At the “Empirical Answers to Burning Clinical Questions” workshop during the 2015 American Orthopaedic Society for Sports Medicine (AOSSM) annual meeting, Rick W. Wright, MD, of Washington University School of Medicine, took on the oft-discussed issue of outcomes for allograft versus autograft for anterior cruciate ligament (ACL) reconstruction.
Presenting himself as “not really pro-autograft or pro-allograft,” Dr. Wright stressed that there may not be “one definitive answer, because it depends on the situation.” Factors such as the patient’s age, participation in sport, position played, or occupation can affect the decision of which type of graft to use.
The goals of any graft, according to Dr. Wright, are accurate reproduction of the anatomy and biomechanics of the ACL, rapid incorporation with reasonable initial fixation, and, in the case of an autograft, low graft site morbidity. He noted the differing characteristics between allografts and autografts particularly the three primary autograft types—bone-patellar tendon-bone (BPTB) (Fig. 1), hamstring, and quadriceps tendon with or without bone. He also outlined the following primary outcomes and measures:
- graft rupture
- structural measures (such as the KT1000)
- return to sport
- patient-reported outcomes
- patient satisfaction
“Often our discussion of ACL grafts and graft choices is focused on failure, but that is just part of the equation,” he said.
Personally, Dr. Wright said, “If the patient is younger than age 35, I will do a BPTB. But some patients want a hamstring graft, and about 25 percent of my grafts are hamstring. If the patient is older than age 40, an allograft is always discussed as an option.” In revision ACL surgery, Dr. Wright uses autograft if at all possible.
“I became much more dogmatic about using an autograft for ACL revisions based on the evidence from the MARS (Multi-Center ACL Revision Study) graft choice study published last year,” he admitted. “Prior to that I wasn’t really sure that allograft wasn’t as good. But it appears that autograft is a little better in revisions.”
Counting all costs
Dr. Wright surveyed various studies examining costs of autograft and allograft. A comparison of BPTB autograft versus Achilles allograft reported a mean hospital charge of $5,695 for the autograft versus $4,622 for the allograft (P < 0.0001). He noted, however, that the study did not control for hospitalization, and “many more of the autograft patients were hospitalized.”
Another study compared total hospital costs for hamstring autograft ($4,072) versus anterior tibialis allograft ($5,195). “The increased costs of the allograft were not offset by decreased operating room and recovery room time,” said Dr. Wright.
In a comparison involving outpatient procedures, the mean total cost for allograft reconstruction was $5,465 versus $4,872 for autograft.
On cost, Dr. Wright concluded, “Cost typically favors the autograft, but as we know, reimbursement and up-charge for the allograft can vary and can affect the equation. With no clear-cut answer, as we move toward bundled payments, this issue will probably go away.” He also noted that decision tree analysis will sometimes point to allograft as offering the best potential for decreased pain and complications.
For outcomes, many measures
Dr. Wright surveyed some of the outcome descriptors for ACL grafts. For proprioception—specifically, passive motion detection and joint position sense—a comparison of allograft, autograft, and ACL-deficient knees found no real difference between the two graft patient groups.
In regard to infection, Dr. Wright referenced a retrospective analysis of 3,126 ACL reconstructions. Of 18 overall infections, 6 were in the allograft group (0.44 percent), 7 in the BPTB autograft group (0.49 percent), and 5 were in the hamstring autograft group (1.44 percent). Dr. Wright noted that although allograft and BPTB autograft were “fundamentally the same,” hamstring autograft had an elevated risk of infection. “It’s hard to know why that was happening,” he said.
A systematic review of 20 studies using the International Knee Documentation Committee (IKDC) standards for stability (2 mm laxity = normal; greater than 5 mm laxity = abnormal) found that autografts were more favorable than allografts for normal stability (P < 0.01). Autografts also had lower rates of abnormal laxity (P < 0.01).
As for failure rates, Dr. Wright noted that one meta-analysis found a 5.03 odds ratio for increased rupture with allograft. When allografts that were irradiated or prepared with chemical agents were removed, however, the difference was not so marked.
In a Multicenter Orthopaedics Outcomes Network (MOON) study—one that Dr. Wright said has caused “many of the MOON members to change their behavior”—the focus was on failure rates of allograft and autograft at 2 years. Researchers plugged patient age and activity into a nomogram and found that at any age, allograft has an approximately four times greater risk of rupture. For every 10-year reduction in age, the risk of rupture increased 2.3 times. Thus, a 15-year-old will have a 2.3-times greater risk of ACL tear over that of a 25-year-old.
By way of example, the nomogram indicated that a 14-year-old female athlete would have a 22 percent risk for failure with allograft and a 5.6 percent risk with autograft at 2 years. In a 40-year-old male, the risk would be 2.6 percent with allograft and 0.6 percent with autograft.
Although these findings seem to point to use of autograft as a rule in younger patients, a recent study of patients younger than age 25 found a lower rate of failure with allografts. The study involved 28 patients with BPTB allografts and 53 patients with BPTB autografts. At 2-year follow-up, the patients had equal activity scores, with fairly high levels of activity. Of the seven failures, two were allografts (7.1 percent) and five were autografts (9.4 percent).
However, a randomized controlled trial comparing hamstring autograft with fresh frozen nonirradiated posterior tibialis allograft came to a different conclusion. The study involved 99 patients (100 knees), 95 of whom were active-duty military. At 10-year follow-up, among the 97 knees available, the graft failure rate was 8.3 percent in in the autograft group and 26.5 percent in the allograft group.
In summary, Dr. Wright noted the recent proliferation of systematic reviews comparing graft choices and joshingly called for “a stop to the systematic review/meta-analysis madness.” “When we’ve done 10 in the last 3 or 4 years, we can take a few months off,” he observed.
The data, he noted, are plentiful, but “ultimately are confusing due to poor control of a variety of factors in even well-intentioned studies. When you read these studies, you have to figure out the age and activity of the patient, and the handling of the allograft. I think anyone here will probably think that an allograft has a little bit higher chance of failure. But that is not the only outcome to consider.”
For information on the speaker’s potential conflicts of interest, visit www.aaos.org/disclosure
Terry Stanton is a senior science writer for AAOS Now. He can be reached at firstname.lastname@example.org
- Major considerations in graft choice include those related to safety (in allograft, biologic safety; in autograft, harvest complications), economics, and outcomes and failure rates.
- Infection rates for both BPTB allograft and autograft are roughly the same, with a somewhat elevated rate observed for hamstring autograft.
- Study results appear to favor autograft over allograft by measures of stability and abnormal laxity.
- Higher reported failure rates for allograft may be influenced by inclusion of irradiated/chemically treated grafts in the data analysis.
- In studies of younger patients, autograft had a markedly lower failure rate than allograft, but in patients 40 or older, allograft may have a success rate of approximately 97 percent and should be viewed as an option.
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