The Knee and Patellofemoral Joints 243The Menisci
The menisci (G. meniskos, crescent)—the medial
meniscus and lateral meniscus—are two fibrocartilage
discs that sit on the tibial plateau and form the articu-
lar surface for the respective medial and lateral con-
dyles of the femur as seen in figure 5.4. These menisci
are thicker around their perimeter than centrally, and
so form a kind of collar that aids in joint integrity by
increasing the depth and fit of the articulation. The
inferior surfaces of the menisci are flat to contour
to the tibial plateaus, whereas the superior surfaces
are concave to conform to the shape of the femoral
condyles. By helping to overcome the difference in
contour between the articulating femoral condyles
and tibial condyles, and providing more surface area
of contact between these bones, the menisci also help
absorb shock, decrease frictional wear, and facilitate
knee movements. Furthermore, due to the properties
of cartilage (viscoelastic properties), when they are
loaded they further increase the contact area and
decrease joint stresses—approximately doubling the
contact area in the joint and bearing as much as 45%
of the total load absorbed by the knee (Hall, 1999;
Hamill and Knutzen, 1995; Soderberg, 1986). More-
over, the further separation of the joint surfaces they
provide allows for greater lubrication of the joint, and
a 20% increase in friction has been demonstrated to
occur with removal of the meniscus. The vital impor-
tance of the menisci is evidenced by the tendency for
early degenerative changes in knees where a menis-
cus has been surgically removed due to injury.
The medial meniscus is larger in circumference
than the lateral and is “C” shaped, barely forming a
semicircle. The lateral meniscus is more “O” shaped,
almost forming a complete circle, except where it
attaches to the intercondylar area. The medial and
lateral menisci are joined to each other anteriorly
via the transverse ligament. The menisci are joined
to the tibia anteriorly at the anterior intercondylar
area, posteriorly at the posterior intercondylar area,
and by vertical fibers of the coronary ligaments along
their periphery to the edges of the tibial condyles.
The inner borders, superior surface, and inferior
surface of the menisci are free. The medial meniscus
is also securely attached to the medial collateral liga-
ment and one of the medial hamstring muscles (the
semimembranosus), making the medial meniscus
less freely movable than the lateral. During knee
flexion, the menisci move posteriorly with the femur,
with the more movable lateral meniscus traveling
approximately twice as far (0.4 vs. 0.2 inches [11 vs. 5
millimeters]) as the medial (Dye and Vaupel, 2000).
During knee extension, the menisci move anteriorly
with the femur. Perhaps partly due to its firmer
attachments and more restricted movement, the
medial meniscus is much more frequently injured
than the lateral meniscus (Caillet, 1996).Bursae
More than 20 bursae are commonly present around
the knee joint (Hamill and Knutzen, 1995). For exam-
ple, as illustrated in figure 5.5, one bursa lies beneath
the distal tendons of a group of muscles key for medialFIGURE 5.4 The menisci and selected associated
structures (right knee, superior view).