The meniscus is a crescentic wedge of fibre-filled cartilage, seated in the gap between the two long bones of the knee (tibia and femur). Each knee has two menisci - medial meniscus (inner aspect) and lateral meniscus (outer aspect).

knee joint showing the meniscus

The outer rim of a knee meniscus is wider and better supplied with fibres and blood vessels.

fingers explaining shape of lateral meniscus

The lateral (outer) meniscus is more 'O-shaped' than the medial meniscus, which is more 'C-shaped'. At the far ends are the two 'horns'.

knee meniscus showing the menisco-capsular junction

Areas of the outer rim, especially on the medial meniscus, are intimately related to the capsule.

 

What does the knee meniscus do?

The menisci are the shock absorbers of the knee. Their crescentic shape, with a wider outer rim and a flattened inner rim, allow them to absorb the vertical forces going through the joint, channelling the forces towards the outer edge where the fibre bundles are more tightly packed. Thus the outer edge absorbs more stress.

 

Components of the knee meniscus

meniscus relationshipsThe two menisci - medial and lateral - are shaped differently.

The lateral meniscus is 'O'-shaped and is quite mobile. The capsular attachments at the outer rim are not strong, and there is a defect in the capsular attachment where the popliteus tendon passes. So it can glide when the knee is twisted, and tears are less common.

The medial meniscus, in comparison, is 'C'-shaped with strong capsular attachments and is relatively immobile, unable to glide much when the knee is twisted, and thus suffering more tears.

 

What is a meniscus tear?

A meniscus tear is a disruption in the fibre structure of the meniscus, often following a twisting incident. Tears can be vertical or horizontal.

 

Can a meniscus tear heal on its own?

Healing of a meniscus tear depends on a number of factors:

  • How extensive the tear is. Larger tears are less likely to heal on their own.
  • Whether the tear is longitudinal, radial or horizontal. Longitudinal tears are more likely to heal than the other two.
  • The blood supply. Tears towards the inner rim have poorer blood supply and are less likely to heal.

 

Blood supply of the meniscus

blood supply of the meniscusThe blood supply of the meniscus comes from the outer capsule. This means that the outer rim of each meniscus is well supplied with blood, and tears in this area have a good opportunity to heal. On the other hand, the blood supply progressively reduces as it approaches the inner rim, so tears of the inner rim do not heal well.

When a surgeon describes the position of a tear he may refer to it being in the 'red' zone (implying the outer rim) or in the 'white' zone (implying the inner rim.

Synonyms: 
Knee cartilage
Knee cartilages
Semi-lunar cartilage
Semi-lunar cartilages
Meniscal cartilage
Meniscal cartilages
Menisci
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Webinar recording of event hosted in July 2020 about current options for patients who have lost their medial meniscus

Meniscus tears

Discusses how a meniscus can become injured, and the types of meniscus tear and their consequences

Meniscus Library

Library of excerpts from the medical literature about the Meniscus, with links to PubMed

A discussion of the differences between the two menisci in terms of their mobility, and what this means in terms of meniscus injury patterns.

Meniscus Avulsion

This eBook discusses the consequences of part of the knee meniscus or shock absorber tearing away from its moorings on the tibia bone.

Clearing up confusion about knee cartilage

This eBook discusses a common knee terminology muddle about the word 'cartilage'.

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