Chapter 8
Joints
269
8
Cartilage Tears
Many aerobics devotees, encouraged to “feel the burn” during
their workout, may feel the snap and pop of their overstressed
cartilage instead. Although most cartilage injuries involve tear-
ing of the knee menisci, tears and overuse damage to the articu-
lar cartilages of other joints is becoming increasingly common
in competitive young athletes.
Cartilage tears typically occur when a meniscus is subjected to
compression and shear stress at the same time. Cartilage is avascular
and it rarely can obtain sufficient nourishment to repair itself, so
it usually stays torn. Cartilage fragments (called loose bodies) can
interfere with joint function by causing the joint to lock or bind, so
most sports physicians recommend that the damaged cartilage be
removed. Today, this can be done by
arthroscopic surgery
(ar-thro-
skop
9
ik; “looking into joints”), a procedure that enables patients to
be out of the hospital the same day. ±e arthroscope, a small instru-
ment bearing a tiny lens and fiber-optic light source, enables the sur-
geon to view the joint interior, as in
Figure 8.14
. ±e surgeon can
then repair a ligament, or remove cartilage fragments through one
or more tiny slits, minimizing tissue damage and scarring. Removal
of part of a meniscus does not severely impair knee joint mobility,
but the joint is definitely less stable. Removal of the entire meniscus is
an invitation to early onset of osteoarthritis in the joint. For younger
patients a meniscal transplant may be an option to replace irrepara-
bly damaged cartilage. In the future, a tissue-engineered meniscus
grown from your own stem cells may be implanted instead.
Sprains
In a
sprain
, the ligaments reinforcing a joint are stretched or
torn. Common sites of sprains are the ankle, the knee, and the
lumbar region of the spine. Partially torn ligaments will repair
themselves, but they heal slowly because ligaments are so poorly
vascularized. Sprains tend to be painful and immobilizing.
When ligaments are completely torn, there are three options:
±e torn ends of the ligament can be sewn together. ±is is dif-
ficult because trying to sew the hundreds of fibrous strands of a
ligament together is like trying to sew two hairbrushes together.
a side-to-side movement called
lateral excursion
(Figure 8.13c).
±is lateral jaw movement is unique to mammals and it is readily
apparent in horses and cows as they chew.
Homeostatic Imbalance
8.2
Because of its shallow socket, the TMJ is the most easily dislo-
cated joint in the body. Even a deep yawn can dislocate it. ±is
joint almost always dislocates anteriorly, the condylar process of
the mandible ending up in a skull region called the
infratempo-
ral fossa
(Figure 8.13a). In such cases, the mouth remains wide
open. To realign a dislocated TMJ, the physician places his or
her thumbs in the patient’s mouth between the lower molars
and the cheeks, and then pushes the mandible inferiorly and
posteriorly.
At least 5% of Americans suffer from painful temporoman-
dibular disorders, the most common symptoms of which are
pain in the ear and face, tenderness of the jaw muscles, pop-
ping sounds when the mouth opens, and joint stiffness. Usually
caused by painful spasms of the chewing muscles, TMJ disorders
o²en afflict people who grind their teeth; however, it can also re-
sult from jaw trauma or from poor occlusion of the teeth. Treat-
ment usually focuses on getting the jaw muscles to relax by using
massage, applying moist heat or ice, muscle-relaxant drugs, and
adopting stress reduction techniques. For tooth grinders, use of a
bite plate during sleep is generally recommended.
Check Your Understanding
11.
Of the five joints studied in more detail—hip, shoulder,
elbow, knee, and temporomandibular—which two have
menisci? Which act mainly as a uniaxial hinge? Which
depend mainly on muscles and their tendons for stability?
For answers, see Appendix H.
Homeostatic Imbalances
of Joints
Name the most common joint injuries and discuss the
symptoms and problems associated with each.
Compare and contrast the common types of arthritis.
Describe the cause and consequences of Lyme disease.
Few of us pay attention to our joints unless something goes
wrong with them. Although remarkably strong, joints are more
likely to be injured by forces the bony skeleton can withstand.
±is is the price of our flexibility. Joint pain and malfunction
can be caused by a number of factors besides traumatic injury,
including inflammatory conditions and degenerative processes
due to friction and wear.
Common Joint Injuries
For most of us, sprains and dislocations are the most common
trauma-induced joint injuries, but cartilage injuries are equally
threatening to athletes.
Tear in
meniscus
Femur
Meniscus
Tibia
Figure 8.14
Arthroscopic photograph of a torn medial
meniscus.
(Courtesy of the author’s tennis game.)
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