Meniscus

Question 1

Menisci of the knee joint (intra-articular discs)

Answer 1

• the medial meniscus + lateral meniscus are fibrocartilaginous crescent-shaped structures located b/w the femoral condyles + their attachments to the tibial plateaus
• Medial meniscus on the longer tibial plateau is more C-shaped (more oval), while the lateral meniscus is more semi-circle shaped (rounder)
• Cover >50% of each tibial plateau
• Ligament (static) attachments include:
  
  • Medially: deep fibres of the MCL
  • Posteriorly: posterior meniscofemoral ligament

Question 2

Meniscus structure

Answer 2

• Wedge-shaped (narrower centrally)
• Mostly circumferential collagen fibres – allows dispersion of compressive loads
• Radial superficial fibres – help to resist longitudinal tearing
• Superficial ‘mesh’ structure – distributes shear stress

Question 3

Meniscus functions

Answer 3

Main functions include:
- reduce friction/aid in joint lubrication
- absorb forces (shock)
- increase joint congruency
- assist in WB role
- participate in knee locking mechanism
- proprioceptive role

• The medial meniscus is more stable than the lateral meniscus due to firm connections with the MCL + joint capsule = makes it more prone to injury

Question 4

Menisci nerve and blood supply

Answer 4

• Only the peripheral part of an adult meniscus is innervated (proprioceptive role). - The central part is aneural.
• Both the central + peripheral parts of a child’s meniscus are vascular i.e. have a blood supply.
• With increasing age, the central part of a meniscus becomes progressively avascular (hence is less likely to regenerate if torn).

Question 5

Menisci movements

Answer 5

• Slight distortion/motion of the menisci occurs to keep them in a suitable position to reduce friction + absorb motion during knee flexion + extension
• During knee flexion, posterior motion is assisted by muscles:
  
  • Medial meniscus – semimembranosus
  • Lateral meniscus - popliteus

Question 6

Menisci movements during tibial rotation

Answer 6

• During external tibial rotation, the lateral meniscus is pulled anteriorly, the medial meniscus posteriorly
• During internal tibial rotation, the lateral meniscus is pulled posteriorly, the medial meniscus anteriorly.
• Menisci are most vulnerable to damage during rotational movts, especially combined w/ axial load through a flexed knee (e.g. soccer, skiing, basketball)
• Common with ACL laxity or injury (trauma)
• Due to reduced vascularity in the adult, tears of menisci may also be degenerative + often need surgical repair