Medial meniscus

Medial meniscus
Head of right tibia seen from above, showing menisci and attachments of ligaments. (Medial meniscus visible at left.)
Left knee joint from behind, showing interior ligaments.
Latin	meniscus medialis
Gray's	subject #93 343

The medial meniscus is a fibrocartilage semicircular band that spans the knee joint medially, located between the medial condyle of the femur and the medial condyle of the tibia. It is also referred to as the internal semilunar fibrocartilage. It is a common site of injury, especially if the knee is twisted.

Structure

The meniscus attaches to the tibia via meniscotibial (coronary ligaments).

Its anterior end, thin and pointed, is attached to the anterior intercondyloid fossa of the tibia, in front of the anterior cruciate ligament;

Its posterior end is fixed to the posterior intercondyloid fossa of the tibia, between the attachments of the lateral meniscus and the posterior cruciate ligament.

It is fused with the tibial collateral ligament which makes it far less mobile than the lateral meniscus. The points of attachment are relatively widely separated and, because the meniscus is wider posteriorly than anteriorly, the anterior crus is considerably thinner than the posterior crus. The greatest displacement of the meniscus is caused by external rotation, while internal rotation relaxes it.

During rotational movements of the tibia (with the knee flexed 90 degrees), the medial meniscus remains relatively fixed while the lateral part of the lateral meniscus is displaced across the tibial condyle below.

Function

The medial meniscus separates the tibia and femur to decrease the contact area between the bones, and serves as a shock absorber reducing the peak contact force experienced. It also reduces friction between the two bones to allow smooth movement in the knee and distribute load during movement.

Injury

Acute injury to the medial meniscus fairly often accompanies an injury to the ACL (anterior cruciate ligament) or MCL (medial collateral ligament). A person occasionally injures the medial meniscus without harming the ligaments. Healing of the medial meniscus is generally slow. Damage to the outer third of the meniscus will often fully heal, but the inner two thirds of the medial meniscus has a limited blood supply and thus limited healing ability. Large tears to the meniscus may require surgical repair or removal. If the meniscus has to be removed (menisectomy) because of injury (either because it cannot heal or because the damage is too severe), the patient has an increased risk of developing osteoarthritis in the knee later in life.

More chronic injury occurs with osteoarthritis, made worse by obesity and high-impact activity. The medial meniscus and the medial compartment are more commonly affected than the lateral compartment.

See also

• meniscus
• tear of meniscus
• cartilage
• unhappy triad
• meniscal cartilage replacement therapy

Additional images

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  Right knee-joint, from the front, showing interior ligaments.

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  Sagittal section of right knee-joint.

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  Capsule of right knee-joint (distended). Posterior aspect.

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  Normal medial meniscus

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  Anterior view of knee.

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  Right knee in extension. Deep dissection. Posterior view.

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  Right knee in extension. Deep dissection. Posterior view.

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  Knee and tibiofibular joint.Deep dissection. Anterior view.

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  Knee joint. Deep dissection. Anterior view

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  Knee joint. Deep dissection. Posterior view

References

• Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1. 
• Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. 2006. ISBN 1-58890-419-9. 

External links

• SUNY Figs 17:07-06
• Medial+meniscus at eMedicine Dictionary
• lljoints at The Anatomy Lesson by Wesley Norman (Georgetown University) (antkneejointopenflexed)
• The KNEEguru
• Medial Meniscus Tear Knee MR

This article incorporates text from a public domain edition of Gray's Anatomy.