infections after ACL reconstruction with allograft tissue, this paper reported on the Clearant technology, which is aimed at the terminal sterilization of soft tissue grafts. This proprietary process radiates the soft tissue grafts in a fluid medium with a high dose of gamma radiation of 5O mrad or 50 cKy. The purpose of this paper was to answer the key question of whether there was significant weakening of the graft with radiation in the fluid medium. The study compared tibialis tendons, with no radiation, with 18 kGy conventional radiation, with 50 cKy controlled radiation, and with 50 cKy radiation with fluid medium protection. The results showed that there was no reduction in the biomechanical properties of the graft when radiated in the fluid-protected medium. This terminal sterilization killed clostridium and viruses. There is some concern that the fluid medium, which contains DMSO, ethylene glycol, and other chemicals, may produce some long-term deleterious effect in the knee or in the graft. The unhappy outcome of the ethylene oxide sterilization of grafts is too recent in our memory.[8] The authors also reported on the short-term follow-up of Achilles tendon allograft ACL reconstruction. The short-term follow up was satisfactory. CryoLife, Inc., has decided to make this the process for the terminal sterilization of their soft tissue grafts.

The purpose of this paper was to review the clinical results of 40 meniscal transplants, and in particular to examine the appearance of the transplant under loaded conditions. The clinical results showed that preoperatively, 77% of patients had pain with daily activities, but after the transplantation, only 7% had pain with daily activities. Four of the transplants failed early. On MRI, the grafts showed no difference on the loaded situation compared with normal meniscus. Some of these patients had an associated osteochondral autogenous transfer procedure. How do you decide if the arthritis is too advanced for meniscal transplantation? If there is 30% of exposed bone, more than 1 mm of narrowing or flattening on the femoral condyle, then this is a graded as a severe situation and is a contraindication to transplantation. This study did not answer the question of prevention of late osteoarthritis, but did show that in the short term, the pain was relieved in most patients, and their activity level was increased. In follow-up, 77% of the patients were able to return to light recreational activities. This study had ACL reconstructions and osteochondral autologous transfer system (OATS) procedures as well, and no multivariate analysis was done to take this into account.

In this paper, William Bugbee, MD, from the University of California, San Diego, reported on his experience with fresh allografts for avascular necrosis (AVN) of the femoral condyle of the knee. Most of these patients who were grafted (95%) had steroid-induced osteonecrosis of the knee, in one or both of the femur condyles. Fresh allografts were used that were less than 7 days old. Fixation of the graft was with absorbable pins. No weight bearing was advised for 3 months. There were 18 patients with AVN of either or both of the medial or lateral femoral condyles. The results showed that 13 of 14 had improved knee function at follow-up of 3.8 to 7.5 years. Five of the 14 patients died from their disease, leukemia. The patients had leukemia and AVN but were not transplanted until they were 5 years out from the onset of their disease. Other patients had the AVN as the result of steroid treatment for asthma or lupus. These results should be compared with the core decompression procedure that had a 27% reoperation rate. Total knee replacement has good outcome after failed allografting.

The authors feel that this is an acceptable alternative for younger patients with AVN due to cancer treatment and steroid use. In the retrievals that were done, the graft to the host shows variable healing, with chondrocytes present. Large grafts may have immunogenicity problems. The grafts must be fresh, as at 3 weeks there is only 70% cell variability.

Toronto and San Diego are the only 2 locales in the country in which physicians use fresh frozen osteochondral grafts within 7 days. The question is: can other centers match the results reported by Drs. Gross and Bugbee? The commercial grafts that are available are stored by immediate freezing for up to 42 days. What happens to the cellular viability of the grafts that are frozen for longer periods of time? In this study, osteochondral plugs were harvested from sheep and cold stored for 1, 17, and 42 days. They were then implanted into the distal femur of sheep. The sheep were sacrificed at 4 and 6 weeks after allograft transplantation. The results showed that at 17 days of storage, there is a 26% decrease in chondrocyte viability; and at 42 days of storage, there is a 48% decrease in chondrocyte viability. The authors noted that the biomechanical properties also reduced over time. The material properties did not improve after the transplantation. The conclusion of this group of investigators was that cold storage adversely affected the material properties of the osteochondral grafts.

The premise of this paper was that the ABO antigens that are present on the graft could produce an immunologic response, compromising the outcome of the transplantation. In this study, the authors retrospectively matched the blood type of the graft with the blood type of the patient. The failures of the grafts were examined, comparing the mismatched blood type. The authors found that in the matched blood type, the success rate was 86%, compared with a success rate of 72% in the unmatched blood type.

The conclusion of this study was that the effect of ABO blood type may have a clinical effect on the outcome of fresh allografts. The authors suggested that the graft may need to be cleansed to reduce the antigen load, and that the blood type of the recipient should be matched to the donor.

In this presentation, Frank Noyes, MD, from the Cincinnati Sportsmedicine Research and Education Foundation, Cincinnati, Ohio, provided an overview of his experience with allografts in ACL reconstruction. He reviewed allografts from the perspective of their biomechanics, healing, remodeling, the potential for disease transmission, the scientific basis for selection, and the comparative clinical studies of allografts.

Biomechanical studies in animals have shown that it takes a prolonged time to regain the strength of the allograft, and it may remain at 50% below normal. The grafts show similar histologic remodeling to autografts, but have been shown to have delayed cellular repopulation, incomplete replacement of the graft with scar, and consequently below normal mechanical properties. There may be low-grade immunogenicity, but this does not seem to affect the clinical outcome.

The potential for disease transmission with allograft transplantation remains a problem as there is no standardized terminal sterilization process.

Is there any scientific basis for selecting allografts over autografts? There have been several studies[11,29] that showed there is no significant difference in pain, range of motion, complications, patellofemoral crepitus, arthrofibrosis, or quadriceps strength. These are all the reasons cited to use allografts over autografts, but there is no difference when compared in a randomized trial.

There is a case to be made to use allografts in the dislocated knee, when multiple grafts are required to reconstruct all the injured ligaments. In general, allografts are used less frequently due to cost and potential for disease transmission, and most authors feel that the use of allografts are not justified for primary ACL reconstruction.[30] The allografts do have equal results compared with the autograft when used in the acute situation. The knee stability is maintained over the long term with allografts.[15]

In a review of the authors' experience, they had better success with autograft quadriceps tendon for revision ACL reconstruction compared with allograft.[31,32,33] The allograft had a tendency toward an increased failure rate in chronic knees.[32]

The summary by Noyes and colleagues noted that practitioners using allografts for ACL reconstruction should be somewhat circumspect in their approach; however, good results can be obtained in the acute setting.

Dr. Noyes suggested that the clinician should apply the Scott Dye family test when considering allografts. "Would you put an allograft in your daughter?"

I agree with Dr. Noyes and do not feel that allografts are indicated for primary ACL reconstruction.[30]

Walter Shelton, MD, from Mississippi Sports Medicine and Orthopaedic Center, Jackson, Mississippi, presented an overview of the current status of meniscal allografts. These have been in use for 20 years, and approximately 3410 cryopreserved grafts have been implanted by 465 surgeons. The use of the cryopreserved grafts has decreased in the past couple of years because of concerns about infections and cost. The graft is known to be effective in reducing pain in the young patient after total menisectomy. The graft seems to be durable, with a 75% success rate at 5 years for medial transplants, and an 85% success rate for lateral transplants. The medial technique is done with 2 separate bone plugs secured in tunnels, whereas the lateral is done with a slot of bone placed in a keyed groove in the lateral tibial plateau. It is important that the graft be implanted in the early stages of arthritic degeneration, with relatively normal limb alignment. The question of whether these grafts are successful in preventing late degenerative changes has not been answered by the current studies.

Alan Barber, MD, from Plano Orthopaedic and Sports Medicine, Plano, Texas, outlined the current status of osteochondral transfer for localized chondral defects in the knee. The indication for grafting is a full-thickness cartilage defect in a stable knee with no generalized arthritis. Autografts are indicated for small defects 1-2.5 cm in size, and allografts are indicated for larger defects > 2.5 cm.

The autograft technique is by multiple small plugs taken from the intercondylar notch of the same knee and transferred to the defect in the femoral condyle. The allograft is generally a large shell graft taken from a matched region of the condyle as the recipient. The literature shows good long-term results of the allograft transfer.[25]

Dr. Gross[34] reported on 126 femoral grafts with 7.5 years of follow-up. The survivorship analysis showed 95% success at 5 years, 71% at 10 years, and 66% at 20 years. The tibial grafts did not fare as well, with 95% at 5 years, 80% at 10 years, 65% at 15 years, and 46% at 20 years.

In addition, Dr. Bugbee[35] noted an 84% overall success rate in 211 patients followed over 4 years. The femoral grafts performed the best, achieving a 93% success rate, patellofemoral grafts achieved a 78% success rate, and tibial grafts were 65% successful -- excellent results for this technique.

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