Dr. Joel Spring
- Nov 23, 2020
- 3 min read

What Does the ACL Do?

The ACL is one of 4 main ligaments of the knee. It is in the news a lot when athletes hurt or tear the ACL, but they never say what the ACL does.

Ligaments of the Knee

The four major ligaments of the knee are the Anterior Cruciate Ligament (ACL), the Posterior Cruciate Ligament (PCL), the Medial Collateral Ligament (MCL), and the Lateral Collateral Ligament (LCL). The two most common injured ligaments are the MCL and ACL.

Each of these ligaments adds support to the knee and helps to restrict certain motions at the knee. When too much of that motion happens, the ligament gets sprained similarly to spraining and ankle.

In the next section we will talk more about the ACL, but here is a brief description of what the other 3 ligaments do for the knee.

MCL- provides stability to the knee and prevents excessive knee buckling inward at the knee joint (towards the other leg)
LCL- provides stability to the knee and prevents excessive movement of the knee outward at the knee joint (away from the body)
PCL - proveds stability to the knee and prvents posteior movement of the lower leg at the knee joint.

The ACL

The Anterior Cruciate Ligament provides stability to the knee. It prevents the lower leg (tibia) from moving forward from the knee joint. When strain is put in this direction, the ACL can sprain mildly, moderately, or severely (this would be the ACL tear).

The ACL is important in activities that involve quick changes in direction (ex. tennis, soccer, basketball, etc.). It is not involved in activities that are primarily straight forward or backward (ex. walking, running, etc.).

Surgery is only required if you tear the ACL, and even then you still have a choice. Because of what the ACL does, it really depends on your long term health and fitness goals if you are going to have surgery or not. If you do not plan on playing sports or doing things that have a lot of cutting/direction changes, you may opt to not have surgery and just strengthen the hamstrings and quadriceps muscles (the back and front of the thigh respectively).

If you plan on returning to things like softball, tennis, or basketball then you have a harder decision to make when choosing to have surgery or not. Some people get a fitted brace that adds external support to the knee for when they do those high level activities. This may work fine for you.

As always, when deciding to have surgery, you need to weight the risks and benefits before you come up with a decision. If I ever tear my ACL I would consider what my long term life goals are before I decide on having surgery.

Rehabilitation For Any ACL Injury

If you have an ACL injury, whether it is torn or not, you will require strength around the knee to help you get back to full use and stability of your knee and leg. For any ACL injury the key components of rehab are strengthening the quadriceps and hamstrings. This also holds true for ACL injury prevention. Having strong, stable legs is the best way to avoid injury and to return to all of your favorite activities.

Here are some great exercises for you to do:

Deadlifts: