Knee menisci

The knee menisci are fibrocartilaginous structures that sit within the knee joint, deepening the tibiofemoral articulation. They function to improve stability, shock absorption and load transmission of the knee.

Gross anatomy

There are two knee menisci in each joint- medialand lateral. They are semilunar or curved in shape. The menisci are described as having a central body with anterior and posterior horns. In cross-section, they have a triangular (bow-tie) shape, being thicker peripherally and thinning to a free-edge centrally. Each meniscus has a differing shape, size and attachments:

• medial meniscus:
  • larger
  • more open and wider; semi-circular in shape
• lateral meniscus:
  • smaller
  • narrower and more C-shaped

Attachments

• medial meniscus:
  • the anterior horn of the medial meniscus attaches immediately anterior to the tibial attachment of the anterior cruciate ligament (ACL) in the intercondylar area
  • lateral aspect attached to the deep (third) layer of the medial collateral ligament
• lateral meniscus:
  • the anterior horn of the lateral meniscus attaches immediately posterior to the tibial attachment of the ACL on the intercondylar area
  • no attachment to the lateral collateral ligament
  • meniscofemoral ligament: posterior horn to femur
  • popliteus tendon laterally
• common attachments:
  • posterior horns of both the medial and lateral menisci attach to the posterior intercondylar area of the tibial plateau
  • transverse meniscal (or genual) ligament (of Winslow) attaches the anterior horns to each other
  • joint capsule peripherally except the lateral meniscus at the site of the popliteus tendon hiatus

Blood supply

• outer one-third: supply from the peripheral meniscal plexus from medial, in turn formed from the medial, lateral and middle genicular arteries ^{6, 8}
• inner two-thirds: no vascular supply; diffusion dependent ⁶

Nerve supply

• posterior articular branch of the posterior tibial nerve and terminal obturator and femoral nerve branches ⁸

Variant anatomy

• discoid meniscus ^4-5
• congenital hypoplasia or absence ⁴
• aberrant insertion of the anterior horn of the medial menisci (2%)
  • into the ACL or intercondylar notch ⁴
  • anterior margin of the tibia in the midline ⁵
  • no attachment: stabilised by the transverse meniscal ligament ⁵
• meniscal ossicle (rare; incidence <0.2%) ⁵

Related pathology

• meniscal tear
  • absent bow tie sign
  • double PCL sign 
• meniscal flounce
• meniscal cyst