The knee, the most complex synovial joint in the body
(Figure 5.16), is held together with many ligaments that
stabilize it. The sudden changes of direction of movement
or impacts to the legs that cause unnatural movements of
the joint often lead to knee injuries, especially in young ath-
letes (see
What a Health Provider Sees).
The most common
knee injury is tearing of the anterior cruciate ligament
(ACL), which occurs in about 70% of all serious knee inju-
ries. The ACL is often damaged if the knee joint is twisted
or hyperextended.
A natom y o f th e k n ee • Figure 5.16
Femur
Quadriceps
femoris
tendon
Patella
Fibular
collateral
ligament
Bursa
Fibula
Bursa reduces
friction
The knee is a synovial joint that is reinforced by several ligaments that
stabilize it in various directions. This helps prevent hyperextension and
stops the tibia from sliding around on the femur. The menisci of the
knee help even out the irregular bone surfaces and protect the articular
cartilage, while its bursae help reduce friction. Most knee injuries involve
tearing of the ligaments, especially the anterior cruciate ligament.
Tibial collateral
ligament
strengthens
medial aspect
Articular
fat pad
Patellar
ligament
strengthens anterior
surface
Tibia
Femur
Lateral
meniscus
is fibrocartilage
that evens out
irregular shapes
of the bone
surface
Tibia
Gastrocnemius
muscle
Quadriceps
femoris tendon
Patella
Articular
fat pad
Bursa
Patellar
ligament
a.
Anterior superficial
view
b. Sagittal section
Anterior cruciate
ligament (ACL)
limits hyperextension
and prevents sliding
of the tibia on femur
Lateral
Fibular
collateral
ligament
Fibula
Posterior cruciate
ligament (PCL) prevents
sliding of the tibia on femur
Medial
meniscus
smoothes out
uneven shape
of bone
Transverse
ligament
connects
menisci
Tibial
collateral
ligament
Tibia
c.
Anterior deep view
Which of the following components of
the knee prevent the femur from slid-
ing over the surface of the tibia?
a. Posterior cruciate ligament
b. Lateral meniscus
c. Anterior cruciate ligament
d. Medial meniscus
142 CHAPTER 5
The Skeletal System
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