Meniscal Injuries

ANATOMY 

• elasofibrocartilagenous

• crescent shaped; triangular in cross-section

• anterior horns attached to each other by the small transverse anterior intermeniscal ligament

• lateral meniscus is more circular; medial meniscus more C-shaped

• lateral meniscus has twice the excursion of the medial meniscus during knee motion.

• anterior horn of lateral meniscus & post horns of both meniscii attach to the intercondylar eminence

• popliteus muscle (not tendon) is attached to lateral meniscus

• semimembranosis is attached to medial meniscus

• Blood supply: 

  • from branches of the lateral, middle & medial genicular arteries

  • vascular synovial tissue from the capsule supplies the peripheral third of meniscus

Frontal section of the medial compartment demonstrates the microvasculature of the medial meniscus. The perimeniscal capillary plexus (PCP) permeates through the peripheral border of the meniscus. F: Femur; T: Tibia. [Arnoczky SP, Warren RF. Microvasculature of the human meniscus. Am J Sports Med. 1982;10:90-95.]

•  Constituents:

1. Type 1 collagen fibres arranged radially & longitudinally (circumferential)

   • longitudinal fibres - dissipate hoop stresses in the meniscus

   • radial fibres & longit fibres - allows meniscii to expand under compressive force

2. Proteoglycans

   • trapped within collagen fibres to absorb energy

FUNCTION

1. Load bearing: 
   • at least 50% of the compressive load of the knee joint is transmitted through the meniscus in extension , and approx 85% of the load is transmitted in 90° flexion.
     In the meniscectomised knee the contact area is reduced approx 50%
   • Partial meniscectomy also increases the contact pressures
2. Shock absorption: 
   • menisci may attenuate the intermittent shock waves generated by impulse loading during gait- the shock absorbing capacity of normal knees is ~ 20% higher than in meniscectomised knees.
   • The ability of a system to absorb shock has been implicated in development of OA ( Radin and Rose " The role of subchondral bone in the initiation and progression of Osteoarthritis" CORR 213:34-40, 1986)
3. Knee joint stability: 
   • meniscectomy alone may not seriously affect stability. However, in assoc with ACL tears, meniscectomy increases ant laxity of the knee
4. Lubrication
5. Proprioception: 
   • this has been inferred from the finding of type 1 and type 2 nerve endings in the ant and post horns of the menisci

MENISCAL TEARS