Knee menisci

Last revised by Sonam Vadera on 10 Apr 2024

The knee menisci are fibrocartilaginous structures that sit within the knee joint, deepening the tibiofemoral articulation. Their main role is shock absorption, improve stability of the knee joint, and load transmission. They also play an important role in synovial fluid dynamic circulation and also considered by some to be involved in proprioception. 

There are two fibrocartilaginous menisci in the knee joint: a medial meniscus within the medial tibiofemoral compartment and a lateral meniscus within the lateral tibiofemoral compartment. Each meniscus is C-shaped in the transverse plane and consists of the following parts (from anterior to posterior):

  • anterior root attachment

  • anterior horn

  • body (located centrally)

  • posterior horn

  • posterior root attachment

In cross-section, they have a triangular shape, being thicker peripherally and thinning to a free-edge centrally. 

The medial and lateral menisci differ in size and shape as follows:

  • medial meniscus

    • C-shape - open and wide, almost semi-circular

    • larger than lateral meniscus

    • posterior horn substantially larger than anterior horn

  • lateral meniscus

    • C-shape - tight and closed off more like an incomplete circle, i.e. anterior and posterior tibial roots are very close to each other

    • smaller than medial meniscus

    • anterior and posterior horns same size

The meniscal surfaces are named according to a simple nomenclature which is particularly helpful when describing meniscal tears. 

  • superior articular surface - also known as femoral surface

  • inferior articular surface - also known as tibial surface

  • inner free edge

  • periphery 

The menisci are vascularized only via the periphery and the root attachments and therefore the inner portions are avascular. This has important implications on the healing and surgical management of meniscal tears.  

  • red zone: outer one-third

    • supply from the peripheral meniscal plexus, in turn formed from the medial, lateral and middle genicular arteries 6,8

  • white zone: inner two-thirds

    • no vascular supply; diffusion dependent 6

  • red-white zone: transition between outer third and inner two-thirds

    • reflecting the reality that the loss of perfusion is gradual and also variable from site to site, patient to patient

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