270
UNIT 2
Covering, Support, and Movement of the Body
8
Current theory holds that normal joint use prompts the re-
lease of (metalloproteinase) enzymes that break down articular
cartilage, especially its collagen fibrils. In healthy individuals,
this damaged cartilage is eventually replaced, but in people with
OA, more cartilage is destroyed than replaced. Although its spe-
cific cause is unknown, OA may reflect the cumulative effects of
years of compression and abrasion acting at joint surfaces, caus-
ing excessive amounts of the cartilage-destroying enzymes to be
released. Te result is soFened, roughened, pitted, and eroded
articular cartilages. Because this process occurs most where
an uneven orientation of forces cause extensive microdamage,
badly aligned or overworked joints are likely to develop OA.
As the disease progresses, the exposed bone tissue thickens
and forms bony spurs (osteophytes) that enlarge the bone ends
and may restrict joint movement. Patients complain of stiff-
ness on arising that lessens somewhat with activity. Te affected
joints may make a crunching noise, called
crepitus
(krep
9
ĭ-tus),
as they move and the roughened articular surfaces rub together.
Te joints most oFen affected are those of the cervical and lum-
bar spine and the fingers, knuckles, knees, and hips.
Te course of osteoarthritis is usually slow and irreversible.
In many cases, its symptoms are controllable with a mild pain
reliever like aspirin or acetaminophen, along with moderate ac-
tivity to keep the joints mobile. Rubbing a hot-pepper substance
called capsaicin on the skin over the painful joints helps lessen
the pain of OA. Glucosamine and chondroitin sulfate, nutritional
supplements consisting of macromolecules normally present in
cartilage, have been widely used by arthritis sufferers. However,
several recent studies suggest that these supplements are no more
effective than placebos. Osteoarthritis is rarely crippling, but it
can be, particularly when the hip or knee joints are involved.
Rheumatoid Arthritis
Rheumatoid arthritis (RA)
(roo
9
mah-
toid) is a chronic inflammatory disorder with an insidious on-
set. Tough it usually arises between the ages of 30 and 50, it
may occur at any age. It affects three times as many women as
men. While not as common as osteoarthritis, rheumatoid ar-
thritis affects millions, about 1% of all people.
In the early stages of RA, joint tenderness and stiffness are com-
mon. Many joints, particularly the small joints of the fingers, wrists,
ankles, and feet, are afflicted at the same time and bilaterally. ±or
example, if the right elbow is affected, most likely the leF elbow is
also affected. Te course of RA is variable and marked by flare-ups
(exacerbations) and remissions (
rheumat
5
susceptible to change).
Along with pain and swelling, its manifestations may include ane-
mia, osteoporosis, muscle weakness, and cardiovascular problems.
RA is an
autoimmune disease
—a disorder in which the
body’s immune system attacks its own tissues. Te initial trigger
for this reaction is unknown, but various bacteria and viruses
have been suspect. Perhaps these microorganisms bear mol-
ecules similar to some naturally present in the joints (possibly
glycosaminoglycans, which are complex carbohydrates found
in cartilage, joint fluid, and other connective tissues), and the
immune system, once activated, attempts to destroy both.
RA begins with inflammation of the synovial membrane
(
synovitis
) of the affected joints. Inflammatory cells (lym-
phocytes, macrophages, and others) migrate into the joint cavity
from the blood and unleash a deluge of inflammatory chemicals
Certain ligaments, like the anterior cruciate ligament, are
best repaired by replacing them with graFs. ±or example, a
piece of tendon from a muscle can be attached to the articu-
lating bones.
±or many ligaments, such as the knee’s medial collateral liga-
ment, we’ve come to realize that time and immobilization are
just as effective as any surgical option.
Dislocations
A
dislocation (luxation)
occurs when bones are forced out of
alignment. It is usually accompanied by sprains, inflammation,
and difficulty in moving the joint. Dislocations may result from
serious falls and are common contact sports injuries. Joints of
the jaw, shoulders, fingers, and thumbs are most commonly dis-
located. Like fractures, dislocations must be
reduced
; that is, the
bone ends must be returned to their proper positions by a phy-
sician.
Subluxation
is a partial dislocation of a joint.
Repeat dislocations of the same joint are common because the
initial dislocation stretches the joint capsule and ligaments. Te
resulting loose capsule provides poor reinforcement for the joint.
Inflammatory and Degenerative Conditions
Inflammatory conditions that affect joints include bursitis and
tendonitis, various forms of arthritis, and Lyme disease.
Bursitis and Tendonitis
Bursitis
is inflammation of a bursa and is usually caused by a blow
or friction. ±alling on one’s knee may result in a painful bursitis of
the prepatellar bursa, known as
housemaid’s knee
or
water on the
knee
. Prolonged leaning on one’s elbows may damage the bursa
close to the olecranon, producing
student’s elbow
, or
olecranon
bursitis
. Severe cases are treated by injecting anti-inflammatory
drugs into the bursa. If excessive fluid accumulates, removing
some fluid by needle aspiration may relieve the pressure.
Tendonitis
is inflammation of tendon sheaths, typically caused
by overuse. Its symptoms (pain and swelling) and treatment (rest,
ice, and anti-inflammatory drugs) mirror those of bursitis.
Arthritis
Te term
arthritis
describes over 100 different types of inflam-
matory or degenerative diseases that damage the joints. In all
its forms, arthritis is the most widespread crippling disease in
North America. One in five of us suffers its ravages. ²o a greater
or lesser degree, all forms of arthritis have the same initial symp-
toms: pain, stiffness, and swelling of the joint.
Acute forms of arthritis usually result from bacterial inva-
sion and are treated with antibiotics. Chronic forms of arthritis
include osteoarthritis, rheumatoid arthritis, and gouty arthritis.
Osteoarthritis
Osteoarthritis (OA)
is the most common chronic
arthritis. A chronic (long-term) degenerative condition, OA is of-
ten called “wear-and-tear arthritis.” OA is most prevalent in the
aged and is probably related to the normal aging process (although
it is seen occasionally in younger people and some forms have a
genetic basis). More women than men are affected, but nearly half
of us will develop this condition by the age of 85.
previous page 304 Human Anatomy and Physiology (9th ed ) 2012 read online next page 306 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off