March 2016

Outcomes after ACL surgery: The importance of graft type

iStock_000016884945In an attempt to decrease the risk of re-rupture and revision surgery after anterior cruciate ligament reconstruction, practitioners are refining the decision process regarding which procedure is best for which patient.

By Cary Groner

Thomas Davis made headlines in February by playing in the Super Bowl with a broken left arm, but what’s most impressive about the Carolina Panthers linebacker is his right knee. Davis ended the January 17 playoff game against Seattle by fielding the Seahawks’ last-ditch onside kick with a spectacular leaping grab. It would have been a great play for anyone, but Davis made his jump on a right anterior cruciate ligament (ACL) that had been reconstructed three times.

Increasingly, people take such heroic athleticism in stride. But cases like that of Davis, in which patients reinjure the ligament and require revision surgery—sometimes more than once—have led experts to try to identify factors that may decrease the risk of subsequent rupture. The rigors of pro football notwithstanding, theories are all over the map. As more data become available, however, a guarded consensus is emerging.

Recent research has helped define the scope of the problem. Reported five-year revision rates after ACL reconstruction have been as high as 8.7%, and are significantly higher for patients younger than 21 years than for their older counterparts.1

Graft selection

In ACL reconstruction, surgeons use either autografts (tissue from the patient) or allografts (tissue from cadaver donors), and each approach has advantages and disadvantages. Allografts circumvent the problem of donor-site morbidity and offer robust tendons, such as the tibialis anterior, that couldn’t be harvested from a living donor. In one large US study, allografts were used in roughly 42% of primary and 79% of revision ACL reconstructions.2 Disadvantages include the risk of disease transmission, slower incorporation, and strength limitations, depending on how the tissue has been processed.3

Autografts include bone–patellar tendon–bone (BPTB) reconstruction, in which the graft is taken from the patient’s ipsilateral or contralateral knee. Although this approach is often considered the gold standard in the US, it is associated with a risk of anterior knee pain and other problems at the harvest site.3 As a result, many surgeons have turned to soft tissue grafts, particularly from the hamstring tendon; in recent years hamstring reconstruction has become the primary approach in Scandinavian countries.4 Recently, a few surgeons have begun using the quadriceps tendon, as well, and the percentage of such surgeries is expected to grow.5

But as surgery becomes more custom­ized, physicians continue to refine the decision process regarding which procedure is best for which patient. This affects choices about surgical procedure, graft harvest, and rehabilitation.

Not fail-safe

Two soccer players challenging for the ball, low angle view“We now know that the use of allografts in young people—particularly teenagers or very active people in their twenties and early thirties—is associated with a higher risk of graft tearing and revision,” said Steven Singleton, MD, an orthopedic surgeon with the Steadman Clinic in Vail, CO.

There are various reasons for this, he explained. With allografts, the body recognizes the tissue as non-native, and though it doesn’t reject the graft as it might a transplanted organ, it does mount an immune response that retards ligamentation and healing, leaving the graft weaker for a longer time than an autograft would be. The result, particularly in active young people, may be tissue stretching and breakdown leading to graft failure.

Jonathan Chang, MD, a clinical associate professor of orthopedics at the University of Southern California in Los Angeles, agreed.

“Graft selection is now influenced by age,” he said. “If you’re roughly twenty-five or younger, you’re usually better off with a patellar tendon autograft—though there’s discussion about where that tipping point is, and some put it at age forty or higher. As you get older, though, you probably have lower activity levels, so there are advantages to an allograft. The graft failure rates start equalizing at ages thirty-five to forty, so at that point, unless you’re a professional athlete, you’re likely to do well with any kind of graft.”

Recent research supports this perspective. For example, a Kaiser Permanente study of 21,304 ACL reconstruction patients found that those younger than 40 years had a higher risk of revision after allograft surgery than those with BPTB autografts; moreover, those younger than 21 years with hamstring autografts had a revision risk 1.6 times those who had BPTB autografts.1

“We found that the greatest differences occurred in the younger patients,” said Gregory Maletis, MD, the study’s first author, who is chief of orthopedics at Kaiser Permanente in Baldwin Bark, CA, and lead physician for the ACL registry there. “We also found that females are a little less likely to undergo revision, as are those with higher BMI [body mass index], who may be less active.”

Maletis told LER that he and his colleagues aren’t yet sure why hamstring autografts failed more often than BPTB autografts.

“It may have to do with graft diameter; smaller hamstring grafts may not withstand the loads as well,” he said. “We didn’t see that in the older patients, so it’s probably because the younger ones are doing higher-level sports and putting their knees at the greatest risk.”

Several recent studies have reached conclusions about graft type and longevity. For example, a 2014 study from Scandinavia found that patellar tendon autografts had a significantly lower risk of revision (hazard ratio .63) than hamstring autografts.4 A Norwegian paper from the same year reported a revision risk 2.3 times higher for hamstring grafts than patellar tendon grafts and four times higher for younger patients than older ones.6 A 2014 Danish study found that hamstring reconstructions were 1.4 times more likely to fail than BPTB ones (the authors also noted that use of hamstring tendons in Denmark increased from 68% in 2005 to 85% in 2011).7

A long-term randomized trial conducted in military personnel in Hawaii found that 10 years after reconstructive surgeries with either a hamstring autograft or a tibialis posterior allograft, more than 80% of grafts were intact and stable; however, allografts failed at three times the rate of autografts (26.5% vs 8.3%).3

Lead author Craig Bottoni, MD, chief of sports medicine in the Orthopedic Surgery Service at Tripler Army Medical Center in Honolulu, said surgeons minimized variables by using the same fixation and rehabilitation techniques in all patients.

“Allografts are an acceptable alternative for ACL reconstruction, but some do have a higher risk of failure,” Bottoni said.


Bottoni emphasized the importance of surgeons knowing as much as possible about the allograft tissue they use.

“It’s imperative to know what type of graft you’re using, where it comes from, and how it’s been processed,” he said. “Terminal radiation and some types of processing have been found to negatively alter the biomechanical properties of the allograft.”

Indeed, the Kaiser team concluded that certain factors seem to increase risk of allograft failure, including irradiation greater than 1.8 mrad, BioCleanse processing, younger patient age, male gender, and BPTB allograft.8

“Nonirradiated, nonprocessed grafts seem to hold up the best,” Maletis said. “There also appears to be a time-dependent relationship, in that we may not see failures within the first year or two. That may explain why studies with shorter time frames haven’t shown such differences with allografts.”

The finding that BPTB allografts had a higher risk of revision than soft tissue allografts (relative risk = 1.8) suggests processing may also weaken bone tissue, he added. A 2008 meta-analysis from the Mayo Clinic supports this finding.9


In a paper from the Steadman Clinic, researchers compared BPTB autografts to BPTB allografts and reported that, while functional outcomes were similar, 14% (n = 11) of allografts were revised by a mean of 4.7 years after surgery, whereas no autografts required revision. Moreover, patients aged 25 years or younger were 23 times more likely to require a revision than older patients.10

Like many surgeons, Singleton uses techniques he hopes will minimize his patients’ revision rates. He prefers BPTB autografts to hamstrings—though he’ll use the latter in patients with a history of patellar tendinitis or arthritis—and said that in his practice he sees very little anterior knee pain after BPTB surgeries.

“We’ve developed a small-incision technique to harvest the graft,” he said. “We also mobilize the patella right away in our rehab program, and I think those things minimize the potential for scarring.”

Jonathan Chang has his own take on the situation.

“I take twenty to thirty minutes harvesting the graft, carefully bone-grafting the harvest sites and doing a layered closure over the tendon without over straining it,” he said. “If you do that, you’ll have less postoperative bleeding and better function. If you don’t play close attention to how you treat that tissue, the patient has a higher risk of anterior knee pain.”

Donald Shelbourne, MD, who practices at the Shelbourne Knee Center at Community Westview Hospital in Indianapolis, favors a BPTB technique that many other surgeons shy away from: He harvests the graft from the contralateral knee rather than the injured one, and recently reported the approach was associated with better postoperative leg strength in both limbs and better strength symmetry while minimizing symptoms at the graft harvest site.11

“Back in the eighties, I found that we had trouble rehabbing the ACL-injured knee because we’d also taken a patellar tendon from it,” he said. “You can avoid that problem with cadaver or hamstring grafts, but I didn’t find those to be as successful—allografts failed, hamstring grafts left the patients weaker. When we started doing contralateral grafts in revision surgeries, we realized that it was a better approach because we had two independent rehabs instead of two rehabs in the same knee. We’ve now done over four thousand primary ACL reconstructions that way, and I think it’s the best answer. My goal is to give the patient two good knees, and I can do that more predictably when I take the graft from the opposite knee.”

Shelbourne, who keeps detailed data about his procedures and outcomes, said his team had collected information about their ACL repairs in 52 college soccer players. Of those who had ipsilateral BPTB reconstructions, 77% were playing at their previous level a year later, whereas 91% of those who’d had a contralateral graft returned to that level (unpublished data). One reason for the greater success, he said, is that contralateral harvesting leads to better healing at the donor site.

“The two thirds of the tendon we leave grows back to normal,” he said. “We didn’t see that when we took the graft from the same knee, because we had to rehab the ACL and couldn’t focus on the donor site. You need high-repetition, low-resistance exercises in the first month, and you can’t do that when you take the graft from the same knee that you’ve operated on for the ACL.”

Other surgeons told LER that while they use contralateral grafts for revision procedures, they remained reluctant to do so in primary reconstructions.

Anatomic accuracy of tunnel drilling can also affect outcomes, Singleton said.

“In the original arthroscopies in the late eighties and early nineties, surgeons used one approach to drill a tunnel in the femur and a second one to drill the tibia, and the graft was anchored in those tunnels,” he said. “Then, in the mid-nineties, an all-endoscopic technique was developed in which you drilled the tibial tunnel first, then used that to drill the femoral tunnel. That technique is still used by many doctors, with reasonable success; the problem is that it doesn’t allow one to get the [femoral] tunnel in the exact anatomic location of the native ACL. Steadman, Shelbourne, and a few others recognized this and continued to drill both tunnels independently. What I see clinically is that there is a lower rate of graft re-tears in ACLs done with independent tunnel drilling. You want the graft in the exact location it needs to be in.”


Surgeons and therapists stress the importance of proper rehabilitation, though there’s professional disagreement about what constitutes it.

“Rehab may be more crucial than the surgery itself,” said Craig Bottoni. “You want the patient to get back to activity as soon as possible without compromising the graft. Most of us are big advocates of extension, because if you don’t get it back in the early phase, it’s difficult to get it back later.”

Shelbourne emphasized both extension and delay in loading the ACL-injured leg.

“The first week after surgery, it’s too soon for things like riding a bike and walking,” he said. “Those can just leave the knee more inflamed and swollen. In terms of long-term rehab, though, we want to achieve full flexion, full strength, full function, and identical motion with the contralateral side.”

Shelbourne and his colleagues have documented the importance of achieving full extension, including terminal hyperextension symmetric to the opposite knee, and suggest concerns that this may overstress the graft are unsubstantiated.12

For Singleton, controlling swelling and regaining full range of motion drive the protocol in the first couple of weeks.

“We teach the patient to elevate the knee so the leg wants to come straight, and to some extent we’ll use a continuous passive motion machine to prevent adhesions and minimize swelling,” he said.

Rehabilitation should account for graft type, too, according to Jonathan Chang.

“When surgeons use allografts, they usually slow the rehab process a little to be sure that the incorporation has really taken hold before they start pushing the patient,” he said.

Bottoni added that, in general, clinicians are adjusting their expectations about return to sports.

“It used to be six months, but now people are saying that before nine or twelve months, patients don’t really have their proprioception back. Their quadriceps are still weak, so there is a risk for re-tear, especially in elite athletes,” he said.

Other researchers have reported the importance of quadriceps strength for achieving biomechanical symmetry during rehab, in fact.13,14

Clinicians at the University of Delaware in Newark are exploring a new rehab protocol involving a form of neuromuscular work they call postoperative return-to-sports training.15 The approach uses a series of progressive perturbations on unstable surfaces in both bilateral and unilateral stance, in conjunction with distractions and other tasks.

“People haven’t been using uniform or even very stringent rehab criteria,” said Lynn Snyder-Mackler, PT, ATC, alumni distinguished professor of physical therapy, and one of the study’s designers. “In this approach, we perturb the support surfaces; something unexpected happens, so how do you control your knee? In ten sessions over a couple of weeks, we increase the challenges and they get better at it. You’re trying to incorporate new movement patterns into sport-specific activities.”

In the clinical trial, all patients will receive quadriceps strengthening and agility drills, while only some will receive the perturbation training. Ideally, results will be published within the next year or two.

“It’s a hard thing to say to a kid, but if all they’re focused on is getting back on the field, that might be to their detriment,” Snyder-Mackler said. “They need to think about not having the second injury, and that might mean waiting a year.”

Cary Groner is a freelance writer in the San Francisco Bay Area.

  1. Maletis GB, Chen J, Inacio MC, Funahashi TT. Age-related risk factors for revision ACL reconstruction: a cohort study of 21,304 patients from the Kaiser Permanente anterior cruciate ligament registry. Am J Sports Med 2016;44(2):331-336.
  2. Maletis GB, Inacio MC, Funahashi TT. Analysis of 16,192 ACL reconstructions from a community-based registry. Am J Sports Med 2013;41(9):2090-2098.
  3. Bottoni CR, Smith EL, Shaha J, et al. Autograft vs allograft anterior cruciate ligament reconstruction: A prospective, randomized clinical study with a minimum 10-year follow up. Am J Sports Med 2015;43(10):2501-2509.
  4. Gifstad T, Sole A, Strand T, et al. Lower risk of revisions with patellar tendon autografts compared with hamstring autografts: a registry study based on 45,998 primary ACL reconstructions in Scandinavia. Am J Sports Med 2014;42(10):2319-2328.
  5. Lubowitz JH. Quadriceps tendon autograft use for ACL reconstruction predicted to increase. Arthroscopy 2016;32(1):76-77.
  6. Persson A, Fjeldsgaard K, Gjertsen JE, et al. Increased risk of revision with hamstring tendon grafts compared to patellar tendon grafts after anterior cruciate ligament reconstruction: a study of 12,643 patients from Norwegian cruciate ligament registry, 2004-2012. Am J Sports Med 2014;42(2):285-291.
  7. Rahr-Wagner L, Thillemann TM, Pedersen AB, Lind M. Comparison of hamstring tendon and patellar tendon grafts in anterior cruciate ligament reconstruction in a nationwide population-based cohort study: results from the Danish registry of knee ligament reconstruction. Am J Sports Med 2014;42(2):278-284.
  8. Tejwani SG, Chen J, Funahashi TT, et al. Revision risk after allograft anterior cruciate ligament reconstruction: association with graft processing techniques, patient characteristics, and grafts type. Am J Sports Med 2015;43(11):2696-2705.
  9. Krych A, Jackson J, Hoskin T, Dahm D. A meta-anlaysis of patellar tendon autograft versus patellar tendon allograft in anterior cruciate ligament reconstruction. J Arth Rel Surg 2008;24(3):292-298.
  10. Steadman JR, Matheny LM, Hurst JM, Briggs KK. Patient-centered outcomes and revision rate in patients undergoing ACL reconstruction using bone-patellar tendon-bone autograft compared with Boeing-patellar tendon-bone allograft: a matched case-control study. Arthrosc 2015;31(12):2320-2326.
  11. Shelbourne KD, Beck MB, Gray T. Anterior cruciate ligament reconstruction with contralateral autogenous patellar tendon graft: evaluation of donor site strength and subjective results. Am J Sports Med 2015;43(3):648-653.
  12. Benner RW, Shelbourne KD, Gray T. The degree of knee extension does not affect postoperative stability or subsequent graft tear rate after anterior cruciate ligament reconstruction with patellar tendon autograft. Presented at the 41st annual meeting of the American Orthopaedic Society for Sports Medicine, Orlando, FL, July 2015.
  13. Schmitt LC, Paterno MV, Ford KR, et al. Strength asymmetry and landing mechanics at return to sport after anterior cruciate ligament reconstruction. Med Sci Sports Exerc 2015;47(7):1426-1434.
  14. Palmieri-Smith RM, Lepley LK. Quadriceps strength asymmetry after anterior cruciate ligament reconstruction alters knee joint biomechanics and functional performance at time of return to activity. Am J Sports Med 2015;43(7):1662-1669.
  15. White K, Di Stasi SL, Smith AH, Snyder-Mackler L. Anterior cruciate ligament – specialized post-operative return to sports (ACL-SPORTS) training: a randomized controlled trial. BMC Musculoskel Disord 2013;14:108.

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