Written by Jonah Blatt, Registered Phsyiotherapist, MScPT, BScHK

I’ve been a pretty big sports fan for a while now (particularly the NFL), which means that well before I was a Physiotherapist I heard about professional athletes getting that big scary knee injury and tearing their ACL. This always meant that they were out for the rest of the season, and if they were on a team that I liked usually meant I was going to have a minor meltdown of sorts.

What exactly is the ACL though? PCL? MCL? Um, there’s an LCL too? These are the 4 ligaments of the knee, and their job is to stabilize the knee joint.

Ligaments connect bones to other bones, so they stabilize the knee by holding the femur (thigh bone) and tibia/fibula (shin bones) together. If the ligament is torn, damaged, or stretched, it can cause increased joint laxity or looseness. This makes the 4 ligaments of your knee important for the function of the knee, as well as pain.

The 4 Main Ligaments of the Knee

Let’s highlight the 4 ligaments of the knee and what they do to keep us moving well.

ACL stands for Anterior Cruciate Ligament. It sits inside the knee and keeps your tibia (shin bone) from moving forwards in comparison to your femur (thigh bone).

PCL stands for Posterior Cruciate Ligament. It sits inside the knee as well, but behind the ACL. It keeps your tibia from moving backwards in comparison to your femur (thigh bone).

MCL stands for Medial Collateral Ligament. It connects your tibia and femur across the inside of your knee, which keeps the knee from collapsing towards the opposite leg.

LCL stands for Lateral Collateral Ligament. The LCL is the opposite of the MCL. It runs across the outside of the knee, and prevents the knee from buckling towards that side.

What do these ligaments do?

All of these ligaments are important for the knee to be at it’s best. Ligaments are important to the knee because they provide support and stability to the joint, which allows us to move safely and with confidence.

These 4 ligaments are in place to protect the knee. They hold the joint together and in it’s proper alignment by stabilizing the two bones that make up the joint.

If we don’t have these ligaments holding our knee together, movement can become much more challenging and uncomfortable. An activity that may have been simple and pain free before will be met with apprehension and discomfort.

What if I hurt one?

The first thing we want to know when a ligament is damaged is which ligament was affected. There are 4 ligaments we discussed today, so understanding which to focus on is important. Manual testing, clinical reasoning, as well as diagnostic imaging are all extremely helpful here.

Ligaments become sprained, or torn, when damaged. The extent of the sprain or tear tells us a lot about how long we expect recovery to take. Mild sprains may take just a few weeks to recover, while significant sprains or tears may require much longer.

Working with a Physiotherapist and other members of your healthcare team is a great way to diagnose and manage knee ligament injuries. They can help you to understand if you injured a ligament, which one it is, and what to do about it!