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Joints:
n

A joint is the point of contact between two bones, between
bone and cartilage, or between bone and teeth. Joints con­
tribute to homeostasis by holding bones together in ways
· that allow for movement and flexibility. With fibrous joints,

. bones are held together by dense irregular connective tissue,

0

lnterosseous
membrane·.

A fibrous joint

‘–~– Periosteum

· rich in collagen fibers. Cartilaginous joints hold bones
together with by cartilage. Synovial joints have a synovial
cavity, which is a space bernieffithe articulating bones. They
are united by the dense irregular connective tissue of an
articular capsule, and often by accessory ligaments .

Eplphyseal (growth)
plates

Epiphysis —-

Pubic—-­
symphysis ·

Epiphysis

Synchondrosis

Cartilaginous joints

Articular Ooint)
capsule:

Articulating —-­
bone

Synovial ijolnt)
cavity (contains
synovlal fluid)

Articular –­
cartilage

Articulating –­
bone·

. ‘ \_J

Typical synovlal Joint .

Fibrous
membrane

Synoviai’
membrane

. ‘

. ‘

Tests, Procedures, and Techniques

111 Arthroplasty
Joints that have been severely damaged by diseases such
as arthritis, or by injury, may be replaced surgically with
artificial joints in a procedure referred to as arthroplasty
(AR-thrii-plas’ -te; arthr- = joint; -plast:y = plastic repair

· of). Although most joints in the body .can:b·e repaired by
arthroplasty, the ones most commonly replaced are the
hips, knees, and shonlders. About 400,000 hip replace­
ments and about 300,000 knee replacements are per­
formed annually in the United States. During the pro­
cedure, the ends of the damaged bones are removed and
metal, ceramic, or plastic components are fixed in place.
The goals of arthroplasty are to relieve pain and increase
range of motion.

Partial hip replacements involve only the femnr. Total
hip replacements involve both the acetabulum and head
of the femur. The damaged portions of the acetabulum and
the head of the femur are replaced by prefabricated prosthe­
ses (artificial devices). The acetabulum is shaped to accept
the new socket, the head of the femur is removed, and the
center of the femur is shaped to fit the femoral component.
The acetabular component consists of a plastic such as
polyethylene, and the femoral component is composed of
a metal such as cobalt-chrome, titanium alloys, or stain­
less steel. These materials are designed to withstand a high
degree of stress and to prevent a response by the immune
system. Once the appropriate acetabular and femoral com­
ponents are selected, they are attached to the healthy por­
tion of bone with acrylic cement, which forms an interlock­
ing mechanical bond.

Hip bone

Reshaped
acetabulum

— Head of femur
removed

Shaft of femur

Tests, Procedures, and Techniques 31

Knee replacements are actually a resurfacing of carti­
lage and, like hip replacements, may be partial or total. In a
total knee replacement, the damaged cartilage is removed o
from the distal end of the femur, proximal end of the tibia,
and the back surface of the patella (if the back surface of
the patella is not badly damaged, it may be lefr intact). The
· femur is reshaped and fitted with a metal femoral com­
ponent and cemented in place. The tibia is reshaped and
fitted with a plastic tibia component that is cemented in
place. If the back surface of the patella is badly damaged, it
is replaced with a plastic implant.

In a partial knee replacement, also called a nnicom­
partmental knee replacement, only one side of the knee
joint is replaced. Once the damaged cartilage is removed
from the distal end of the femur, the femur is reshaped and
a metal femoral component is cemented in place. Then
the damaged cartilage from the proximal end of the tibia
is removed, along with the meniscus. The tibia is reshaped
and fitted with a plastic tibial component that is cemented
into place.

Researchers are continually seeking to improve the
strength of the cement and devise ways to stimulate bone
growth around the implanted area. Potential complica­
tions of arthroplasty include infection, blood clots, loos­
ening or dislocation of the replacement components, and
nerve injury.

In a partial knee replacement, also called a unicom­
partmental knee replacement, only one side of the knee
joint is replaced. Once the damaged cartilage is removed 0
from the distal end of the femur, the femur is reshaped and
a metal femoral component is cemented in place. Then
the damaged cartilage from the proximal end of the tibia

Artificial
acetabulum

Artificial
femoral
head

Artificial
metal shaft

Hip bone

Artificial
acetabulum
Artificial
femoral ·
head

Artificial
metal shaft

Shaft of
femur

Preparation for total hip replacement Compoiients of an artificial hip joint Radiograph of an artificial hip joint 0

n

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32 5 Joints

Femoral surfaces
removed

Tibial surfaces
removed

Patellar surface
removed

Preparation for total knee replacement

Plastic spacer

~
-i .. te ..

Femoral component Tibial component Patellar component

Femur

Femoral component

Tibial component

Tibia

Components of artificial knee joint_ (isolated and in place)

Fibula

Radiograph of a total knee replacement

is removed, along with the meniscus. The tibia is reshaped
and fitted with a plastic tibial component that is cemented
into place. .

Researchers are continually seeking to improve the
strength of the cement and devise ways to stimulate bone
growth around the implanted area. Potential complica­
tions of arthroplasty include infection, blood clots, loos­
ening or dislocation of the replacement components, and
nerve injury.

• Torn Cartilage and Arthroscopy
The tearing of articular discs (menisci) in the knee,
commonly called tom cartilage, occurs often among
athletes. Such damaged cartilage will begin to wear and
may cause arthritis to develop unless the cartilage is
surgically removed by a procedure called a menisectomy
(men’ -i-SEK-t6-me). Surgical repair of the torn cartilage
is required because of the avascular nature of cartilage
and may be assisted -by arthros<;opy (ar-THROS- ko­
pe; -scopy = observation), the visual examination of the
interior of a joint, usually the knee, with an arthroscope,
a lighted, pencil-thin instrument. Arthroscopy is used
to determine the nature and extent of damage following
knee injury and to monitor the progression of disease and

the effects of therapy. The insertion of surgical instru­
ments through the arthroscope or other incisions enables
a physician to remove torn cartilage and repair damaged
cruciate ligaments in the knee; to remodel poorly formed
cartilage; to obtain tissue samples for analysis; and to per­
form surgery on other joints, such as the shoulder, elbow,
ankle, and wrist. Ill

Arthroscopy

Disorders Affecting Joints

Ill! Ankylosing Spondylitis
Ankylosing spondylitis (ang’ -ki-LO-sing spon’ -di-LI­
tis; ankyle = stiff; spondyl = vertebra) is an inflammatory
disease of unknown origin that affects joints between ver­
tebrae (intervertebral) and between the sacrum and hip
bone (sacroiliac joint). The disease, which is more com­
mon in males, sets in between ages 20 and 40. It is char­
acterized by pain and stiffness in the hips and lower back
that progress upward along the backbone. Inflammation
can lead to ankylosis (severe or complete loss of movement
at a joint) and kyphosis (hunchback). Treatment consists of
anti-inflammatory drugs, heat, massage, and supervised
exercise.

!i\’l Bursitis
An acute or chronic inflammation of a bursa, called bursi­
tis, is usually caused by irritation from repeated, excessive
exertion of a joint. The condition may also be caused by
trauma, by an acute or chronic infection (including syphilis
and tuberculosis), or by rheumatoid arthritis. Symptoms
include pain, swelling, tenderness, and limited movement.
Treatment may include oral anti-inflammatory agents and
injections of cortisol-like steroids.

Gouty Arthritis
Uric acid (a substance that gives urine its name) is a waste
product produced during the metabolism of nucleic acid
(DNA and RNA) subunits. A person who suffers from
gout (GOWT) either produces excessive amounts of uric
acid or is not able to excrete as much as normal. The result
is a buildup of uric acid in the blood. This excess acid then
reacts with sodium to form a salt called sodium urate.
Crystals of this salt accumulate in soft tissues such as the
kidneys and in the cartilage of the ears and joints.

In gouty arthritis, sodium urate crystals are deposited
in the soft tissues of the joints. Gout most often affects the
joints of the feet, especially at the base of the big toe. The
crystals irritate and erode the cartilage, causing inflam­
mation, swelling, and acute pain. Eventually, the crystals _
destroy all joint tissues. If the disorder is untreated, the
ends of the articulating bones fuse, and the joint becomes
immovable. Treatment consists of pain relief (ibuprofen,
naproxen, colchicine, and cortisone) followed by admin­
istration of allopurinol to keep uric acid levels low so that
crystals do not form.

Ill Lyme Disease
A spiral-shaped bacterium called Borrelia burgdo,feri causes
Lyme disease, named for the town of Lyme, Connecticut,
where it was first reported in 197 5. The bacteria are trans­
mitted to humans mainly by deer. ticks. {Ixodes dammim).
These ticks are so small that their bites often go urmoticed.
Within a few weeks of the tick bite, a rash may appear at
the site. Although the rash often resembles a bull’s-eye
target, there are many variations, and some people never

Disorders Affecting Joints 33

develop a rash. Other symptoms include joint stiffness,
fever and chills, headache, stiff neck, nausea, and low back
pain. In advanced stages of the disease, arthritis is the main o
complication. It usually afflicts the larger joints such as the _
knee, ankle, hip, elbow, or wrist. Antibiotics are generally
effective against Lyme disease, especially if they are given
promptly. However, some symptoms may linger for years.

ilil Osteoarthritis ·· ··
Osteoarthritis (OA) (os’-te-ii-ar-THRI-tis) is a degen­
erative joint disease in which joint cartilage is gradually
lost. It results from a combination of aging, obesity, irrita­
tion of the joints, muscle weakness, and wear and abrasion.
Commonly known as “wear-and-tear” arthritis, osteoar­
thritis is the most common type ohrthritis.

Osteoarthritis is a progressive disorder of synovial joints,
particularly weight-bearing joints. Articular cartilage dete­
riorates and new bone forms in the subchondral areas and at
the margins of the joint. The cartilage slowly degenerates,
and as the bone ends become exposed, spurs (small bumps)
of new osseous tissue are deposited on them in a misguided
effort by the body to protect against the friction. These
spurs decrease the space of the joint cavity and restrict joint
movement. Unlike rheumatoid arthritis (described next),
osteoarthritis affects mainly the articular cartilage, although
the synovial membrane ofren becomes inflamed late in the
disease. Two major distinctions between osteoarthritis
and rheumatoid arthritis are that osteoarthritis first afflicts o
tl1e larger joints (knees, hips) and is due to_ wear and tear,
whereas rheumatoid arthritis first strikes smaller joints and
is an active attack of the cartilage. Osteoarthritis is the most
common reason for hip- and knee-replacement surgery.

lili Rheumatoid Arthritis
Rheumatoid arthritis (RA) is an autoimmune disease
in which the immune system of the body attacks its own
tissues-in this case, its own cartilage and jo~t linings.

Gamma ray photograph of swollen joints (bright spots) due to RA

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u

34. 5 Joints

Photograph of an individual with severe RA

RA is characterized by inflammation of the joint, which
causes swelling, pain, and loss of function. Usually, this
form of arthritis occurs bilaterally: If one wrist is affected,
the other is also likely to be affected, although often not
to the same degree.

The primary symptom of RA is inflammation of the
synovial membrane. If untreated, the membrane thickens,
and synovial fluid accumulates. The resulting pressure
causes pain and tenderness. The membrane then pro­
duces an abnormal granulation tissue, called pannus, that
adheres to the surface of the articular cartilage and some­
times erodes the cartilage completely. When the cartilage
is destroyed, fibrous tissue joins the exposed bone ends.
The fibrous tissue ossifies and fuses the joint so that it
becomes immovable-the ultimate crippling effect of RA.
The growth of the granulation tissue causes the distortion
of the fingers that characterizes hands of RA sufferers. II

Additional Clinical Considerations
• Dislocated Mandible
A dislocation (dis’-16-KA-shun; dis-= apart) or luxation
(luks-A-shun; luxatio = dislocation) is the displacement
of a bone from a joint with tearing of ligaments, tendons,
and articular capsules. It is usually caused by a blow or
fall, although unusual physical effort may be a factor.
For example, if the condylar processes of the mandible
pass anterior to the articular tubercles when you yawn or
take a large bite, a dislocated mandible (anterior displace­
ment) may occur. When the mandible is displaced in this
manner, the mouth remains wide open and the person is
unable to dciseTCTliis may be corrected by pressing the
thumbs downv.ca:rd on the lower molar teeth and pushing
the mandible backward. Other causes of a dislocated man­
dible include a lateral blow to the chin when the mouth is
open and a-fracture of the mandible.

1111 Knee Injuries
The knee joint is the joint most vulnerable to damage
because it is a mobile, weight-bearing joint and its stabil­
ity depends almost entirely on its associated ligaments
and muscles. Further, there is no correspondence of the
articulating bones. A swollen knee may occur immedi­
ately or hours after an injury. The initial swelling is due
to escape of blood from damaged blood vessels adjacent to
areas involving rupture of the anterior cruciate ligament,
damage to synovial membranes, torn menisci, fractures,
or collateral ligament sprains. Delayed swelling is due to
excessive production of synovial fluid, a condition com­
monly referred to as “water on the knee.’1 A common
type of knee injury in football is rupture of the tibial
collateral ligaments, often associated with tearing of the
anterior cruciate ligament and medial meniscus (torn car­
tilage). Usually, a hard blow to the lateral side of the knee
while the foot is fixed on the ground causes the damage.
A dislocated knee refers to the displacement of the tibia
relative to the femur. The most common type is disloca­
tion anteriorly, resulting from hyperextension of the knee.
A frequent consequence of a dislocated knee is damage to
the popliteal artery.

Iii Rotator Cuff Injury and Dislocated
and Separated Shoulder

Rotator cuff injury is a strain or tear in the rotator cuff
muscles and is a common injury among ·baseball pitchers,
volleyball players, racket sports players, swimmers, and
violinists, due to shoulder movements that involve vigor­
ous circumduction. It also occurs as a result of wear and
tear, aging, trauma, poor posture, improper lifting, and
repetitive motions in certain jobs, such as placing items
on a shelf above your head. Most often, there is tearing
of the supraspinatus muscle tendon of the rotator cuff.
This tendon is especially predisposed to wear-and-tear
because of its location between the head of the humerus
and acromion of the scapula, which compresses the tendon
during shoulder movements. Poor posture and poor body
mechanics also increase compression of the supraspinatus
muscle tendon.

The joint most commonly dislocated in adults is the
shoulder joint because its socket is quite shallow and the
bones are held together by supporting muscles. Usually in
a dislocated shoulder, the head of the humerus becomes
displaced inferiorly, where the articular capsl)le is least
protected. Dislocations of the mandible, elbow, fingers,
knee, or hip are less common.

A separated shoulder refers to an injury of the acro­
mioclavicular joint, a joint formed by the acromion of the
scapula and the acromial end of the clavicle. This condi­
tion is usually the result of forceful trauma to the joint, as
wherr.:lre· shoulder strikes the ground in a fall.

• Sprain and Strain
A sprain is the forcible wrenching or twisting of a joint that
stretches or tears its ligaments but does not dislocate the

bones. It occurs when the ligaments are stressed beyond
their normal capacity. Sprains also may damage surrounding
blood vessels, muscles, tendons, or nerves. Severe sprains
may be so painful that the joint cannot be moved. There is
considerable swelling, which results from chemicals released
by the damaged cells and hemorrhage of ruptured blood ves­
sels. The lateral ankle joint is most often sprained; the lower
back \s.,~norher frequent location. A strain is a stretched or
partialiji torn muscle or muscle and tendon. It often occurs
when a muscle contracts suddenly and powerfully-such
as the leg muscles of sprinters when they spring from the
blocks.

!lll Tennis Elbow, Little-League Elbow,
and Dislocation of the Radial Head

Tennis elbow most commonly refers to pain at or near
the lateral epicondyle of the humerus, usually caused by
an improperly executed backhand. The extensor muscles
strain or sprain, resulting in pain. Little-league elbow
typically develops as a result of a heavy pitching schedule
and/or a schedule that involves throwing curve balls, espe­
cially among youngsters. In this disorder, the elbow may
enlarge, fragment, or separate.

A dislocation of the radial head (nursemaid’s elbow)
is the most common upper limb dislocation in children. In
this injury, the head of the radius slides past or ruptures
the radial annular ligament, a ligament that forms a collar
around the head of the radius at the proximal radioulnar

Medical Terminology 35

joint. Dislocation is most apt to occur when a strong pull
is applied to the forearm while it is extended and supi-
nated, for instance while swinging a child around with o
outstretched arms. . !Im _.,/

Medical Terminology

Arthralgia (ar-THRAL-je-a; arthr- = joint; -algia = pain)
Pain in a joint.

Arthritis is a form of rheumatism in which the joints are
swollen, stiff, and painful. It afflicts about 45 million
people in the United States, and is the leading cause of
physical disability among adults over age 65.

Bursectomy (bur~SEK-t6-me; -ectomy = removal of)
Removal of a bursa.

Chondritis (kon-DRI-tis; chondr- = cartilage) Inflammation
of cartilage.

Rheumatism (ROO-ma-tizm) is any painful disorder of
the supporting structures of the body-bones, ligaments,
tendons, or muscles-that is not caused by infection or
injury.

Subluxation (sub-luks-A.-shun) A partial or incomplete
dislocation.

Synovitis (sin’-6-VI-tis) Inflanunation of a synovial mem­
brane in a joint.

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