The menisci of the knee play several important roles. They improve tibiofemoral congruence, distribute weight-bearing forces to reduce friction and act as shock absorbers. The medial meniscus is C-shaped while the lateral is four-fifths circular. Both are thicker peripherally and thinner centrally. The medial meniscus covers less of the tibial plateau and has greater ligamentous restraints. The menisci receive nutrition through blood vessels in the periphery but rely on synovial fluid diffusion centrally. They are well innervated in the periphery to detect pain and proprioception.

1. Biomechanics
of the
Knee Complex : 2
DR. DIBYENDUNARAYAN BID [PT]
THE SARVAJANIK COLLEGE OF PHYSIOTHERAPY,
RAMPURA, SURAT

2. Menisci
 Tibiofemoral congruence is improved by the medial and
lateral menisci, forming concavities into which the
femoral condyles sit (Fig. 11-8).
 In addition to enhancing joint congruence, these
accessory joint structures play an important role in
distributing weight-bearing forces, in reducing friction
between the tibia and the femur, and in serving as shock
absorbers.
 The menisci are fibrocartilaginous disks with a
semicircular shape.

3.  The medial meniscus is C-shaped, whereas the lateral
meniscus forms four fifths of a circle.8 Lying within the
tibiofemoral joint, the menisci are located on top of the
tibial condyles, covering one half to two thirds of the
articular surface of the tibial plateau (Fig. 11-9).
 Both menisci are open toward the intercondylar
tubercles, thick peripherally and thin centrally. The
lateral meniscus covers a greater percentage of the
smaller lateral tibial surface than the medial meniscus.

4.  As a result of its larger exposed surface, the medial
condyle has a greater susceptibility to the enormous
compressive loads that pass through the medial
condyle during routine daily activities.
 Although compressive forces in the knee may reach
one to two times body weight during gait and stair
climbing and three to four times body weight during
running, the menisci assume 50% to 70% of this
imposed load.

5.  These loads, however, can be influenced by the
presence of frontal plane malalignment.
 The greater the degree of genu varum, for instance,
the greater is the compression on the medial
meniscus.

6. Meniscal Attachments
 The open anterior and posterior ends of the menisci
are called the anterior and posterior horns, each of
which is firmly attached to the tibia below.
 Meniscal motion on the tibia is consequently limited
by multiple attachments to surrounding structures,
some common to both menisci and some unique to
each.

8.  The medial meniscus has greater ligamentous and
capsular restraints, limiting translation to a greater
extent than the lateral meniscus.
 The relative lack of mobility of the medial meniscus
may contribute to its greater incidence of injury.

10.  Anteriorly, the menisci are connected to each other by the
transverse ligament.
 Both menisci are also attached directly or indirectly to the
patella via the patellomeniscal ligaments, which are
anterior capsular thickenings.
 At the periphery, the menisci are connected to the tibial
condyle by the coronary ligaments, which are composed of
fibers from the knee joint capsule.
 Some of these connections can be seen in Figure 11-9.

11.  The medial meniscus has less relative motion than
does the lateral meniscus, and it is more firmly
attached to the joint capsule through medial
thickening of the joint capsule that extends distally
from the femur to the tibia.
 This capsular thickening, referred to as the deep
portion of the medial collateral ligament (MCL),
further restricts the motion of the medial meniscus.

12.  The anterior and posterior horns of the medial meniscus
are attached to the anterior cruciate ligament (ACL) and
posterior cruciate ligament (PCL), respectively.
 Through capsular connections, the semimembranosus
muscle connects to the medial meniscus.
 Posteriorly, the lateral meniscus attaches to the PCL and
the medial femoral condyle through the meniscofemoral
ligaments.

13.  Some of the ligamentous attachments are shown in
Figure 11-10.
 In much the same way that the semimembranosus
tendon is attached to the medial meniscus, the
tendon of the popliteus muscle attaches to the lateral
meniscus.
 The attachment to the popliteus tendon helps
restrain or control the motion of the lateral
meniscus.

15. Role of the Menisci
 The strong attachments to the menisci prevent them
from being squeezed out during compression of the
tibiofemoral joint, allowing for greater contact area
between the menisci and the femur.
 If the femoral condyles sat directly on the relatively
flat tibial plateau, there would be little contact
between the bony surfaces.

16.  With the addition of the menisci, the contact at the
tibiofemoral joint is increased and joint stress (force
per unit area) is, therefore, reduced on the joint’s
articular cartilage (Fig. 11-11).

18.  After the removal of a meniscus, the contact area in
the tibiofemoral joint is decreased, which thus
increases joint stress.
 Specifically, removal of the menisci nearly doubles
the articular cartilage stress on the femur and
multiplies the forces by six or seven times on the
tibial plateau.
 The increase in joint stress may contribute to
degenerative changes within the tibiofemoral joint.

19.  For this reason, total meniscectomies are rarely
performed after a meniscal tear; instead, care is
taken to preserve as much of the meniscus as
possible, either through débridement (removal of
damaged tissue) or repair.

20. Meniscal Nutrition and Innervation
 The location of a meniscal lesion and the age of the
patient influence the options available after injury
because of the capacity of the meniscus to heal.
 During the first year of life, the meniscus contains
blood vessels throughout the meniscal body.
 Once weight-bearing is initiated, vascularity begins
to diminish until only the outer 25% to 33% is
vascularized by capillaries from the joint capsule and
the synovial membrane.

21.  After 50 years of age, only the periphery of the
meniscal body is vascularized.
 Therefore, the peripheral portion obtains its
nutrition through blood vessels, but the central
portion must rely on the diffusion of synovial fluid.

22.  The process of fluid diffusion to support nutrition
requires intermittent loading of the meniscus by
either weight-bearing or muscular contractions.
 Subsequently, during prolonged periods of
immobilization or conditions of non–weight-bearing,
the meniscus may not receive appropriate nutrition.

23.  The avascular nature of the central portion of the
meniscus reduces the potential for healing after an
injury.
 In adults, only the peripheral vascularized region of
the meniscus is capable of inflammation, repair, and
remodeling after a tearing injury.

24.  The horns of the menisci and the peripheral
vascularized portion of the meniscal bodies are well
innervated with free nerve endings (nociceptors) and
three different mechanoreceptors (Ruffini
corpuscles, pacinian corpuscles, and Golgi tendon
organs).
 The presence of nociceptors in the meniscus could
explain some of the pain felt by patients after a
meniscal tear, at least for tears located in the
periphery.

25.  Proprioceptive deficits may potentially occur after
meniscal injury as a result of injury to the
mechanoreceptors within the meniscus.

26. End of Part - 2