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What ACL Graft Should I Choose?

“A wise man makes his own decisions. An ignorant man follows the public opinion.” – Grantland Rice

Last week, we discussed the first decision you will have to make after blowing out your knee. Surgery or no surgery? Perhaps you have decided to manage your rehabilitation conservatively. Excellent. Find a physical therapist you can trust and get after it!

If you have decided that surgery is the best option for you, here comes decision number two. Too often do we blindly accept the opinions of others – without considering our own thoughts and/or needs. This is especially true in healthcare when patients automatically follow the recommendations of their providers without considering all of the options. How can you possibly make an informed decision if you don’t have all of the facts? Disclaimer: I am probably the worst decision-maker of all time – but here are some facts to help you navigate your next big decision. Remember, it is important to realize that there is no one correct answer. What is best for you may be drastically different than what’s best for someone else depending on your age, goals, and lifestyle demands.

When reconstructing the ACL, you have a couple of options. There are a few less conventional ideas/methods out there, as well as some super cool experimental trials, but it usually comes down to these four:

  • allograft
  • hamstring tendon soft tissue-bone autograft
  • patellar tendon bone-tendon-bone autograft
  • quadriceps tendon autograft

As we know from previous posts, autografts are pieces of tissue from a different part of YOUR own body. Allografts, on the other hand, are comprised of tissues from cadavers. A quick Google search should clear up any confusion you might have regarding the definition of “cadaver.” Autografts and allografts are typically made up of tendon that remodels over time, forming an ACL-like substitute, or graft. The graft often results in a stable knee, but surgery can also increase your risk of developing osteoarthritis later in life. Unfortunately, this is also the risk you take when electing not to have surgery on your knee, as the odds of cartilage lesion increase by 1% for each month that elapses after injury without surgical intervention.

Allografts are usually made up of a strong tendon from a cadaver’s lower extremity. The achilles and patellar tendons are most frequently used, but some surgeons use the IT band, anterior or posterior tibialis is well. Surgeons often suggest allografts, as there is considerably less pain and no “donor site morbidity,” meaning you don’t have to “rob Peter to pay Paul.” With autograft procedures, surgeons must compromise a previously uninjured part of your knee to repair the ACL. This can make things like kneeling extremely troublesome in the future. Allograft procedures also require less operating room time, so you might spare your insurance company a couple extra bucks. While these are all nice pros to consider, don’t neglect to look at the cons. Anytime you introduce foreign tissue to your body, you risk the body launching an immune response degrading the tissue, or rejecting the graft. Meaning you might go through months of recovery, just to find out you get to do it all over again. Though very slight with today’s technological advances, you also risk disease transmission. All graft donor sources are tested for diseases like HIV and bacterial infections, but the risk of acquiring such a pathology is still there (though minuscule). Additionally, since allografts are devoid of living cells, they actually take longer to heal than autografts. This seems to be a common misconception in sports medicine, so I like to educate all of my patients before they go under the knife. I don’t usually like to tell people how to think, so I will let you come to your own conclusions and leave this small statistic right here. In a recent study looking at patients under the age of 18 with closed growth plates, there were no significant differences in function, activity, or satisfaction between allograft and autograft groups. However, the allograft group had a failure rate 15 times greater than that of the autograft group, with all failures occurring within the first year after reconstruction… I had an allograft reconstruction once. Ask me if it lasted.

The hamstring autograft is another option you might go with. Don’t worry – I’ve tried this one too. In this procedure, the surgeon makes a small incision over the top of your shin bone where the hamstring tendons attach (also known as per anserine, or “goose foot.”) The ends of your hamstrings are detached from the shin bone and harvested to make a graft. The semitendinosus and gracilis are long skinny tendons and lend themselves well to be made into either single-bundle or double-bundle grafts. Your native ACL has two distinct bundles; one (anteromedial) prevents translatory instability, while the other (posterolateral) prevents rotatory instability. While different surgeons advocate for different techniques, there is a collection of research stating that there is no significant difference in functional measures or clinical evaluation between single and double-bundle techniques. Hamstring tendon grafts also keep your knee extensor mechanism (your quadriceps) intact and are often considered less painful. This can mean less quad inhibition and quicker return of quad strength post surgery.

A native, uninjured ACL can withstand 2160 Newtons of force. A semitendinosus gracilis graft, on the other hand, can withstand 4140 Newtons of force. The tendons are readily available and actually grow back to the attachment site via the “lizard phenomenon” – something I had no idea actually existed until a recent conversation with Dr. Brian McKeon over at Boston Out-patient Surgical Suites in Waltham. I, like many, had previously thought that the detached hamstring tendons simply retracted up into the thigh and that this was the reason why many patients possess knee flexion strength deficits post hamstring ACL-R. Research has shown that a torque deficit in deep knee flexion is almost always present postoperatively in these patients, but that the cause for this remains unclear.

That brings me to the first (and perhaps most influential) con. Based on where the hamstrings sit anatomically, they help prevent anterior translation of the tibia in open kinetic chain. Meaning, they assist the ACL and play a fundamental role in knee stability. So why would you want to significantly decrease the strength of something that actually protects the ACL? This is especially true when we are talking about quadriceps-dominant female soccer players. Recall from a previous post, that as relative quadriceps strength increases and hamstring strength decreases, the risk of ACL tear goes up. Perhaps this is why ACL reconstructions with hamstring autografts have a higher re-injury rate than some alternatives. But if you have a hamstring autograft – don’t panic! Find a qualified strength and conditioning professional and/or medical practitioner and bulk up your posterior chain. Hamstring and calf eccentrics all day! Other cons to the hamstring autograft include possible shortening of the tissue surrounding the posterior capsule of your knee, making terminal knee extension (straightening your leg fully) a little bit harder to achieve post-operatively. Unlike the patellar tendon autograft, which involves bony integration, the hamstring graft requires soft tissue-to-bone healing. This typically takes a little bit longer and requires a slower rehabilitation to ensure protection of the graft. Don’t worry – we will go through specifics of the rehabilitation process in a later blog.

The patellar tendon bone-tendon-bone autograft is currently considered the gold-standard for ACL reconstruction. The graft is taken from your patellar tendon (aka patellar ligament) – the structure attaching your kneecap to your shin bone. The surgeon will cut out the middle third of the tendon, along with a small piece of bone from your knee cap and from your shin bone. He/she will then drill tunnels into your shin and thigh bones and pull the graft through, connecting the two tunnels and plugging the ends with bone. This tissue will essentially serve as a latticework for your new ACL to grow. The patellar tendon can withstand up to 2977 Newtons of force and is approximately 174% stronger than your native ACL at the time of harvest! The ACL-like structure initially weakens, reaching its weakest and most vulnerable point in rehab at around 8-12 weeks post-op, but then re-vascularizes and increases in strength. The patellar tendon bone-tendon-bone graft is easily accessible, possesses excellent strength, and has excellent long-term results reported in the literature. In fact, numerous studies have shown that the re-tear rate for patellar tendon autografts is significantly less than that of allograft or hamstring autograft. The patellar tendon also allows aggressive rehab, as bone-to-bone healing is much faster than soft tissue-to-bone. Clinicians should be cognizant of loading the knee past 60 degrees of closed-chain flexion for the first 6-8 weeks, however, to avoid patellar tendon irritation. Along with its pros, the patellar tendon also has numerous cons. For starters, the patellar tendon is flat and does not easily allow the double-bundle technique mentioned above. There is also risk of patellar fracture, tendon rupture, tendinitis, and excessive scar tissue that can lead to arthrofibrosis and/or other range-of-motion complications. Perhaps most noticeable is the donor site morbidity we talked about earlier. Diffuse anterior knee pain is a common development with patellar tendon autografts and may present a challenge for patients who must kneel or crawl for their occupation. Since this graft is taken from the tibial tuberosity, it is not an option for children/adolescents with open growth plates, as it can lead to donor-site growth disorder.

Your last option is the quadriceps tendon autograft. While less popular, many studies have actually shown that the quad tendon graft is just as successful as the hamstring or patellar tendon autografts. Single-bundle ACL reconstructions with quad tendon autografts have shown equal muscle recovery and knee stability when compared to hamstring tendon grafts. Quad tendon grafts also result in less kneeling pain, graft site pain, and sensation loss, with similar anterior knee stability and subjective outcome measures when compared to patellar tendon autograft. The quad tendon autograft has nearly twice the size of the patellar tendon cross-sectional area and can withstand up to 2353 Newtons of force. It is also a readily available, but is perhaps more technically demanding on the skillset of the surgeon. Other cons include the fact that a scar on the anterior thigh may be cosmetically unappealing, and that due to lack of popularity, there is still limited research on long-term outcomes. Quad tendon autografts are completely viable and a good alternative to the patellar or hamstring graft.

So there it is. You have all of the facts in front of you and must now make the best possible decision for YOU. Are you an athlete? Does your sport require multidirectional stability? Is this your first ACL tear or do you need a revision? Are you a quad-dominant female athlete? Are you just looking to get back to pain-free ambulation with normal functional mobility? Don’t sell yourself short. Be sure to discuss all of your options with your surgeon and play an active roll in your healthcare. Ask questions! Afterall, you’re the one who will be stuck with the outcome forever. Stay posted for upcoming blogs on the benefits of prehabilitation, what to expect after surgery, and how to cope with the psychological side of injury. Don’t forget to share this with a friend in need. Until next time, be well.


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