The Knee Joint Complex, Utilitarian, and Essential!

Oct 28, 2013

Editor's Note: When you see these three dots surrounded by a gray rectangle — ¹ — you can click on it to get further information about the topic. Click a second time, and the message goes away.

This article was edited and updated on March 19, 2018.

The Importance of the Knee Joint

It may seem obvious how important the knee joint is: It allows us to bend and straighten our leg, and it supports our body while standing, walking, getting up from the floor, or climbing stairs. The knees work in conjunction with our feet and ankles to help us keep our balance.

Those who have ever injured their knees know how much we use them every day. Far too often, we take them for granted.

The Bones

The knee joint is like a hinge, and three bones are involved in its structure:

The Femur (thigh bone)
The Tibia (leg bone)
The Patella (the knee cap)

The femorotibial joint is where the femur and tibia come together.

The patellofemoral joint is where the patella and femur form a junction.

These two joints work together to allow the knee to bend and straighten. If you have a total knee replacement, it is these joints that are replaced.

Cartilage and Ligaments

We wouldn't like it much if those bones just rubbed against each other.

To prevent bone from rubbing on bone, the surfaces of all three bones are covered with a smooth gliding surface known as articular cartilage.

As well, there is cartilage that cushions the space between the two bone ends. The inner one is called the medial meniscus, while the outer one is called the lateral meniscus. Like the deltoid that shapes the shoulder, the meniscus cartilages form the shape of the knee. They also act as shock absorbers by distributing weight and reducing friction.

In addition to cartilage, there are four very important ligaments that surround, support and stabilize the knee. ² They are:

On one side of the joint is a cord-like structure known as the medial collateral ligament (MCL). It helps stabilize the knee.
On the other side of the joint is the lateral collateral ligament (LCL). It also helps stabilize the knee, but it is broader than MCL.
In the front center of the joint is the anterior cruciate ligament (ACL). It is an important stabilizer for the femur and prevents the tibia from rotating or sliding forward.
Directly behind the ACL is the posterior cruciate ligament (PCL). As you might have already guessed, the PCL prevents the tibia from sliding to the rear.

What can go wrong?

If damage is done to the smooth lining cartilage of the knee — and this usually happens as we age — then the surfaces of the bone begin to rub together. This causes pain, swelling, and stiffness. It's called osteoarthritis, and it's a common reason to have a knee replacement.

Some other causes of knee joint destruction are:

Rheumatoid arthritis: This causes inflammation of the tissue around the joint, which in turn causes deterioration of cartilage.
Post-traumatic arthritis: Arthritis may begin after an injury to the joint cartilage.
Avascular necrosis: This results from an inadequate supply of blood to the end of the bone inside the joint.
Misalignment of the knee joint: This occurs when, for whatever reason, the bones of the knee joint do not come together in the way that they should; whether or not the knee bows in or out, undue pressure is placed on the joint and, over many years, the joint will break down.
Tears of Ligaments or Cartilage: This injury happens often in sports activities, but it can also happen by just turning the knee awkwardly; repair and recovery can be anything from physiotherapy to surgery.

Some Common Injuries to the Knee

The knee is the largest and one of the most easily injured joints. It is formed by three bones: the lower end of the femur which rotates on the upper end of the tibia, and the knee cap (patella) which slides in a groove on the end of the femur.

Injuries often occur when changing or twisting direction rapidly, slowing down when running, and landing from a jump.

Knee injuries are common in contact sports, but they can happen in falls and accidents as well. Injuries to the MCL (medial collateral ligament) usually are caused by contact on the outside of the knee. A blow to the front of the knee or a misstep can cause injury to the PCL (posterior cruciate ligament). In athletic activities, meniscus tears usually occur when twisting, cutting, pivoting, or decelerating.

Two common injuries to the knee are:

Meniscus (Cartilage) and Ligament Tears: When the knee bends, the menisci (knee cartilage) compress to support the movement. When the knee bends and twists, the menisci may tear. The medial meniscus is especially vulnerable to tearing because it is anchored to the tibial collateral ligament (medial side of the knee) and so has less mobility than the lateral meniscus. A direct blow to the knee may tear the supporting ligaments. The direction of impact determines which ligaments are injured.
Ligament Injuries: These are the most common knee injuries. Of the four major ligaments found in the knee, the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) often are injured in sports. The posterior cruciate ligament (PCL) is also susceptible to injury.

The most important advice is to seek medical treatment as soon as possible and follow the prescription for treatment and rehabilitation.

Taking care of Your Knees

The trick to strengthening muscles around any joint is to find the appropriate exercise. Keep these rules in mind if you have injured your knee, or you just want to strengthen it, before embarking on any exercises:

Do slow movements of the knee first to warm up the synovial fluid.
Look for exercises that will increase muscle strength around the knee. Ask your physiotherapist for recommended exercises or look on the internet. Your fitness instructor might also have some ideas!
Don't over-do the repetitions. Sometimes an exercise can be appropriate, but the number of repetitions too strenuous. If you have pain, reduce the number of repetitions.
A good exercise to start with: Simply sit in a chair and stand up. Repeat as often as you wish, depending on your tolerance.
Check out The Hamstrings: Back of the Thigh and The Quadriceps: The Front of the Thigh for other exercises that will help strengthen the knee.