Autograft or Allograft for ACL Reconstruction?

Careful graft selection plays key role in ACL reconstruction outcomes
Jennie McKee
Whether to use an autograft or an allograft in anterior cruciate ligament (ACL) reconstruction is still controversial. Although patella tendon autograft has long been considered the gold standard, allograft safety has improved significantly in the last 15 years, making it a viable option in some patients, according to Mark D. Miller, MD, who reported on the latest information on autograft and allograft tissue and offered tips on selecting an allograft tissue bank during the 2012 Arthroscopy Association of North America Specialty Day Program.

Commonly used allografts include (top to bottom): Achilles tendon, tibialis anterior, and semitendinosus (after preparation).
Courtesy of Mark D. Miller, MD

Autograft tissue
Autograft options include central one-third patellar tendon, quadrupled hamstring tendons, and quadriceps tendon (with or without bone block).
“In some studies, patella tendon autograft has been found to be slightly more stable than hamstring grafts,” said Dr. Miller. “It has strong initial fixation, but some studies have found an increased incidence of kneeling pain in patients, and some morbidity risks are associated with harvesting the patella tendon.”
According to Dr. Miller, a quadrupled hamstring autograft may represent a new gold standard, or join the patella tendon autograft as a “co–gold standard.”
“Quadrupled hamstring grafts have less harvest site morbidity than other types of autograft, but the saphenous nerve branches can be injured during harvest, and there is some postoperative weakness with deep knee flexion,” he said. “Quadrupled hamstring grafts also have slightly less stability than patella tendon grafts in some studies.”
He added that recent data suggest that quadrupled hamstring grafts smaller than 8 mm have increased failure rates.
“Concern about smaller grafts has led some surgeons to use an extra semitendinosus allograft, creating a six-strand hybrid autograft-allograft, or to triple the semitendinosus autograft, if it is long enough, to create a five-strand autograft,” he said.

Intraoperative photograph of posterior mini-incision hamstring harvest technique.
Reproduced from Prodromos CC, Fu FH, Howell SM, Johnson DH, Lawhorn K: Controversies in Soft-tissue Anterior Cruciate Ligament Reconstruction: Grafts, Bundles, Tunnels, Fixation, and Harvest. J Am Acad Orthop Surg 2008; 16:376-384.

Another option is the quadriceps tendon graft, which can be used with or without a bone block. This is a strong graft, noted Dr. Miller, with “surprisingly little morbidity.”
“Quadriceps tendon grafts can be dissected in layers, but cosmesis may be an issue,” he said.
Allograft tissue
Allograft options include the patellar tendon and the Achilles tendon, which are available with bone blocks. Soft tissue–only allografts include the semitendinosus, tibialis anterior, tibialis posterior, peroneus longus, and iliotibial band allografts.
“Using an allograft avoids the issue of harvest site morbidity,” he said. “Allograft use also results in slightly less loss of motion and requires less surgical time. In my experience, allografts are useful for complex cases, such as those involving multiple ligament injuries and revisions.”
But allografts have some disadvantages, including cost, availability, immune response, bacterial infection risk, and delayed graft incorporation/failure.
“Immune response and bacterial infection risk may be diminished by modern allograft processing techniques and shorter surgical times,” he said, adding that the smaller incision required with allograft tissue may also reduce the risk of bacterial infection.
“Viral infection risk may be offset by better donor screening and allograft disinfection techniques,” he added.
“Perhaps the most concerning disadvantage is an alarmingly high failure rate in young, active patients,” said Dr. Miller. “Recent studies have raised serious concerns about using allografts in this patient population. In one study, the risk of failure with bone-patella tendon-bone allograft was 2.6 times to 4.2 times higher than bone-patella tendon-bone autograft.”
Allograft processing
Another factor to consider, said Dr. Miller, is that modern allograft processing techniques have improved allograft safety.
“Not everyone who signs the back of a driver’s license is an acceptable donor, so it is good that nucleic acid testing for HIV-1 has reduced the time required to receive test results from 22 to 12 days,” he said.
Aseptic tissue recovery—meaning tissue recovery that does not involve contact with microorganisms—is important; however, sterility, or freedom from living microorganisms, cannot usually be achieved, said Dr. Miller.
“Sterile acquisition is just not possible in most settings, but the goal is to ensure that no further bioburden is introduced,” he said, noting that disinfection is required to lower the sterility assurance level (SAL), with a goal of reaching 10¯6 SAL.
Tissue processing, asserted Dr. Miller, is a “delicate balance between preserving the biologic function of the tissue and removing potentially infectious agents.”
Processing may include chemical disinfectants or terminal sterilization (irradiation).
“Processing methods must be validated to reduce the risk of terminal contamination and cross-contamination,” said Dr. Miller.
Secondary sterilization is used to address potential pathogens that may have survived the harvest and initial processing.
“All sterilization processes have the potential to affect the biomechanic and biologic properties, which is a major concern,” he said. “These techniques vary with every tissue bank.”
Dr. Miller explained that although low-dose irradiation is sufficient for bacteria and spores, higher doses are required to kill viruses, such as HIV.
“The more irradiation, however, the greater the potential for problems, because the biomechanic properties of the graft are adversely affected,” he said, noting that doses higher than 2.5 megarads (Mrads)—and, possibly even doses lower than that—can adversely affect mechanical properties.
Recent clinical studies have compared irradiated and nonirradiated grafts. “One study found a failure rate of 2.4 percent in nonirradiated Achilles allograft compared to a failure rate of 33 percent in Achilles allograft irradiated with 2.5 Mrads,” he said.
Dr. Miller recommends using only tissue banks that are accredited by the American Association of Tissue Banks (AATB), registered with the U.S. Food and Drug Administration and the state, and certified by the International Organization for Standardization.
“Do your research,” he said. “Make sure the tissue bank has a good safety track record and good clinical results. Understand the processing and packaging procedures they use. Ensure that the sterility level reached is 10¯6 SAL. Also, be aware of processing fees and the level of customer service provided.
“Although allograft safety has improved significantly over the last 15 years, some allograft tissue may not be sterile,” emphasized Dr. Miller. “Remember that not all tissue banks use the same methods for donor screening or for tissue harvesting, tissue processing, safety purification, and secondary sterilization. Implantation has risks: It can cause infection with significant morbidity and mortality.
“Ultimately, graft choice is up to the patient,” he concluded. The orthopaedist’s job is to help educate the patient.”
Disclosure: Dr. Miller—Saunders/Mosby-Elsevier, Wolters Kluwer Health/Lippincott Williams & Wilkins, and The Journal of Bone and Joint Surgery.
Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org
AAOS information statement on the use of musculoskeletal allograft tissue
Bottom Line

Although patella tendon autograft has long been considered the gold standard for ACL reconstruction, quadrupled hamstring autograft is another option. In addition, allograft safety has improved significantly in the last 15 years, making allograft a viable option in some patients.
Tissue banks may use different processes for the following: donor screening, tissue harvesting and processing, safety purification, and secondary sterilization.
Studies have found a high failure rate in young, active patients who undergo ACL reconstruction using allograft.

References

Barrett GR, Luber K, Replogle WH et al: Allograft anterior cruciate ligament reconstruction in the young, active patient: Tegner activity level and failure rate. Arthroscopy 2010 26(12):1593-1601. Epub 2010 Oct 16.
Rappé M, Horodyski M, Meister K, et al: Nonirradiated versus irradiated Achilles allograft: in vivo failure comparison. Am J Sports Med 2007 Oct; 35(10):1653-8. Epub 2007 May 21.

AAOS Now
April 2012 Issue
http://www.aaos.org/news/aaosnow/apr12/cover1.asp