Sports Medicine: Just the Facts

CHAPTER 58 • KNEE MENISCAL INJURIES 343

plateau (Arnoczky and McDevitt, 2000; Rath and

Richmond, 2000).

• The lateral meniscus is nearly uniform in width from
  front to back.
  •The bony attachments of the lateral meniscus are
  much closer to each other than those of the medial
  meniscus. The anterior horn inserts adjacent to the
  ACL, and the posterior horn inserts just posterior to
  the ACL, anterior to the posterior horn of the medial
  meniscus.


• There is a loose peripheral attachment of the lateral
  meniscus to the joint capsule that allows greater trans-
  lation of the lateral meniscus, when compared to the
  medial (11.2 vs. 5.2 mm) (Arnoczky and McDevitt,
  2000).


• The area of the lateral meniscus with no coronary lig-
  ament attachment, anterior to the popliteus tendon, is
  called the bare area of the lateral meniscus, or
  popliteal hiatus.

LATERAL MENISCUS ATTACHMENTS

• Motion of the lateral meniscus is guided by the cap-
  sular attachments, as well as additional ligamentous
  attachments. These ligaments include the menis-
  cofemoral ligaments, and the anterior-inferior and
  posterior-superior popliteomeniscal fascicles from the
  popliteus muscle.


• The posterior horn has variably present attachments to
  the medial femoral condyle through the menis-
  cofemoral ligaments (MFLs). The MFLs originate
  from the posterior horn of the lateral meniscus.


• The anterior MFL (of Humphrey) passes anterior to
  the posterior cruciate ligament (PCL) to insert on the
  femur between the distal margin of the femoral attach-
  ment of the PCL and the edge of the condylar articu-
  lar cartilage.


• The posterior MFL (of Wrisberg) passes posterior to
  the PCL to insert at the proximal margin of the
  femoral attachment of the PCL.


• The overall incidence of at least one MFL is 91%.
  In the knees demonstrating at least one structure,
  the incidence of an anterior MFL is 48.2%, and
  posterior MFL is 70.4%. The incidence of both lig-
  aments coexisting in one knee is 31.8% (Gupte
  et al, 2003).

MENISCAL VARIANTS

• Discoid variants occur with an estimated incidence of
  3.5–5%, most commonly the incomplete type (Greis
  et al, 2002a).
  
  
  • Discoid meniscus is almost universally located in the
    lateral compartment.
  
  
  • Three types exist—incomplete, complete, and
    Wrisberg.
  
  
  • Both the incomplete and complete types have firm
    posterior tibial attachments, and are considered stable.
  
  
  • The Wrisberg variant occurs when the posterior horn
    bony attachment is absent, and the posterior menis-
    cofemoral ligament of Wrisberg is the only stabilizing
    structure (Greis et al, 2002a).
  
  
  
  

MICROSCOPIC ANATOMY

• The menisci are fibrocartilagenous tissue comprised
  of cells interspersed in a matrix largely composed of
  collagen bundles, along with noncollagenous proteins
  including elastin, and proteoglycans.
  •Two cell types are present—a more fusiform, fibrob-
  lastic cell, and a more rounded, chondrocytic cell.
  •Water constitutes 72% of the extracellular matrix, and
  collagen makes up 75% of the dry weight (Lo et al,
  2003).


• Elastin is estimated to be less than 0.6%, and noncol-
  lagenous proteins 8–13%, of the meniscus dry weight
  in humans (Lo et al, 2003).
  •Type I collagen represents 90% of collagen present,
  and types II, III, V, and VI are present in varying quan-
  tities depending on location and age (Lo et al, 2003).


• The principle orientation of collagen fiber bundles is
  circumferential, with few radially directed “tie”
  fibers. Tie fibers provide structural rigidity to help
  resist forces that would split the circumferential fibers
  with compressive loading (Arnoczky and McDevitt,
  2000; Lo et al, 2003).


• Fiber orientation changes with depth from the surface.
  Surface fibers are arranged as a network of irregularly
  oriented bundles. The deeper fibers are primarily cir-
  cumferential (Lo et al, 2003).

NEUROVASCULAR ANATOMY

• Both medial and lateral menisci demonstrate an exten-
  sive microvascular network, arising from the respec-
  tive superior and inferior geniculate arteries (Rath and
  Richmond, 2000; Klimkiewicz and Shaffer, 2002).


• The perimeniscal capillary plexus is oriented circum-
  ferentially, and branches extensively into smaller ves-
  sels to supply the peripheral border of the meniscus
  through its attachment to the capsule.


• The branches terminate after supplying the peripheral
  10–30% of the meniscus, leaving the remainder avas-
  cular (Lo et al, 2003; Klimkiewicz and Shaffer, 2002).