ACL Surgery Heads Back to the Future

Interviewer: Lara C. Pullen, PhD; Interviewee: Anil S. Ranawat, MD


August 15, 2019

Editorial Collaboration

Medscape &

Anil S. Ranawat, MD

As one of the 10 most common injuries to the knee, a torn anterior cruciate ligament (ACL) is debilitating and has sidelined numerous professional athletes for up to a year. Fortunately, with the recent advances in sports medicine, a torn ACL is no longer the career-killer it used to be.

Medscape spoke with Anil S. Ranawat, MD, an orthopedic surgeon at the Hospital for Special Surgery in New York City, to learn more about the past, present, and future of ACL repair.

Could you provide a brief history of ACL repair?

Before there was arthroscopy, surgeons performed an arthrotomy; they opened up the knee in order to repair the ACL. This was a time-consuming and laborious operation, and the overall success wasn't that good.

ACL surgery gradually evolved to replacing the ACL instead of repairing it. So we moved from repair to reconstruction and tried various strategies (eg, synthetic grafts). In the United States, the patellar tendon (which connects the kneecap to the shinbone) became the gold standard. As we developed more arthroscopic techniques, we began to change the way we performed the procedure. In the past, we made two large incisions and placed a graft in the right place. But as we moved to less invasive arthroscopic surgery, we started putting the graft in the wrong place.

And that brings us to the present, where we've started saying, "Hey, remember how we used to do it with the bigger incisions, and placing the graft in a more anatomic position?"

What is that better position? And what does that mean for the patient and their outcomes?

For the most part, it is about the accuracy of your tunnel position on the tibia, where we placed the tendon a little more anterior in the tibia and a little lower on the femoral wall. When we became less accurate, we started placing it a little posterior in the tibia and a little vertical on the femur. That was a consequence of using the more minimally invasive techniques, which dominated the market in the early 1990s into the early 2000s.

You and others have written on ACL surgical reconstruction and its effects on biomechanics.[1,2] How does the change in insertion spots affect how a patient's knee heels in response to surgery?

There are lots of ways you can affect the patient based on the graft positioning. Tunnel positioning is one thing, but it's also the type of graft used and how you fix the graft. They're all related, so you can't say that one thing is paramount. It is critical to understand that ACL replacement involves a compilation of factors:

  • The type of patient you have and the natural personality of their knee;

  • The type of graft you use;

  • Where you place the graft;

  • How you fix the graft and with what tensioning device.

Individualized surgery is the future of the ACL restoration. In the past, we performed the same procedure in the very same way on all patients without consideration of these factors. We do not all wear the same size suit or dress, yet that's what we were doing in the '90s with ACL surgery.

How do you see the future unfolding?

We delved into computer navigation and better assessment of how a knee pivots or accelerates at one point, and all of those are the frontier of this field. But I believe that the near future is more closely related to understanding certain risk factors for why knees fail or don't do well and prognostic factors for why knees succeed and do well.

In looking at global registry data and compiling all of the information, you can now start to say, "Based on data, here are the five key metrics of your knee that suggest the way you should have your ACL replaced."

What are some of the risk factors that are bubbling up right now that might be of interest?

Right now, four major risk factors indicate that traditional procedures are much more likely to fail. These include:

  • An excessive posterior tibial slope; this is certainly a risk factor for tearing your ACL and having your ACL fail, if you have it reconstructed;

  • Having a certain type of graft inserted in the knee is another risk factor for a higher failure rate;

  • A knee that's very ligamentally lax, or a patient who is loose-jointed;

  • A knee that has genu recurvatum, resulting in excessive knee hyperextension.

And what are the prognostic factors for success?

The factors for success are the opposite of all of those: a knee that has less posterior tibial slope, recurvatum, and loose jointing; and a knee that probably has a patellar tendon graft versus a hamstring graft.

For the surgeon who is faced with one of these riskier knees, what's the best path forward?

First, it involves understanding the risk factors. It's not enough to say that you have a risk factor; it's also about how severe the risk factor is. For example, you could have a slightly elevated cholesterol or you could have an extremely high cholesterol level, and the latter puts you at higher risk for cardiovascular disease.

It's about objective quantification of risk factors. It's one thing if your risk is a little high, but it's another if it's exceptionally high. If you are on the extreme end of the spectrum, then an adjuvant procedure at the time of your ACL may be warranted. An anterolateral ligament reconstruction or an iliotibial band tenodesis (otherwise known as a Lemaire procedure) could potentially help a knee that has high-grade rotational instability. And on the rare occasions that you have a patient with very excessive slope, you could perform an osteotomy at the time of surgery to correct it.

The bottom line is that an ACL procedure will probably be successful for 85%-90% of patients. As you get into more extreme cases (patients presenting with risk factors), that's when you have to look for these outliers. If you use the same procedures on these outliers, that's where you have your failures.

So it's important to consider where patients are on that risk curve by reviewing their history, conducting a proper physical examination, and thoroughly analyzing their imaging. Assessing whether a patient has a mild, moderate, or high risk for failure should be done before surgery, not after they re-tear their graft.

The only way you'll understand why a procedure goes well is to understand why things fail. But failures are not that common and that's why you need pooled data or registry data to provide you with detailed information. So, for example, out of 1000 ACL procedures, there was a 10% failure rate according to the data. Why did that 10% fail?

There are a lot of knees out there that have failed ACLs and the patients are still doing very well clinically. We need better objective assessment tools to define the word "failure." Is failure having an unstable knee even though the patient feels great? Does failure mean the patient required a second surgery?

In addition to defining "failure," is there anything else on the horizon for the future of ACL?

I think the future of ACL is going back in time:

  • Reverting to traditional concepts and procedures, which is going back to more anatomic tunnel positioning that we did in the past and making two incisions;

  • Deciding whether ACL repair surgery is appropriate and for which patients;

  • Understanding that the concept of individualized surgery is becoming very in vogue, using these lateral extra-articular procedures which historically were very common but are not so common in the present;

  • Understanding osteotomy and slopes. For example, take a dog that tears his ACL. Veterinarians tried to repair or reconstruct it, and it didn't work. A dog has very excessive tibial slope, so every vet performs an osteotomy on a dog's ACL. This is now becoming more and more in vogue in human orthopedics—understanding how slope is a major issue for ACL tear, the success rates, and other factors.

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