Chapter 8
Joints
263
8
knee and are stretched taut when the knee is extended. Tese
include the following:
Te extracapsular
fibular
and
tibial collateral ligaments
are
also critical in preventing lateral or medial rotation when the
knee is extended. Te broad, flat tibial collateral ligament
runs from the medial epicondyle of the femur to the medial
condyle of the tibial shaF below and is fused to the medial
meniscus (±igure 8.8c–e).
Te
oblique popliteal ligament
(pop
0
lĭ-te
9
al) is actually part
of the tendon of the semimembranosus muscle that fuses
with the joint capsule and helps stabilize the posterior aspect
of the knee joint (±igure 8.8d).
Te
arcuate popliteal ligament
arcs superiorly from the
head of the fibula over the popliteus muscle and reinforces
the joint capsule posteriorly (±igure 8.8d).
Te knee’s
intracapsular ligaments
are called
cruciate liga-
ments
(kroo
9
she-āt) because they cross each other, forming an
X (
cruci
5
cross) in the notch between the femoral condyles.
Tey act as restraining straps to help prevent anterior-posterior
displacement of the articular surfaces and to secure the articu-
lating bones when we stand (±igure 8.8a, b, e). Although these
ligaments are in the joint capsule, they are
outside
the syno-
vial cavity, and synovial membrane nearly covers their surfaces.
Note that the two cruciate ligaments both run superiorly to the
femur and are named for their
tibial
attachment site.
Te
anterior cruciate ligament
attaches to the
anterior
inter-
condylar area of the tibia (±igure 8.8b). ±rom there it passes pos-
teriorly, laterally, and upward to attach to the femur on the medial
side of its lateral condyle. Tis ligament prevents forward sliding
of the tibia on the femur and checks hyperextension of the knee. It
attached only at their outer margins and are frequently torn free.
Te tibiofemoral joint acts primarily as a hinge, permitting flex-
ion and extension. However, structurally it is a bicondylar joint.
Some rotation is possible when the knee is partly flexed, and when
the knee is extending. But, when the knee is fully extended, side-to-
side movements and rotation are strongly resisted by ligaments and
the menisci. Te femoropatellar joint is a plane joint, and the patella
glides across the distal end of the femur during knee flexion.
Te knee joint is unique in that its joint cavity is only par-
tially enclosed by a capsule. Te relatively thin articular cap-
sule is present only on the sides and posterior aspects of the
knee, where it covers the bulk of the femoral and tibial condyles.
Anteriorly, where the capsule is absent, three broad ligaments
run from the patella to the tibia below. Tese are the
patellar
ligament
flanked by the
medial
and
lateral patellar retinacula
(ret
0
ĭ-nak
9
u-lah; “retainers”), which merge imperceptibly into
the articular capsule on each side (±igure 8.8c). Te patellar lig-
ament and retinacula are actually continuations of the tendon
of the bulky quadriceps muscle of the anterior thigh. Physicians
tap the patellar ligament to test the knee-jerk reflex.
Te synovial cavity of the knee joint has a complicated shape,
with several extensions that lead into “blind alleys.” At least a dozen
bursae are associated with this joint, some of which are shown
in ±igure 8.8a. ±or example, notice the
subcutaneous prepatellar
bursa
, which is oFen injured when the knee is bumped anteriorly.
All three types of joint ligaments stabilize and strengthen the
capsule of the knee joint. Te ligaments of two of the types, cap-
sular and extracapsular, all act to prevent hyperextension of the
Fibular
collateral
ligament
Posterior
cruciate
ligament
Medial
condyle
Tibial
collateral
ligament
Anterior
cruciate
ligament
Medial
meniscus
Patellar
ligament
Patella
Quadriceps
tendon
Lateral
condyle
of femur
Lateral
meniscus
Fibula
(e) Anterior view of flexed knee, showing the cruciate ligaments
(articular capsule removed, and quadriceps tendon cut
and reflected distally)
Tibia
Medial femoral condyle
Anterior cruciate ligament
Medial meniscus on
medial tibial condyle
Patella
(f) Photograph of an opened knee joint; view similar to (e)
Figure 8.8
(continued)
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