The ACL or anterior cruciate ligament is the most important ligament in the knee. When it is completely torn, it can lead to instability or buckling of the knee. Why is it so important? What makes it unique? Why doesn’t it heal? Why do surgeons recommend getting it fixed? Is it necessary to get it fixed if I CrossFit®? Are there things I should avoid in CrossFit and life if I don’t get it fixed? All good questions but let’s check out its anatomy first.

The ACL starts at the femur and inserts onto the tibia. It crosses from the outside to the inner side of the knee in a diagonal fashion. This is why it is called a cruciate ligament because it crosses the knee. It forms an X with the posterior cruciate ligament inside the knee. The other two major ligaments in the knee are medial and lateral collateral ligaments. They are on the inside and outside of the knee respectively. They also are extra-articular or located outside the knee joint capsule. So if you had a balloon like the knee joint capsule, the cruciates are inside the balloon and the collaterals would be stuck to the outer surface of the balloon.

The ACL has a blood supply and nerve endings that run through it. It is made of two bundles that tighten and relax depending on the angle of your bent knee. It also helps to prevent your knee from giving way when the knee rotates. The diagonal orientation of the ligament contributes to this stability. Seeing the complexity of the ligament also helps us understand why it is so unique.

The ACL can tear if the foot is planted, but the knee shifts forward too strongly. This can occur during a zig zag sprint, when a football player plants, or if a basketball player cuts. Typically a pop is felt 75% of the time and there is immediate pain and swelling. People often wonder why it swells so quickly. The swelling comes from the small artery that pumps blood into the joint. An orthopedic surgeon can examine the knee and tell if there is an ACL tear with a test called a Lachman test. If the knee has become very swollen and it is difficult to examine because of the swelling, then an MRI can confirm a tear also.

So imagine the two ends of the ACL sitting in the knee-remember what I said about them being inside the knee joint or a balloon. Because the blood keeps the ends apart from each other, the ligaments do not grow back together. This is in contrast to the collateral ligaments like the MCL which often heals by itself without surgery.

Fixing the ACL is called reconstructing it. Way back surgeons tried to sew it back together and it failed. They have tried to replace it with many different materials like Gore-Tex and polyester, but those did not work either. So we are reconstructing it with people’s ligaments and tendons or someone else’s who has donated them to science.

The reason surgeons recommend getting it fixed is because of the thing called buckling of the knee. This is more likely to occur with twisting and pivoting sports. Most people who have torn their ACL will never forget that feeling. It occurs when the knee collapses and does not support the weight of the athlete. What then happens is that the meniscus or shock absorbers in the knee can tear and the joint surfaces can also get injured when they hit against each other. We know that injury to the joint surfaces as well as meniscal loss can lead to arthritis. So fixing the ACL is to help someone continue to play sports and prevent arthritis.

For the CrossFit athlete, I have seen people with ACL tears have trouble with box jumps because of the landing. Also coming down from the rings or bar has to be done with care to prevent buckling. Running straight ahead is typically fine, as is biking or rowing. The one area of concern is with some of the Olympic lifts. If someone has heavy weight and lands in a jerk, without an ACL they have to be very careful to land appropriately. If the knees cave in and twist, they could potentially give out. Similarly in an overhead squat if the knees rotate in that could mimic a pivot and the knee could twist. So bottom line, lifting without an ACL is certainly OK but one would have to be cautious with higher weights that would place higher torque on the knee. Rehab and a brace can be tried but people tell me the knee brace can get in the way with deadlifting and cleaning. So, for a CrossFit athlete with no ACL or a new ACL tear, I usually recommend reconstruction. I believe it is better to give in, than to give way.