Knee Meniscus
By Chloe Wilson, BSc(Hons) Physiotherapy
The knee meniscus is a special layer of extra cartilage that lines the knee joint.
The job of the meniscus is to cushion the knee joint and transfer forces between the tibia and femur, the thigh and shin bones.
Most of the joints in our body are lined with a thin layer of articular cartilage, made of collagen and chondroitin. This provides a smooth surface over the bones allowing smooth movement.
The knee joint also has an additional layer of special cartilage, called the meniscus. The reason that the knee needs this extra thick layer is to protect it from the huge forces that go through the joint as we move.
Here we will look at the role of this special knee cartilage, how it gets injured and what we can do to keep the meniscus healthy.
The Structure of the Meniscus
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: is found on the inner side of the knee and is the larger of the two
2) Lateral Meniscus: is found on the outer side of the knee
The meniscus has two distinct areas, the White Zone, which does not have a blood supply, and the Red Zone, which does have a blood supply being vascularised by the joint capsule.
As the inner portion of the knee meniscus doesn't have a blood supply, tears to the White Zone do not usually heal naturally, often requiring surgery.
Tears to the outer zone can heal as the Red Zone receives nutrients, oxygen and chemical via the blood from the joint capsule, however it tends to be a slow process.
Knee Meniscus Function
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
How Does It Get Injured?
There are two ways that the knee meniscus can be 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.
How Can I Look After My Knees?
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.
Page Last Updated: 11/10/18
Next Review Due: 11/10/20
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