276
UNIT TWO
S
urgeons use several synthetic materials to
replace joints severely damaged by arthri-
tis or injury. Metals such as cobalt, chro-
mium, and titanium alloys are used to replace
larger joints, whereas silicone polymers are more
commonly used to replace smaller joints. Such
artif
cial joints must be durable yet not provoke
immune system rejection. They must also allow
normal healing to occur and not move surround-
ing structures out oF their normal positions.
Ceramic materials are used in about 5% oF hip
replacements, but recipients sometimes com-
plain oF the joint squeaking.
BeFore the advent oF joint replacements,
surgeons removed damaged or diseased joint
surFaces, hoping that scar tissue f
lling in the area
would restore mobility. This type oF surgery was
rarely successFul. In the 1950s, AlFred Swanson,
an army surgeon in Grand Rapids, Michigan,
invented the First joint implants using silicone
polymers. By 1969, aFter much reFinement, the
f
rst silicone-based joint implants became avail-
able. These devices provided ±
exible hinges For
joints oF the toes, f
ngers, and wrists. Since then,
more than two dozen joint replacement models
have been developed, and more than a million
people have them, mostly in the hip.
A surgeon inserts a joint implant in a proce-
dure called implant resection arthroplasty. The
surgeon First removes the surFace oF the joint
bones and excess cartilage. Next, the centers oF
the tips oF abutting bones are hollowed out, and
the stems oF the implant are inserted here. The
hinge part oF the implant lies between the bones,
aligning them yet allowing them to bend, as they
would at a natural joint. Bone cement Fixes the
implant in place. ²inally, the surgeon repairs the
tendons, muscles, and ligaments. As the site oF
the implant heals, the patient must exercise the
joint. A year oF physical therapy may be necessary
to Fully benef
t From replacement joints.
Newer joint replacements use materials that
resemble natural body chemicals. Hip implants,
For example, may bear a coat oF hydroxyapatite,
which interacts with natural bone. Instead oF f
lling
in spaces with bone cement, some investigators
are testing a variety oF porous coatings that allow
bone tissue to grow into the implant area.
8.1
CLINICAL APPLICATION
Replacing Joints
In addition to the ligaments that strengthen the joint cap-
sule, two ligaments in the joint, called
cruciate
(kroo
she-a
¯t)
ligaments,
help prevent displacement of the articulating sur-
faces. These strong bands of F brous tissue stretch upward
between the tibia and the femur, crossing each other on the
way. They are named according to their positions of attach-
ment to the tibia. ±or example, the
anterior cruciate ligament
originates from the anterior intercondylar area of the tibia
and extends to the lateral condyle of the femur. The
posterior
cruciate ligament
connects the posterior intercondylar area
of the tibia to the medial condyle of the femur.
The young soccer player, running at Full speed, suddenly switches
direction and is literally stopped in her tracks by a popping sound
Followed by a searing pain in her knee. Two hours aFter she veered
toward the ball, her knee is swollen and painFul, due to bleeding
into the joint. She has torn the anterior cruciate ligament, a serious
knee injury.
Two F
brocartilaginous
menisci
separate the articulating
surfaces of the femur and tibia and help align them. Each
meniscus is roughly
C
-shaped, with a thick rim and a thin-
ner center, and attaches to the head of the tibia. The medial
and lateral menisci form depressions that F
t the correspond-
ing condyles of the femur (F
g. 8.21).
Several bursae are associated with the knee joint. These
include a large extension of the knee joint cavity called the
suprapatellar bursa,
located between the anterior surface
of the distal end of the femur and the muscle group (quad-
riceps femoris) above it; a large
prepatellar bursa
between
The
joint capsule
of the knee is relatively thin, but liga-
ments and the tendons of several muscles greatly strengthen
it. ±or example, the fused tendons of several muscles in the
thigh cover the capsule anteriorly. ±ibers from these tendons
descend to the patella, partially enclose it, and continue
downward to the tibia. The capsule attaches to the margins
of the femoral and tibial condyles as well as between these
condyles
(f g. 8.20)
.
The ligaments associated with the joint capsule that help
keep the articulating surfaces of the knee joint in contact
include the following
(f
g. 8.21)
:
1.
Patellar
(pah-tel
ar)
ligament.
This ligament is a
continuation of a tendon from a large muscle group in
the thigh (quadriceps femoris). It consists of a strong,
fl at band that extends from the margin of the patella to
the tibial tuberosity.
2.
Oblique popliteal
(o
˘
ble
¯k pop-lit
e-al)
ligament.
This
ligament connects the lateral condyle of the femur to the
margin of the head of the tibia.
3.
Arcuate
(ar
ku-a
¯t)
popliteal ligament.
This ligament
appears as a
Y
-shaped system of F
bers that extends
from the lateral condyle of the femur to the head of the
F bula.
4.
Tibial collateral
(tib
e-al ko
˘-lat
er-al)
ligament
(medial
collateral ligament). This ligament is a broad, fl
at band
of tissue that connects the medial condyle of the femur
to the medial condyle of the tibia.
5.
Fibular
(F b
u-lar)
collateral ligament
(lateral collateral
ligament). This ligament consists of a strong, round cord
located between the lateral condyle of the femur and the
head of the F
bula.
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