Knee Meniscus

The knee meniscus is a special layer of extra cartilage that lines the knee joint. Its job is to cushion the joint and transfer forces between the tibia and femur bones.

In most of our joints, including the knee, there is a layer of articular cartilage, which is made of collagen and chondroitin.  It provides a smooth surface over the bones. 

As a result of the large forces that go through the knee joint, an extra layer of cartilage is necessary - the meniscus. 

Here we will look at the role of this special knee cartilage, how it gets injured and what we can do to keep it healthy.

The knee menisci are two portions of thick, rubbery tissue that line the joint on the tibia. They have a fibrocartilaginous structure.  They sit on the top surface of the tibia (shin bone) in two crescent shaped parts.

1) Medial Meniscus: this is found on the inner side of the knee and is the larger of the two

2) Lateral Meniscus: this is found on the outer side of the knee

A majority of the meniscus has a poor blood supply with only the outer portion being vascularised.  As a result, a tear in the menisci is very slow to heal, if it can heal at all, unless it is in the outer portion that is served by blood vessels.

The knee meniscus is really important as it:

1) Helps the tibia and femur to fit better to each other (increases surface area contact by 40-60%), making the joint more stable
2) Provides a smooth surface between the femur and tibia, preventing bone rubbing on bone
3) Helps ensure correct weight distribution between the tibia and femur
4) Act as shock absorbers/cushions reducing the force going through the knee bones by about 30%
5) Contains nerves which help improve balance and stability

There are two ways that the knee meniscus gets damaged:

1) Injury: The menisci are often injured when the knee twists suddenly e.g. when playing sports or during a fall. This tends to tear part of the cartilage and can cause bleeding in the joint resulting in swelling

2) Wear and Tear: As we age, our cartilage becomes more brittle and can start to wear away. This also makes them more prone to injury. This is a common feature of arthritis

Meniscal tears can occur in any part of the cartilage (as shown in the diagram) and can take a long time to recover from.  Small blood vessels feed the outer edges of the meniscus but the middle parts have no direct supply which means it is very slow to heal following injury.

One of the most common signs of a meniscal tear is locking - where the knee gets stuck.  This happens which a flap of torn knee meniscus gets stuck in the joint block movement.  By wiggling your leg around, you can usually move the torn flap of meniscus out of the way, but the problem will keep occurring.  If this is the case, arthroscopic surgery will be advised to trim the flap. 

To find out more about knee cartilage injuries including the causes, symptoms and treatment options, visit the meniscal tear section.

We are all born with different quality knee cartilage which we can’t change, but we can help keep it healthy by ensuring that the muscles around the knee are strong so that less force goes through the knee meniscus. The best way to do this is by doing knee strengthening exercises.

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