Medial meniscus

At a glance

English

Medial meniscus

Latin (TA2)

Meniscus medialis

System

Cartilage

Region

Lower limb

Side

Paired, left and right

About the medial meniscus

The medial meniscus is a C-shaped band of fibrocartilage resting on the inner tibial condyle, under the femur's inner condyle. It is the inner of the two menisci; the lateral one is closer to a full circle, whereas the medial one is an open crescent. In section it is a wedge, thick at its outer, attached edge and tapering to a thin free inner border. It is noticeably broader behind than in front, so its back part carries more of the load.

Its horns are widely separated. The thin, pointed anterior horn is attached on the front of the tibial intercondylar area, ahead of the anterior cruciate ligament, and is joined to the lateral meniscus by the transverse ligament of the knee. The thicker posterior horn is fixed on the back of the intercondylar area, with the lateral meniscus attached in front of it and the posterior cruciate ligament behind. Around its outer margin the meniscus is bound to the edge of the tibia by short coronary ligaments, and it is firmly united with the deep part of the tibial (medial) collateral ligament and the capsule.

These attachments make the medial meniscus much less free to move than its lateral partner. When the flexed knee rotates, the lateral meniscus slides over its condyle while the medial one stays nearly fixed; external rotation strains it most, and internal rotation slackens it. The meniscus keeps the femur and tibia from bearing on a small point of contact: it spreads load over a wider area, cushions peak forces, reduces friction and helps lubricate and steady the joint.

Because it cannot move out of the way, the medial meniscus is torn more often than the lateral one, particularly by twisting a bent, weight-bearing knee. Its injury often goes with tears of the anterior cruciate or medial collateral ligament. Only the outer third, the red zone, has a good blood supply and can heal after repair; the inner two-thirds, the white zone, is fed by synovial fluid and heals poorly, except sometimes in young children. Large tears may need arthroscopic repair or partial removal, and losing meniscal tissue raises the later risk of osteoarthritis, which already favours the medial compartment. In selected young patients a meniscal transplant is possible.

Attachments and function

Attaches from

Anterior horn on the front of the tibial intercondylar area, ahead of the anterior cruciate ligament.

Attaches to

Posterior horn on the back of the intercondylar area, behind the lateral meniscus and ahead of the posterior cruciate ligament; its outer margin is held to the tibia by coronary ligaments and united with the tibial collateral ligament.

Function

Deepens the medial tibial condyle, spreads load, absorbs shock, reduces friction and stabilises the medial compartment of the knee.

Nerve supply

Its outer part receives twigs from the genicular branches of the tibial and obturator nerves.

Blood supply

The outer third is supplied by the medial and middle genicular arteries through a perimeniscal plexus; the inner two-thirds relies on diffusion from synovial fluid.