Knee: ACL surgery

ACL injuries are very common and quite often are treated surgically.


ACL stands for anterior cruciate ligament. The ACL is one of the two intraarticular ligaments of the knee, the other one being the posterior cruciate ligament (PCL).

Who needs ACL surgery?

This question does not have a straightforward answer.

Not every patient with ACL tear needs surgery.

As reasons cited to do surgery, participation in sports is often cited.

What is the purpose of ACL surgery?

After a tear, the ACL does not heal itself, and the deficiency is permanent.

This represents two related but separate problems:

  1. Gross instability. During sports that involve pivoting and fast turns while running, the knee may feel unstable. Patients who have had that sensation describe it as the earth slipping under one's feet, and so on. The instability is a direct result of the injury. An intact ACL prevents forward shifting of the tibia on the femur.
  2. Abnormal kinematics. Even when gross instability has been addressed, there remains an abnormality of motion of the knee, which seems to predispose patients for development of knee arthritis later in life.

Instability and abnormal kinematics are related, but best considered separately. ACL reconstruction surgery is very good at correcting the gross instability, but does not correct the more subtle motion abnormalities. ACL surgery has never been shown to prevent development of arthritis later in life. Odds are high that approximately 10 years after ACL injury, with or without surgery, your knee will have arthritis.

And so, the goal of ACL surgery it to correct gross instability that becomes manifest during certain sports activities. It is not realistic to expect complete normality of the knee after an ACL injury, with or without surgery.

How is ACL surgery done ?

The original ACL ligament is not repaired. Instead, a new ligament is put in place. This involves drilling tunnels in bone, placing a ligament graft in the tunnels, and fixing each side of the ligament to each tunnel.

The surgeon and the patient have some choices to make:

  1. Allograft or autograft?
    • if allograft, what kind of allograft? Choices include BTB, hamstring, Achilles allograft.
    • if autograft, what kind of autograft? Choices include BTB, hamstring, quadriceps.
  2. Interference or suspensory fixation? Supplementary fixation?
  3. Last, but not least, there is a choice of various methods and instruments for drilling those tunnels. This is not trivial, as surgeons disagree on which method more accurately establishes the correct ACL footprint, and so on.

In professional orthopedic meetings it is common to see vocal disagreements between surgeons on every one of the above issues.

What is the double-bundle technique?

In an attempt to improve the kinematics and delay arthritis, the "double-bundle" reconstruction technique has been advocated by the good doctors at the University of Pittsburgh. While cadaver studies have shown better kinematics with double-bundle ACL reconstruction, prevention of arthritis in real patients is still not a realistic goal. For instance, studies from Finland and Japan (Suomalainen, Fujita) have shown no difference in real patients at two years after surgery. At this point, as far as surgery goes, traditional "single bundle" reconstruction remains as the standard technique.

Whether you should proceed with any reconstruction at all, remains as the more important question. My opinion is that the one good reason to proceed with ACL reconstruction surgery is the need for stability during sports that require cutting and pivoting. If you are not active in sports, or if the knee feels good enough to you, perhaps you should avoid surgery.

What is the typical recovery?

  1. Time for healing and incorporation of the graft is 1 year. While preliminary healing occurs in 6 weeks, the graft is still "dead" until it has been invaded and repopulated with blood vessels and live cells. Due to this process of recolonization and remodelling, the graft is actually weakest at about 6-7 months after surgery.
  2. Physical therapy and muscle rehabilitation after surgery is crucial. Without proper after-care one can develop stiffness, muscle atrophy from pain and immobility, etc.
  3. It is important to have realistic expectations. Among professional NFL players for instance, less than half are able to return to the game 1 year later, and that is with "the best" treatment and therapy that money can buy.

Case study

Below you will see a few arthroscopy pictures from my surgery on a 20 year old soccer player. He decided to have the surgery because he found that without surgery his knee felt unstable and he could not play at all.

The technique was anteromedial drilling with hamstring autograft, biocomposite transpin fixation on the femur, interference screw with supplemental 4.0 screw fixation on the tibia.

In this first picture, you see what's left of his old ACL. To the right of the picture is the medial wall of the lateral femoral condyle. A normal ACL blocks the view of that same wall. Instead here you see attenuated chronically ruptured remnants pf the ACL.

In this second picture you see the prepared femoral tunnel. This is where the ACL ought to be attached. The site has been cleaned, drilled, and you see a suture loop coming down from the depth; deep into the tunnel you see a transverse metallic wire that will be pulled down and out from the tunnel by the green suture. The suture will pull the wire loop completely out of the knee; The ACL graft will then be placed around the loop, and the wire loop will be used to pull the graft back into that tunnel. A sturdy transfix pin will then take the place of the wire, will go through the graft to hold it in place securely on the femoral side.

Here's the ACL graft in the femoral tunnel. (Compare with the previous picture.)

And here's the finished operation. The new hamstring graft takes the center of the picture.

Graft choice for the reconstruction is important. The main decision one has to make is between an autograft, and an allograft.

An autograft is harvested from the patient's own body. An allograft, on the other side, is tissue harvested from a donor, usually a dead donor. The obvious advantage of using allograft is that no tissues are harvested from the patient. One of the disadvantages is a higher failure rate. The MOON study has shown a higher failure rate (20% vs 6%) when comparing allograft with autograft in young patients. The other disadvantage of allografts is the risk of infection. Click on the appropriate link at the bottom of this page for further info on allografts.

My own preference is to use hamstring autograft. The only downside is loss of about 10% of knee bending strength in deep flexion, which is not a problem. Plenty of European soccer players have had their ACL reconstructed with hamstring autograft.

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