8

why this

Joints matters

In this chapter, you will learn that

Joints determine how bones move relative to each other

by first asking then asking

8.1 How are joints classified? 8.6 What happens

when things go wrong?
then exploring
and finally, exploring

Developmental Aspects
8.2 Fibrous joints 8.3 Cartilaginous 8.4 Synovial joints of Joints
joints

looking closer at focusing on

Movement of 8.5 Selected

synovial joints synovial joints

T
he graceful movements of ballet dancers and the rough- focuses on the material binding the bones together and
and-tumble grapplings of football players demonstrate whether or not a joint cavity is present. Structurally, there
the great variety of motion allowed by joints, or ar- are fibrous, cartilaginous, and synovial joints (Table 8.1 on
ticulations—the sites where two or more bones meet. Our p. 275). Only synovial joints have a joint cavity.
joints have two fundamental functions: They The functional classification is based on the amount of
give our skeleton mobility, and they hold it to- movement allowed at the joint. On this basis, there are synar-
gether, sometimes playing a protective role in throses (sin″ar-thro′sēz; syn = together, arthro = joint), which
the process. are immovable joints; amphiarthroses (am″fe-ar-thro′sēz;
Joints are the weakest parts of the skeleton. amphi = on both sides), slightly movable joints; and diarthroses
Nonetheless, their structure resists various forces, (di″ar-thro′sēz; dia = through, apart), or freely movable joints.
such as crushing or tearing, that threaten to force Freely movable joints predominate in the limbs. Immovable and
them out of alignment. slightly movable joints are largely restricted to the axial skeleton.
This localization of functional joint types makes sense because
the less movable the joint, the more stable it is likely to be.
8.1 Joints are classified In general, fibrous joints are immovable, and synovial joints
are freely movable. However, cartilaginous joints have both
into three structural and three rigid and slightly movable examples. Since the structural cat-
functional categories egories are more clear-cut, we will use the structural classifica-
tion in this discussion, indicating functional properties where
Learning Objectives appropriate.
Define joint or articulation.
Classify joints by structure and by Check Your Understanding
function.
1. What functional joint class contains the least-mobile joints?
Joints are classified by struc- 2. How are joint mobility and stability related?
ture and by function. The
For answers, see Answers Appendix.
structural classification

< A physiotherapist works on a hip joint.

271

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 272 Unit 2 Covering, Support, and Movement of the Body

(a) Suture (b) Syndesmosis (c) Gomphosis

Joint held together with very short, Joint held together by a ligament. “Peg in socket” fibrous joint. Periodontal
interconnecting fibers, and bone edges Fibrous tissue can vary in length, but ligament holds tooth in socket.
interlock. Found only in the skull. is longer than in sutures.

Socket of
Suture Fibula alveolar
line process
Tibia

Root of
tooth

Fibrous
connective Ligament Periodontal
tissue ligament

Figure 8.1 Fibrous joints.

Syndesmoses
In fibrous joints, the bones are
8.2
In syndesmoses (sin″des-mo′sēz), the bones are connected
connected by fibrous tissue exclusively by ligaments (syndesmos = ligament), cords or
Learning Objective bands of fibrous tissue. The amount of movement allowed at
Describe the general structure of fibrous joints. Name and a syndesmosis depends on the length of the connecting fibers.
give an example of each of the three common types of Although the connecting fibers are always longer than those
fibrous joints. in sutures, they vary quite a bit in length. If the fibers are short
In fibrous joints, the bones are joined by the collagen fibers (as in the ligament connecting the distal ends of the tibia and
of connective tissue. No joint cavity is present. The amount of fibula, Figure 8.1b), little or no movement is allowed, a char-
movement allowed depends on the length of the connective acteristic best described as “give.” If the fibers are long (as in
tissue fibers. Most fibrous joints are immovable, although a the ligament-like interosseous membrane connecting the radius
few are slightly movable. The three types of fibrous joints are and ulna, Figure 7.29, p. 252), a large amount of movement is
sutures, syndesmoses, and gomphoses. possible.

Sutures Gomphoses
Sutures, literally “seams,” occur only between bones of the skull A gomphosis (gom-fo′sis) is a peg-in-socket fibrous joint
(Figure 8.1a). The wavy articulating bone edges interlock, and (Figure 8.1c). The only example is the articulation of a tooth
the junction is completely filled by a minimal amount of very with its bony alveolar socket. The term gomphosis comes from
short connective tissue fibers that are continuous with the peri- the Greek gompho, meaning “nail” or “bolt,” and refers to the
osteum. The result is nearly rigid splices that knit the bones way teeth are embedded in their sockets (as if hammered in).
together, yet allow the skull to expand as the brain grows dur- The fibrous connection in this case is the short periodontal
ing youth. During middle age, the fibrous tissue ossifies and ligament (Figure 23.12, p. 888).
the skull bones fuse into a single unit. At this stage, the closed Check Your Understanding
sutures are more precisely called synostoses (sin″os-to′sēz), lit-
erally, “bony junctions.” Because movement of the cranial bones 3. To what functional class do most fibrous joints belong?
would damage the brain, the immovable nature of sutures is a For answers, see Answers Appendix.
protective adaptation.

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 Chapter 8 Joints 273

(a) Synchondroses

Bones united by hyaline cartilage

Sternum (manubrium)

Epiphyseal
plate (temporary Joint between first rib
hyaline cartilage and sternum (immovable)
joint)

(b) Symphyses

Bones united by fibrocartilage

8

Body of vertebra

Fibrocartilaginous
intervertebral disc
(sandwiched between
Pubic symphysis
hyaline cartilage)

Figure 8.2 Cartilaginous joints.

synostoses. Another example of a synchondrosis is the immov-

8.3In cartilaginous joints, the able joint between the costal cartilage of the first rib and the
bones are connected by cartilage manubrium of the sternum (Figure 8.2a).

Learning Objective
Describe the general structure of cartilaginous joints.
Symphyses
Name and give an example of each of the two common A joint where fibrocartilage unites the bones is a symphysis
types of cartilaginous joints. (sim′fih-sis; “growing together”). Since fibrocartilage is compress-
In cartilaginous joints (kar″tĭ-laj′ĭ-nus), the articulating bones ible and resilient, it acts as a shock absorber and permits a limited
are united by cartilage. Like fibrous joints, they lack a joint cav- amount of movement at the joint. Even though fibrocartilage is
ity and are not highly movable. The two types of cartilaginous the main element of a symphysis, hyaline cartilage is also present
joints are synchondroses and symphyses. in the form of articular cartilages on the bony surfaces. Symphy-
ses are amphiarthrotic joints designed for strength with flexibility.
Examples include the intervertebral joints and the pubic symphy-
Synchondroses sis of the pelvis (Figure 8.2b, and see Table 8.2 on pp. 276–277).
A bar or plate of hyaline cartilage unites the bones at a syn-
chondrosis (sin″kon-dro′sis; “junction of cartilage”). Virtually Check Your Understanding
all synchondroses are synarthrotic (immovable). 4. MAKING connections Evan is 25 years old. Would you expect to
The most common examples of synchondroses are the find synchondroses at the ends of his femur? Explain. (Hint: See
epiphyseal plates in long bones of children (Figure 8.2a). Chapter 6.)
Epiphyseal plates are temporary joints and eventually become For answers, see Answers Appendix.

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 274 Unit 2 Covering, Support, and Movement of the Body

8.4 Synovial joints have a

fluid-filled joint cavity
Learning Objectives
Describe the structural characteristics of synovial joints.
Compare the structures and functions of bursae and
tendon sheaths.
List three natural factors that stabilize synovial joints.
Ligament
Name and describe (or perform) the common body
movements.
Name and provide examples of the six types of synovial Joint cavity
(contains
joints based on the movement(s) allowed. synovial fluid)
Synovial joints (si-no′ve-al; “joint eggs”) are those in which
the articulating bones are separated by a fluid-containing joint Articular (hyaline)
cavity. This arrangement permits substantial freedom of move- cartilage
ment, and all synovial joints are freely movable diarthroses. Fibrous
Nearly all joints of the limbs—indeed, most joints of the body— layer
8 fall into this class.
Synovial
Articular
membrane
capsule
General Structure (secretes
synovial
Synovial joints have six distinguishing features (Figure 8.3): fluid)

● Articular cartilage. Glassy-smooth hyaline cartilage covers the Periosteum

opposing bone surfaces as articular cartilage. These thin (1 mm
or less) but spongy cushions absorb compression placed on the
joint and thereby keep the bone ends from being crushed.
● Joint (articular) cavity. A feature unique to synovial joints, Figure 8.3 General structure of a synovial joint.
the joint cavity is really just a potential space that contains a
small amount of synovial fluid.
● Articular capsule. The joint cavity is enclosed by a two-lay-
the joint is loaded (put under pressure). This process, called
ered articular capsule, or joint capsule. The tough external weeping lubrication, lubricates the free surfaces of the carti-
fibrous layer is composed of dense irregular connective lages and nourishes their cells. (Remember, cartilage is avas-
tissue that is continuous with the periostea of the articulat- cular.) Synovial fluid also contains phagocytic cells that rid
ing bones. It strengthens the joint so that the bones are not the joint cavity of microbes and cellular debris.
pulled apart. The inner layer of the joint capsule is a synovial ● Reinforcing ligaments. Synovial joints are reinforced and
membrane composed of loose connective tissue. Besides lin- strengthened by a number of bandlike ligaments. Most often,
ing the fibrous layer internally, it covers all internal joint sur- these are capsular ligaments, which are thickened parts of
faces that are not hyaline cartilage. The synovial membrane’s the fibrous layer. In other cases, they remain distinct and are
function is to make synovial fluid. found outside the capsule (as extracapsular ligaments) or
deep to it (as intracapsular ligaments). Since intracapsular
● Synovial fluid. A small amount of slippery synovial fluid
ligaments are covered with synovial membrane, they do not
occupies all free spaces within the joint capsule. This fluid
actually lie within the joint cavity.
is derived largely by filtration from blood flowing through
People said to be double-jointed amaze the rest of us by
the capillaries in the synovial membrane. Synovial fluid has
placing both heels behind their neck. However, they have the
a viscous, egg-white consistency (ovum = egg) due to hyalu-
normal number of joints. It’s just that their joint capsules and
ronic acid secreted by cells in the synovial membrane, but it
ligaments are more stretchy and loose than average.
thins and becomes less viscous during joint activity.
Synovial fluid, which is also found within the articu- ● Nerves and blood vessels. Synovial joints are richly supplied
lar cartilages, provides a slippery, weight-bearing film that with sensory nerve fibers that innervate the capsule. Some of
reduces friction between the cartilages. Without this lubri- these fibers detect pain, as anyone who has suffered joint injury
cant, rubbing would wear away joint surfaces and excessive is aware, but most monitor joint position and stretch. Moni-
friction could overheat and destroy the joint tissues. The toring joint stretch is one of several ways the nervous system
synovial fluid is forced from the cartilages when a joint is senses our posture and body movements (see p. 509). Synovial
compressed; then as pressure on the joint is relieved, syno- joints are also richly supplied with blood vessels, most of which
vial fluid seeps back into the articular cartilages like water supply the synovial membrane. There, extensive capillary beds
into a sponge, ready to be squeezed out again the next time produce the blood filtrate that is the basis of synovial fluid.

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 Chapter 8 Joints 275

Table 8.1 Summary of Joint Classes

Structural Class Structural Characteristics Types Mobility

Fibrous Adjoining bones united by collagen fibers Suture (short fibers) Immobile (synarthrosis)

Syndesmosis (longer fibers) Slightly movable

(amphiarthrosis) and immobile

Gomphosis (periodontal ligament) Immobile

Cartilaginous Adjoining bones united by cartilage Synchondrosis (hyaline cartilage) Immobile

Symphysis (fibrocartilage) Slightly movable

Synovial Adjoining bones covered with articular • Plane • Condylar Freely movable (diarthrosis;
cartilage, separated by a joint cavity, and movements depend on design
• Hinge • Saddle
enclosed within an articular capsule lined of joint)
with synovial membrane • Pivot    • Ball-and-socket

Besides the basic components just described, certain syno- Bursae and Tendon Sheaths 8
vial joints have other structural features. Some, such as the hip
and knee joints, have cushioning fatty pads between the fibrous Bursae and tendon sheaths are not strictly part of synovial joints,
layer and the synovial membrane or bone. Others have discs or but they are often found closely associated with them (Figure 8.4).
wedges of fibrocartilage separating the articular surfaces. Where Essentially bags of lubricant, they act as “ball bearings” to reduce
present, these articular discs, or menisci (mĕ-nis′ki; “cres- friction between adjacent structures during joint activity. Bursae
cents”), extend inward from the articular capsule and partially or (ber′se; “purse”) are flattened fibrous sacs lined with synovial
completely divide the synovial cavity in two (see the menisci of membrane and containing a thin film of synovial fluid. They occur
the knee in Figure 8.7a, b, e, and f). Articular discs improve the where ligaments, muscles, skin, tendons, or bones rub together.
fit between articulating bone ends, making the joint more sta- A tendon sheath is essentially an elongated bursa that wraps
ble and minimizing wear and tear on the joint surfaces. Besides completely around a tendon subjected to friction, like a bun
the knees, articular discs occur in the jaw and a few other joints around a hot dog. They are common where several tendons are
(see notations in the Structural Type column in Table 8.2). crowded together within narrow canals (in the wrist, for example).

Acromion
of scapula
Subacromial Joint cavity
bursa containing
synovial fluid Bursa rolls
Fibrous layer of and lessens
articular capsule friction.

Articular
cartilage
Tendon
sheath

Synovial
membrane Humerus head Humerus moving
Tendon of rolls medially as
Fibrous arm abducts.
long head layer
of biceps
brachii muscle Humerus
(b) Enlargement of (a), showing how a bursa eliminates friction
where a ligament (or other structure) would rub against a bone

(a) Frontal section through the right shoulder joint

Figure 8.4 Bursae and tendon sheaths.

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 Table 8.2 Structural and Functional Characteristics of Body Joints
Illustration   J oint Articulating Bones Structural Type* Functional Type; Movements Allowed

Skull Cranial and facial Fibrous; suture Synarthrotic; no movement

bones
Temporo- Temporal bone of Synovial; modified Diarthrotic; gliding and uniaxial rotation;
mandibular skull and mandible hinge† (contains slight lateral movement, elevation,
articular disc) depression, protraction, and retraction of
mandible

Atlanto-occipital Occipital bone of skull Synovial; condylar Diarthrotic; biaxial; flexion, extension, lateral
and atlas flexion, circumduction of head on neck

Atlantoaxial Atlas (C1) and Synovial; pivot Diarthrotic; uniaxial; rotation of the head
axis (C2)

Intervertebral Between adjacent Cartilaginous; Amphiarthrotic; slight movement

vertebral bodies symphysis

Intervertebral Between articular Synovial; plane Diarthrotic; gliding

processes

Costovertebral Vertebrae (transverse Synovial; plane Diarthrotic; gliding of ribs

processes or bodies)
and ribs
8
Sternoclavicular Sternum and clavicle Synovial; shallow Diarthrotic; multiaxial (allows clavicle to
saddle (contains move in all axes)
articular disc)

Sternocostal Sternum and rib I Cartilaginous; Synarthrotic; no movement

(first) synchondrosis

Sternocostal Sternum and ribs II–VII Synovial; double plane Diarthrotic; gliding

Acromio- Acromion of scapula Synovial; plane Diarthrotic; gliding and rotation of scapula
clavicular and clavicle (contains articular disc) on clavicle

Shoulder Scapula and humerus Synovial; ball-and- Diarthrotic; multiaxial; flexion, extension,
(glenohumeral) socket abduction, adduction, circumduction,
rotation of humerus

Elbow Ulna (and radius) with Synovial; hinge Diarthrotic; uniaxial; flexion, extension of
humerus forearm

Proximal Radius and ulna Synovial; pivot Diarthrotic; uniaxial; pivot (convex head of
radioulnar radius rotates in radial notch of ulna)

Distal Radius and ulna Synovial; pivot Diarthrotic; uniaxial; rotation of radius
radioulnar (contains articular disc) around long axis of forearm to allow
pronation and supination

Wrist Radius and proximal Synovial; condylar Diarthrotic; biaxial; flexion, extension,
carpals abduction, adduction, circumduction of hand

Intercarpal Adjacent carpals Synovial; plane Diarthrotic; gliding

Carpometacarpal Carpal (trapezium) Synovial; saddle Diarthrotic; biaxial; flexion, extension,

of digit I and metacarpal I abduction, adduction, circumduction,
(thumb) opposition of metacarpal I

Carpometacarpal Carpal(s) and Synovial; plane Diarthrotic; gliding of metacarpals

of digits II–V metacarpal(s)

Metacarpo- Metacarpal and Synovial; condylar Diarthrotic; biaxial; flexion, extension,

phalangeal proximal phalanx abduction, adduction, circumduction of
(knuckle) fingers

Interphalangeal Adjacent phalanges Synovial; hinge Diarthrotic; uniaxial; flexion, extension of

(finger) fingers

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 Chapter 8 Joints 277

Table 8.2 (continued)­

Illustration   J oint Articulating Bones Structural Type* Functional Type; Movements Allowed

Sacroiliac Sacrum and coxal Synovial; plane in Diarthrotic in child; amphiarthrotic in adult;
bone childhood, increasingly (more movement during pregnancy)
fibrous in adult

Pubic symphysis Pubic bones Cartilaginous; Amphiarthrotic; slight movement (enhanced

symphysis during pregnancy)

Hip (coxal) Hip bone and femur Synovial; ball-and- Diarthrotic; multiaxial; flexion, extension,
socket abduction, adduction, rotation,
circumduction of thigh

Knee Femur and tibia Synovial; modified Diarthrotic; biaxial; flexion, extension of leg,
(tibiofemoral) hinge† (contains some rotation allowed in flexed position
articular discs)

Knee Femur and patella Synovial; plane Diarthrotic; gliding of patella

(femoropatellar)

Superior Tibia and fibula Synovial; plane Diarthrotic; gliding of fibula 8

tibiofibular (proximally)

Inferior Tibia and fibula Fibrous; syndesmosis Synarthrotic; slight “give” during dorsiflexion
tibiofibular (distally)

Ankle Tibia and fibula with Synovial; hinge Diarthrotic; uniaxial; dorsiflexion, and plantar
talus flexion of foot

Intertarsal Adjacent tarsals Synovial; plane Diarthrotic; gliding; inversion and eversion
of foot
Tarsometatarsal Tarsal(s) and Synovial; plane Diarthrotic; gliding of metatarsals
metatarsal(s)
Metatarso- Metatarsal and Synovial; condylar Diarthrotic; biaxial; flexion, extension,
phalangeal proximal phalanx abduction, adduction, circumduction of
great toe

Interpha- Adjacent phalanges Synovial; hinge Diarthrotic; uniaxial; flexion, extension of

langeal (toe) toes

*Fibrous joints indicated by orange circles (•); cartilaginous joints by blue circles (•); synovial joints by purple circles (•).
†
  These modified hinge joints are structurally bicondylar.

Factors Influencing the Stability Ligaments

of Synovial Joints The capsules and ligaments of synovial joints unite the bones
and prevent excessive or undesirable motion. As a rule, the
Because joints are constantly stretched and compressed, they more ligaments a joint has, the stronger it is. However, when
must be stabilized so that they do not dislocate (come out of other stabilizing factors are inadequate, undue tension is placed
alignment). The stability of a synovial joint depends chiefly on on the ligaments and they stretch. Stretched ligaments stay
three factors: the shapes of the articular surfaces; the number stretched, like taffy, and a ligament can stretch only about 6%
and positioning of ligaments; and muscle tone. of its length before it snaps. Thus, when ligaments are the major
means of bracing a joint, the joint is not very stable.
Articular Surfaces
The shapes of articular surfaces determine what movements are Muscle Tone
possible at a joint, but surprisingly, articular surfaces play only For most joints, the muscle tendons that cross the joint are
a minor role in joint stability. Many joints have shallow sock- the most important stabilizing factor. These tendons are kept
ets or noncomplementary articulating surfaces (“misfits”) that under tension by the tone of their muscles. (Muscle tone is
actually hinder joint stability. But when articular surfaces are defined as low levels of contractile activity in relaxed muscles
large and fit snugly together, or when the socket is deep, stabil- that keep the muscles healthy and ready to react to stimula-
ity is vastly improved. The ball and deep socket of the hip joint tion.) Muscle tone is extremely important in reinforcing the
provide the best example of a joint made extremely stable by the shoulder and knee joints and the arches of the foot.
shape of its articular surfaces.

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 278 Unit 2 Covering, Support, and Movement of the Body

Movements Allowed by Synovial Joints

Every skeletal muscle of the body is attached to bone or other
connective tissue structures at no fewer than two points. The
muscle’s origin is attached to the immovable (or less movable)
bone. Its other end, the insertion, is attached to the movable bone.
Body movement occurs when muscles contract across joints and
their insertion moves toward their origin. The movements can
be described in directional terms relative to the lines, or axes,
around which the body part moves and the planes of space along
which the movement occurs, that is, along the transverse, frontal,
or sagittal plane. (See Chapter 1 to review these planes.) Gliding
Range of motion allowed by synovial joints varies from
nonaxial movement (slipping movements only) to uniaxial
movement (movement in one plane) to biaxial movement
(a) Gliding movements at the wrist
(movement in two planes) to multiaxial movement (move-
ment in or around all three planes of space and axes). Range of
motion varies greatly. In some people, such as trained gymnasts Extension
Hyperextension
or acrobats, range of joint movement may be extraordinary. The
8 ranges of motion at the major joints are given in the far right
column of Table 8.2.
There are three general types of movements: gliding, angular
movements, and rotation. The most common body movements Flexion
allowed by synovial joints are described next and illustrated in
Figure 8.5.

Gliding Movements
Gliding occurs when one flat, or nearly flat, bone surface
glides or slips over another (back-and-forth and side-to-side;
Figure 8.5a) without appreciable angulation or rotation. Glid-
ing occurs at the intercarpal and intertarsal joints, and between (b) Angular movements: flexion, extension, and hyperextension of
the flat articular processes of the vertebrae (Table 8.2). the neck

Angular Movements
Angular movements (Figure 8.5b–e) increase or decrease the Extension
angle between two bones. These movements may occur in any
plane of the body and include flexion, extension, hyperexten-
sion, abduction, adduction, and circumduction.
Flexion Flexion (flek′shun) is a bending movement, usually
along the sagittal plane, that decreases the angle of the joint and
brings the articulating bones closer together. Examples include
bending the head forward on the chest (Figure 8.5b) and bend- Hyperextension Flexion
ing the body trunk or the knee from a straight to an angled
position (Figure 8.5c and d). As a less obvious example, the arm
is flexed at the shoulder when the arm is lifted in an anterior
direction (Figure 8.5d).
Extension Extension is the reverse of flexion and occurs at the
same joints. It involves movement along the sagittal plane that
increases the angle between the articulating bones and typically
straightens a flexed limb or body part. Examples include straight-
ening a flexed neck, body trunk, elbow, or knee (Figure 8.5b–d).

(c) Angular movements: flexion, extension, and hyperextension of

Figure 8.5 Movements allowed by synovial joints. the vertebral column

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 Chapter 8 Joints 279

Flexion Hyper-
extension

Extension

Flexion

8
Extension

(d) Angular movements: flexion, extension, and hyperextension at the shoulder and knee

Continuing such movements beyond the anatomical position is

called hyperextension (Figure 8.5b–d).
Abduction Abduction (“moving away”) is movement of a
limb away from the midline or median plane of the body, along
the frontal plane. Raising the arm or thigh laterally is an exam-
ple of abduction (Figure 8.5e). For the fingers or toes, abduction
means spreading them apart. In this case the “midline” is the
third finger or second toe. Notice, however, that lateral bending
of the trunk away from the body midline in the frontal plane is Abduction
called lateral flexion, not abduction.
Adduction Adduction (“moving toward”) is the opposite of
abduction, so it is the movement of a limb toward the body
midline or, in the case of the digits, toward the midline of the
hand or foot (Figure 8.5e). Adduction
Circumduction

Circumduction Circumduction (Figure 8.5e) is moving a

limb so that it describes a cone in space (circum = around; duco
= to draw). The distal end of the limb moves in a circle, while
the point of the cone (the shoulder or hip joint) is more or less
stationary. A pitcher winding up to throw a ball is actually cir-
cumducting his or her pitching arm. Because circumduction
consists of flexion, abduction, extension, and adduction per-
formed in succession, it is the quickest way to exercise the many
muscles that move the hip and shoulder ball-and-socket joints.

Rotation (e) Angular movements: abduction, adduction, and

circumduction of the upper limb at the shoulder
Rotation is the turning of a bone around its own long axis. It
is the only movement allowed between the first two cervical
Figure 8.5 (continued)

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 280 Unit 2 Covering, Support, and Movement of the Body

surface approaches the shin is dorsiflexion (corresponds to

wrist extension), whereas depressing the foot (pointing the
toes) is plantar flexion (corresponds to wrist flexion).
Inversion and Eversion Inversion and eversion are special
Rotation movements of the foot (Figure 8.6c). In inversion, the sole of the
foot turns medially. In eversion, the sole faces laterally.
Protraction and Retraction Nonangular anterior and poste-
rior movements in a transverse plane are called protraction and
retraction, respectively (Figure 8.6d). The mandible is protracted
when you jut out your jaw and retracted when you bring it back.
Elevation and Depression Elevation means lifting a body
part superiorly (Figure 8.6e). For example, the scapulae are
Lateral elevated when you shrug your shoulders. Moving the elevated
rotation
part inferiorly is depression. During chewing, the mandible is
alternately elevated and depressed.
Medial
rotation Opposition The saddle joint between metacarpal I and the
trapezium allows a movement called opposition of the thumb
8
(Figure 8.6f). This movement is the action taken when you
touch your thumb to the tips of the other fingers on the same
hand. It is opposition that makes the human hand such a fine
tool for grasping and manipulating objects.

Types of Synovial Joints

(f) Rotation of the head, neck, and lower limb Although all synovial joints have structural features in com-
mon, they do not have a common structural plan. Based on
Figure 8.5 (continued) Movements allowed by synovial the shape of their articular surfaces, which in turn deter-
joints. mine the movements allowed, synovial joints can be clas-
sified further into six major categories—plane, hinge, pivot,
vertebrae and is common at the hip (Figure 8.5f) and shoulder condylar (or ellipsoid), saddle, and ball-and-socket joints. The
joints. Rotation may be directed toward the midline or away properties of these joints are summarized in Focus on Types of
from it. For example, in medial rotation of the thigh, the femur’s Synovial Joints (Focus Figure 8.1) on pp. 282–283.
anterior surface moves toward the median plane of the body;
lateral rotation is the opposite movement. Check Your Understanding
5. How do bursae and tendon sheaths improve joint function?
Special Movements 6. Generally speaking, what factor is most important in stabilizing
Certain movements do not fit into any of the above categories synovial joints?
and occur at only a few joints. Some of these special movements 7. John bent over to pick up a dime. What movement was
are illustrated in Figure 8.6. occurring at his hip joint, at his knees, and between his index
finger and thumb?
Supination and Pronation The terms supination (soo″pĭ- 8. On the basis of movement allowed, which of the following
na′shun; “turning backward”) and pronation (pro-na′shun; joints are uniaxial? Hinge, condylar, saddle, pivot.
“turning forward”) refer to the movements of the radius around For answers, see Answers Appendix.
the ulna (Figure 8.6a). Rotating the forearm laterally so that the
palm faces anteriorly or superiorly is supination. In the anatomical
position, the hand is supinated and the radius and ulna are parallel. 8.5 Five examples illustrate the
In pronation, the forearm rotates medially and the palm
faces posteriorly or inferiorly. Pronation moves the distal end of diversity of synovial joints
the radius across the ulna so that the two bones form an X. This Learning Objective
is the forearm’s position when we are standing in a relaxed man-
Describe the knee, shoulder, elbow, hip, and jaw joints in
ner. Pronation is a much weaker movement than supination. terms of articulating bones, anatomical characteristics of
A trick to help you keep these terms straight: A pro basketball the joint, movements allowed, and joint stability.
player pronates his or her forearm to dribble the ball.
In this section, we examine five joints in detail: knee, shoulder,
Dorsiflexion and Plantar Flexion of the Foot The up-and- elbow, hip, and temporomandibular (jaw) joints. All have the six
down movements of the foot at the ankle are given more spe- distinguishing characteristics of synovial joints, and we will not
cific names (Figure 8.6b). Lifting the foot so that its superior
(Text continues on p. 284.)­

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 Chapter 8 Joints 281

Dorsiflexion

Pronation Supination
(radius rotates (radius and ulna
over ulna) are parallel)

Plantar flexion
P

8
(a) Pronation (P) and supination (S) (b) Dorsiflexion and plantar flexion

Inversion Eversion
Protraction
of mandible Retraction
of mandible

(c) Inversion and eversion (d) Protraction and retraction

Opposition

Elevation Depression
of mandible of mandible

(e) Elevation and depression (f) Opposition

Figure 8.6 Special body movements.

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 FOCUS Synovial Joints
Focus Figure 8.1 Six types of synovial joint shapes determine
the movements that can occur at a joint.

(a) Plane joint Nonaxial movement

Metacarpals Flat
articular
surfaces
Gliding
Carpals

Examples: Intercarpal joints, intertarsal joints, joints between vertebral articular surfaces

(b) Hinge joint Uniaxial movement

Humerus
Medial/lateral
axis
Cylinder
Trough

Ulna Flexion and extension

Examples: Elbow joints, interphalangeal joints

(c) Pivot joint Uniaxial movement

Vertical axis

Sleeve
(bone and
ligament)

Ulna Axle (rounded

bone)

Rotation
Radius

Examples: Proximal radioulnar joints, atlantoaxial joint

282

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 (d) Condylar joint Biaxial movement

Medial/ Anterior/
Phalanges lateral posterior
axis axis

Oval
articular
Metacarpals surfaces

Flexion and extension Adduction and abduction

Examples: Metacarpophalangeal (knuckle) joints, wrist joints

(e) Saddle joint Biaxial movement

Medial/ Anterior/
lateral posterior
axis axis

Articular
Metacarpal Ι surfaces
are both
concave
and convex Adduction and abduction Flexion and extension

Trapezium
Example: Carpometacarpal joints of the thumbs

(f) Ball-and-socket joint Multiaxial movement

Cup Medial/lateral Anterior/posterior Vertical axis
(socket) axis axis

Scapula

Spherical
head
(ball)
Humerus
Flexion and extension Adduction and
abduction Rotation

Examples: Shoulder joints and hip joints

283

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 284 Unit 2 Covering, Support, and Movement of the Body

Tendon of
quadriceps
femoris Anterior

Suprapatellar Anterior
Femur bursa cruciate
Articular ligament
Patella Articular
capsule cartilage on
Articular
Posterior Subcutaneous lateral tibial
cartilage
cruciate prepatellar bursa condyle
on medial
ligament Synovial cavity tibial
Lateral condyle
meniscus Lateral meniscus
Infrapatellar
Anterior
fat pad
cruciate
ligament Deep infrapatellar Medial Lateral
bursa meniscus meniscus
Tibia
Patellar ligament Posterior
cruciate
ligament

(a) Sagittal section through the right knee joint (b) Superior view of the right tibia in the knee joint, showing
the menisci and cruciate ligaments
8

Tendon of Femur
adductor
magnus Articular
Quadriceps capsule
femoris Medial head of
muscle gastrocnemius Oblique
muscle popliteal
Tendon of ligament
quadriceps Lateral
femoris head of
muscle gastrocnemius
Popliteus muscle
muscle
Patella (cut) Bursa
Medial
Lateral patellar Fibular
Tibial
patellar retinaculum collateral
collateral
retinaculum ligament
Tibial ligament
Fibular collateral Arcuate
collateral ligament popliteal
ligament Tendon of ligament
Patellar semimembranosus
ligament muscle
Fibula Tibia
Tibia

(c) Anterior view of right knee (d) Posterior view of the joint capsule, including ligaments

Figure 8.7 The knee joint. Explore human cadaver

>Study Area>

discuss these common features again. Instead, we will empha- between the femoral condyles above and the C-shaped menisci, or
size the unique structural features, functional abilities, and, in semilunar cartilages, of the tibia below (Figure 8.7b and e). Besides
certain cases, functional weaknesses of each of these joints. deepening the shallow tibial articular surfaces, the menisci help
prevent side-to-side rocking of the femur on the tibia and absorb
Knee Joint shock transmitted to the knee joint. However, the menisci are
attached only at their outer margins and are frequently torn free.
The knee joint is the largest and most complex joint in the body The tibiofemoral joint acts primarily as a hinge, permitting
(Figure 8.7). Despite its single joint cavity, the knee consists of flexion and extension. However, structurally it is a bicondylar
three joints in one: an intermediate one between the patella and joint. Some rotation is possible when the knee is partly flexed,
the lower end of the femur (the femoropatellar joint), and lateral and when the knee is extending. But, when the knee is fully
and medial joints (collectively known as the tibiofemoral joint)

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 Chapter 8 Joints 285
Posterior
cruciate
ligament
Fibular
collateral Medial
ligament condyle
Tibial
collateral
Lateral ligament Medial femoral condyle
condyle
of femur Anterior cruciate ligament
Anterior
cruciate
Lateral Medial meniscus on
ligament
meniscus medial tibial condyle
Medial
meniscus
Tibia

Patellar
ligament

Fibula Patella

Quadriceps
8
tendon Patella

(e) Anterior view of flexed knee, showing the cruciate ligaments (f) Photograph of an opened knee joint; view similar to (e)
(articular capsule removed, and quadriceps tendon cut
and reflected distally)

Figure 8.7 (continued)

extended, side-to-side movements and rotation are strongly medial epicondyle of the femur to the medial condyle of the tibial
resisted by ligaments and the menisci. The femoropatellar joint shaft below and is fused to the medial meniscus (Figure 8.7c–e).
is a plane joint, and the patella glides across the distal end of the ● The oblique popliteal ligament (pop″lĭ-te′al) is actually part
femur during knee flexion. of the tendon of the semimembranosus muscle that fuses
The knee joint is unique in that its joint cavity is only par- with the joint capsule and helps stabilize the posterior aspect
tially enclosed by a capsule. The relatively thin articular cap- of the knee joint (Figure 8.7d).
sule is present only on the sides and posterior aspects of the ● The arcuate popliteal ligament arcs superiorly from the
knee, where it covers the bulk of the femoral and tibial condyles.
head of the fibula over the popliteus muscle and reinforces
Anteriorly, where the capsule is absent, three broad ligaments
the joint capsule posteriorly (Figure 8.7d).
run from the patella to the tibia below. These are the patellar
ligament flanked by the medial and lateral patellar retinacula The knee’s intracapsular ligaments are called cruciate liga-
(ret″ĭ-nak′u-lah; “retainers”), which merge imperceptibly into ments (kroo′she-āt) because they cross each other, forming an
the articular capsule on each side (Figure 8.7c). The patellar X (cruci = cross) in the notch between the femoral condyles.
ligament and retinacula are actually continuations of the tendon They act as restraining straps to help prevent anterior-posterior
of the bulky quadriceps muscle of the anterior thigh. Physicians displacement of the articular surfaces and to secure the articu-
tap the patellar ligament to test the knee-jerk reflex. lating bones when we stand (Figure 8.7a, b, e). Although these
The synovial cavity of the knee joint has a complicated shape, ligaments are in the joint capsule, they are outside the syno-
with several extensions that lead into “blind alleys.” At least a dozen vial cavity, and synovial membrane nearly covers their surfaces.
bursae are associated with this joint, some of which are shown Note that the two cruciate ligaments both run superiorly to the
in Figure 8.7a. For example, notice the subcutaneous prepatellar femur and are named for their tibial attachment site.
bursa, which is often injured when the knee is bumped anteriorly. The anterior cruciate ligament attaches to the anterior
All three types of joint ligaments (extracapsular, capsular, intercondylar area of the tibia (Figure 8.7b, e). From there it
and intracapsular) stabilize and strengthen the capsule of the passes posteriorly, laterally, and upward to attach to the femur
knee joint. All of the capsular and extracapsular ligaments act on the medial side of its lateral condyle. This ligament prevents
to prevent hyperextension of the knee and are stretched tight forward sliding of the tibia on the femur and checks hyperex-
when the knee is extended. These include: tension of the knee. It is somewhat lax when the knee is flexed,
● The extracapsular fibular and tibial collateral ligaments are also and taut when the knee is extended.
critical in preventing lateral or medial rotation when the knee is The stronger posterior cruciate ligament is attached to the
extended. The broad, flat tibial collateral ligament runs from the posterior intercondylar area of the tibia and passes anteriorly,

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 286 Unit 2 Covering, Support, and Movement of the Body

When thinking of common knee injuries, remember the

3 Cs: collateral ligaments, cruciate ligaments, and cartilages
Lateral Medial
(menisci). Most dangerous are lateral blows to the extended
Patella knee. These forces tear the tibial collateral ligament and the
Hockey puck (outline) medial meniscus attached to it, as well as the anterior cruciate
ligament (ACL) (Figure 8.8). It is estimated that 50% of all
professional football players have serious knee injuries during
their careers.
Tibial Although less devastating than the injury just described, inju-
collateral
ligament ries that affect only the anterior cruciate ligament are becoming
(torn) more common, particularly as women’s sports become more
vigorous and competitive. Most ACL injuries occur when a run-
Medial
meniscus ner changes direction quickly, twisting a hyperextended knee. A
(torn) torn ACL heals poorly, so repair usually requires a graft taken
from either the patellar ligament, the hamstring tendon, or the
Anterior
cruciate calcaneal tendon. ✚
ligament
(torn)
Shoulder (Glenohumeral) Joint
8 In the shoulder joint, stability has been sacrificed to provide
the most freely moving joint of the body. The shoulder joint
Figure 8.8 The “unhappy triad:” ruptured ACL, ruptured is a ball-and-socket joint. The large hemispherical head of the
tibial collateral ligament, and torn meniscus. A common injury humerus fits in the small, shallow glenoid cavity of the scapula
in hockey, soccer, and American football.
(Figure 8.9), like a golf ball sitting on a tee. Although the gle-
noid cavity is slightly deepened by a rim of fibrocartilage, the
glenoid labrum (labrum = lip), it is only about one-third the
medially, and superiorly to attach to the femur on the lateral side
size of the humeral head and contributes little to joint stability
of the medial condyle (Figure 8.7a, b, e). This ligament prevents
(Figure 8.9d).
backward displacement of the tibia or forward sliding of the femur.
The articular capsule enclosing the joint cavity (from the
The knee capsule is heavily reinforced by muscle tendons.
margin of the glenoid cavity to the anatomical neck of the
Most important are the strong tendons of the quadriceps muscles
humerus) is remarkably thin and loose, qualities that contrib-
of the anterior thigh and the tendon of the semimembranosus
ute to this joint’s freedom of movement. The few ligaments
muscle posteriorly (Figure 8.7c and d). The greater the strength
reinforcing the shoulder joint are located primarily on its ante-
and tone of these muscles, the less the chance of knee injury.
rior aspect. The superiorly located coracohumeral ligament
The knees have a built-in locking device that provides steady
(kor′ah-ko-hu′mer-ul) provides the only strong thickening of
support for the body in the standing position. As we begin
the capsule and helps support the weight of the upper limb (Fig-
to stand up, the wheel-shaped femoral condyles roll like ball
ure 8.9c). Three glenohumeral ligaments (glĕ″no-hu′mer-ul)
bearings across the tibial condyles and the flexed leg begins
strengthen the front of the capsule somewhat but are weak and
to extend at the knee. Because the lateral femoral condyle
may even be absent (Figure 8.9c, d).
stops rolling before the medial condyle stops, the femur spins
Muscle tendons that cross the shoulder joint contribute most to
(rotates) medially on the tibia, until the cruciate and collateral
this joint’s stability. The “superstabilizer” is the tendon of the long
ligaments of the knee are twisted and taut and the menisci are
head of the biceps brachii muscle of the arm (Figure 8.9c). This
compressed. The tension in the ligaments effectively locks the
tendon attaches to the superior margin of the glenoid labrum,
joint into a rigid structure that cannot be flexed again until
travels through the joint cavity, and then runs within the intertu-
it is unlocked. This unlocking is accomplished by the popli-
bercular sulcus of the humerus. It secures the head of the humerus
teus muscle (see Figure 8.7d and Table 10.15, pp. 392–397). It
against the glenoid cavity.
rotates the femur laterally on the tibia, causing the ligaments to
Four other tendons (and the associated muscles) make up the
become untwisted and slack.
rotator cuff. This cuff encircles the shoulder joint and blends
with the articular capsule. The muscles include the subscapula-
Hom e o stati c ClinicAL ris, supraspinatus, infraspinatus, and teres minor. (The rotator
I m bal an ce 8. 1 cuff muscles are illustrated in Figure 10.15, pp. 373–374.) The
Of all body joints, the knees are most susceptible to sports injuries rotator cuff can be severely stretched when the arm is vigorously
because of their high reliance on nonarticular factors for stability circumducted; this is a common injury of baseball pitchers. As
and the fact that they carry the body’s weight. The knee can absorb noted in Chapter 7, shoulder dislocations are fairly common.
a vertical force equal to nearly seven times body weight. However, Because the shoulder’s reinforcements are weakest anteriorly
it is very vulnerable to horizontal blows, such as those that occur and inferiorly, the humerus tends to dislocate in the forward
during blocking and tackling in football and in ice hockey. and downward direction.

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 Chapter 8 Joints 287
Acromion
of scapula
Coracoacromial
ligament Synovial cavity
Subacromial of the glenoid
bursa cavity containing
synovial fluid
Fibrous layer of
articular capsule Articular
cartilage
Tendon
sheath
Synovial membrane
Fibrous layer of
Tendon of articular capsule
long head
of biceps
brachii muscle Humerus

(a) Frontal section through right shoulder joint (b) Cadaver photo corresponding to (a)
8
Acromion Acromion
Coracoid
Coracoacromial process
ligament Coracoid
process
Subacromial Articular
capsule Articular
bursa capsule
reinforced by
glenohumeral Glenoid cavity
Coracohumeral
ligaments
ligament Glenoid labrum

Transverse Subscapular Tendon of long

humeral bursa head of biceps
ligament brachii muscle
Tendon of the
subscapularis Glenohumeral
Tendon sheath ligaments
muscle
Tendon of the
Tendon of subscapularis
long head Scapula
muscle
of biceps
brachii Scapula
muscle Posterior Anterior
(c) Anterior view of right shoulder joint capsule (d) Lateral view of socket of right shoulder joint,
humerus removed

Acromion
(cut) Rotator cuff
muscles
Glenoid (cut)
cavity of
scapula

Glenoid
labrum

Capsule of
shoulder
joint
(opened)

Explore human cadaver

Head of
humerus >Study Area>

(e) Posterior view of an opened right shoulder joint Figure 8.9 The shoulder joint.

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 288 Unit 2 Covering, Support, and Movement of the Body

Articular
capsule
Synovial Humerus
membrane
Humerus Anular
Synovial cavity ligament
Articular cartilage Radius
Fat pad Lateral
Coronoid process
epicondyle
Tendon of Tendon of
triceps brachialis muscle Articular
muscle capsule
Ulna
Bursa Radial
collateral
Trochlea ligament
Articular cartilage Olecranon
of the trochlear
notch Ulna

(a) Median sagittal section through right elbow (lateral view) (b) Lateral view of right elbow joint

Articular
8 capsule
Humerus
Anular Humerus
Anular ligament
ligament
Medial Coronoid
epicondyle process
Medial
Radius epicondyle
Articular Ulnar
capsule collateral
ligament
Radius
Coronoid
process
of ulna Ulnar
Ulna
collateral
Ulna ligament

(c) Cadaver photo of medial view of right elbow (d) Medial view of right elbow

Figure 8.10 The elbow joint. Explore human cadaver

>Study Area>

Elbow Joint the radial collateral ligament, a triangular ligament on the lateral
side (Figure 8.10b, c, and d). Additionally, tendons of several
Our upper limbs are flexible extensions that permit us to reach out arm muscles, such as the biceps and triceps, cross the elbow
and manipulate things in our environment. Besides the shoulder joint and provide security.
joint, the most prominent of the upper limb joints is the elbow. The radius is a passive “onlooker” in the angular elbow
The elbow joint provides a stable and smoothly operating hinge movements. However, its head rotates within the anular liga-
that allows flexion and extension only (Figure 8.10). Within the ment during supination and pronation of the forearm.
joint, both the radius and ulna articulate with the condyles of
the humerus, but it is the close gripping of the trochlea by the
ulna’s trochlear notch that forms the “hinge” and stabilizes this Hip Joint
joint (Figure 8.10a). A relatively lax articular capsule extends The hip (coxal) joint, like the shoulder joint, is a ball-and-socket
inferiorly from the humerus to the ulna and radius, and to the joint. It has a good range of motion, but not nearly as wide as the
anular ligament (an′u-lar) surrounding the head of the radius shoulder’s range. Movements occur in all possible planes but are
(Figure 8.10b, c). limited by the joint’s strong ligaments and its deep socket.
Anteriorly and posteriorly, the articular capsule is thin and The hip joint is formed by the articulation of the spherical
allows substantial freedom for elbow flexion and extension. head of the femur with the deeply cupped acetabulum of the hip
However, side-to-side movements are restricted by two strong bone (Figure 8.11). The depth of the acetabulum is enhanced
capsular ligaments: the ulnar collateral ligament medially, and by a circular rim of fibrocartilage called the acetabular labrum

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 Chapter 8 Joints 289
Hip (coxal) bone Acetabular
Articular cartilage labrum
Ligament of the
head of the femur Synovial
Acetabular labrum
(ligamentum teres) membrane
Femur
Ligament
of the head
of the femur
(ligamentum
teres)

Head
of femur

Articular
capsule (cut)
Synovial cavity
Articular capsule

(a) Frontal section through the right hip joint (b) Photo of the interior of the hip joint, lateral view

Iliofemoral
ligament Anterior inferior Iliofemoral
iliac spine ligament
Ischium Ischiofemoral
ligament Pubofemoral
ligament

Greater
Greater
trochanter
trochanter
of femur

(c) Posterior view of right hip joint, capsule in place (d) Anterior view of right hip joint, capsule in place

Figure 8.11 The hip joint. Explore human cadaver

>Study Area>

(as″ĕ-tab′u-lar) (Figure 8.11a, b). The labrum’s diameter is less The ligament of the head of the femur, also called the liga-
than that of the head of the femur, and these articular surfaces mentum teres, is a flat intracapsular band that runs from the
fit snugly together, so hip joint dislocations are rare. femur head to the lower lip of the acetabulum (Figure 8.11a, b).
The thick articular capsule extends from the rim of the ace- This ligament is slack during most hip movements, so it is not
tabulum to the neck of the femur and completely encloses the important in stabilizing the joint. In fact, its mechanical func-
joint. Several strong ligaments reinforce the capsule of the hip tion (if any) is unclear, but it does contain an artery that helps
joint. These include the iliofemoral ligament (il″e-o-fem′o-ral), supply the head of the femur. Damage to this artery may lead to
a strong V-shaped ligament anteriorly; the pubofemoral liga- severe arthritis of the hip joint.
ment (pu″bo-fem′o-ral), a triangular thickening of the inferior Muscle tendons that cross the joint and the bulky hip and
part of the capsule; and the ischiofemoral ligament (is″ke-o- thigh muscles that surround it contribute to its stability and
fem′o-ral), a spiraling posterior ligament (Figure 8.11c, d). strength. In this joint, however, stability comes chiefly from
These ligaments are arranged in such a way that they “screw” the deep socket that securely encloses the femoral head and the
the femur head into the acetabulum when a person stands up strong capsular ligaments.
straight, thereby providing stability.

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 290 Unit 2 Covering, Support, and Movement of the Body

Articular disc
Mandibular fossa
Articular tubercle Articular
tubercle
Zygomatic process
Infratemporal fossa Mandibular
fossa Superior
joint
cavity
External
acoustic
meatus Articular
capsule

Lateral
ligament
Articular Synovial
capsule membranes

Ramus of
8 mandible
Condylar
process of
mandible

Ramus of Inferior joint

mandible cavity

(a) Location of the joint in the skull (b) Enlargement of a sagittal section through the joint

Superior view

Outline of the
mandibular
fossa

(c) Lateral excursion: lateral (side-to-side) movements of the mandible

Figure 8.12 The temporomandibular compartment of the joint cavity allows the forward to brace against the articular tubercle
(jaw) joint. In (b), note that the two condylar process of the mandible to rotate in when the mouth opens wide, and also allows
parts of the joint cavity allow different opening and closing the mouth. The superior lateral excursion of this joint (c).
movements, indicated by arrows. The inferior compartment lets the condylar process move

Temporomandibular Joint temporal bone has a more complex shape. Posteriorly, it forms
the concave mandibular fossa; anteriorly it forms a dense knob
The temporomandibular joint (TMJ), or jaw joint, is a modified called the articular tubercle. The lateral aspect of the loose artic-
hinge joint. It lies just anterior to the ear (Figure 8.12). At this joint, ular capsule that encloses the joint is thickened into a lateral liga-
the condylar process of the mandible articulates with the inferior ment. Within the capsule, an articular disc divides the synovial
surface of the squamous part of the temporal bone. The mandible’s cavity into superior and inferior compartments (Figure 8.12a, b).
condylar process is egg shaped, whereas the articular surface of the

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 Chapter 8 Joints 291
Two distinct kinds of movement occur at the TMJ. First, the Few of us pay attention to our joints unless something goes
concave inferior disc surface receives the condylar process of the wrong. Although remarkably strong, joints are more likely to
mandible and allows the familiar hingelike movement of depress- be injured by forces the bony skeleton can withstand. This is
ing and elevating the mandible while opening and closing the the price of our flexibility. Joint pain and malfunction can be
mouth (Figure 8.12a, b). Second, the superior disc surface glides caused by a number of factors besides traumatic injury, includ-
anteriorly along with the condylar process when the mouth is ing inflammatory conditions and degenerative processes due to
opened wide. This anterior movement braces the condylar process friction and wear.
against the articular tubercle, so that the mandible is not forced
through the thin roof of the mandibular fossa when one bites hard Common Joint Injuries
foods such as nuts or hard candies. The superior compartment
also allows this joint to glide from side to side. As the posterior For most of us, sprains and dislocations are the most common
teeth are drawn into occlusion during grinding, the mandible trauma-induced joint injuries, but cartilage injuries are equally
moves with a side-to-side movement called lateral excursion (Fig- threatening to athletes.
ure 8.12c). This lateral jaw movement is unique to mammals and
it is readily apparent in horses and cows as they chew. Cartilage Tears
Those who overdo various forms of exercise may end up feel-
ClinicAL ing the snap and pop of their overstressed cartilage. Although
H om e o stati c
most cartilage injuries involve tearing of the knee menisci, tears
I m bal an ce 8 .2
and overuse damage to the articular cartilages of other joints is
Dislocations of the TMJ occur more readily than any other 8
becoming increasingly common in young athletes.
joint dislocation because of the shallow socket in the joint. Cartilage tears typically occur when a meniscus is subjected
Even a deep yawn can dislocate it. This joint almost always dis- to compression and shear stress at the same time. Cartilage is
locates anteriorly, the condylar process of the mandible end- avascular and it rarely can obtain sufficient nourishment to
ing up in a skull region called the infratemporal fossa (Figure repair itself, so it usually stays torn. Cartilage fragments (called
8.12a). In such cases, the mouth remains wide open. To realign loose bodies) can interfere with joint function by causing the
a dislocated TMJ, the physician places his or her thumbs in the joint to lock or bind, so most sports physicians recommend that
patient’s mouth between the lower molars and the cheeks, and the damaged cartilage be removed. Today, this can be done by
then pushes the mandible inferiorly and posteriorly. arthroscopic surgery (ar-thro-skop′ik; “looking into joints”), a
At least 5% of Americans suffer from painful TMJ disorders, procedure that enables patients to be out of the hospital the same
the most common symptoms of which are pain in the ear and day. The arthroscope, a small instrument bearing a tiny lens and
face, tenderness of the jaw muscles, popping sounds when the fiber-optic light source, enables the surgeon to view the joint
mouth opens, and joint stiffness. Usually caused by painful interior, as in Figure 8.13. The surgeon can then repair a liga-
spasms of the chewing muscles, TMJ disorders often afflict peo- ment or remove cartilage fragments through one or more tiny
ple who grind their teeth; however, it can also result from jaw slits, minimizing tissue damage and scarring. Removal of part of
trauma or from poor occlusion of the teeth. Treatment usually a meniscus does not severely impair knee joint mobility, but the
focuses on getting the jaw muscles to relax by using massage, joint is definitely less stable. Removal of the entire meniscus is an
muscle-relaxant drugs, heat or cold, or stress reduction tech- invitation to early onset of osteoarthritis. For younger patients
niques. For tooth grinders, use of a bite plate during sleep may a meniscal transplant may be an option to replace irreparably
be recommended. ✚
Check Your Understanding
Femur
9. 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? Meniscus

For answers, see Answers Appendix.

ClinicAL
Joints are easily
8.6 Tear in
meniscus
damaged by injury, inflammation, and
degeneration
Tibia
Learning Objectives
Name the most common joint injuries and discuss the
symptoms and problems associated with each.
Compare and contrast the common types of arthritis. Figure 8.13 Arthroscopic photograph of a torn medial
Describe the cause and consequences of Lyme disease. meniscus. (Courtesy of the author’s tennis game.)

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 292 Unit 2 Covering, Support, and Movement of the Body

damaged cartilage. In the future, a tissue-engineered meniscus North America. One in five of us suffers its ravages. To a greater
grown from your own stem cells may be implanted instead. or lesser degree, all forms of arthritis have the same initial symp-
toms: pain, stiffness, and swelling of the joint.
Sprains Acute forms of arthritis usually result from bacterial inva-
In a sprain, the ligaments reinforcing a joint are stretched or sion and are treated with antibiotics. Chronic forms of arthritis
torn. Common sites of sprains are the ankle, the knee, and the include osteoarthritis, rheumatoid arthritis, and gouty arthritis.
lumbar region of the spine. Partially torn ligaments will repair Osteoarthritis Osteoarthritis (OA) is the most common
themselves, but they heal slowly because ligaments are so poorly chronic arthritis. A chronic degenerative condition, OA is
vascularized. Sprains tend to be painful and immobilizing. often called “wear-and-tear arthritis.” OA is most prevalent in
When ligaments are completely torn, there are three options: the aged and is probably related to the normal aging process
● The torn ends of the ligament can be sewn together. This is dif- (although it is seen occasionally in younger people and some
ficult because trying to sew the hundreds of fibrous strands of a forms have a genetic basis). More women than men are affected,
ligament together is like trying to sew two hairbrushes together. and nearly all of us will develop this condition by the age of 80.
● Certain ligaments, like the anterior cruciate ligament, are Current theory holds that normal joint use prompts the
best repaired by replacing them with grafts. For example, a release of (metalloproteinase) enzymes that break down articu-
piece of tendon from a muscle can be attached to the articu- lar cartilage, especially its collagen fibrils. In healthy individuals,
lating bones. this damaged cartilage is eventually replaced, but in people with
OA, more cartilage is destroyed than replaced. Although its spe-
● For many ligaments, such as the knee’s medial collateral liga-
8 cific cause is unknown, OA may reflect the cumulative effects of
ment, we’ve come to realize that time and immobilization are
years of compression and abrasion acting at joint surfaces, caus-
just as effective as any surgical option.
ing excessive amounts of the cartilage-destroying enzymes to be
released. The result is softened, roughened, pitted, and eroded
Dislocations articular cartilages. Because this process occurs most where
A dislocation (luxation) occurs when bones are forced out of an uneven orientation of forces cause extensive microdamage,
alignment. It is usually accompanied by sprains, inflammation, badly aligned or overworked joints are likely to develop OA.
and difficulty in moving the joint. Dislocations may result from As the disease progresses, the exposed bone tissue thickens
serious falls and are common contact sports injuries. Joints of and forms bony spurs (osteophytes) that enlarge the bone ends
the jaw, shoulders, fingers, and thumbs are most commonly dis- and may restrict joint movement. Patients complain of stiffness
located. Like fractures, dislocations must be reduced; that is, the on arising that lessens somewhat with activity. The affected
bone ends must be returned to their proper positions by a phy- joints may make a crunching noise, called crepitus (krep′ĭ-tus),
sician. Subluxation is a partial dislocation of a joint. as they move and the roughened articular surfaces rub together.
Repeat dislocations of the same joint are common because the The joints most often affected are those of the cervical and lum-
initial dislocation stretches the joint capsule and ligaments. The bar spine and the fingers, knuckles, knees, and hips.
resulting loose capsule provides poor reinforcement for the joint. The 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 activ-
Inflammatory and Degenerative Conditions ity to keep the joints mobile. Glucosamine and chondroitin sulfate,
Inflammatory conditions that affect joints include bursitis and nutritional supplements consisting of macromolecules normally
tendonitis, various forms of arthritis, and Lyme disease. present in cartilage, have been widely used by arthritis sufferers.
However, several recent studies suggest that these supplements are
Bursitis and Tendonitis no more effective than placebos. Osteoarthritis is rarely crippling,
Bursitis is inflammation of a bursa and is usually caused by a blow but it can be, particularly when the hip or knee joints are involved.
or friction. Falling on one’s knee may result in a painful bursitis of Rheumatoid Arthritis Rheumatoid arthritis (RA) (roo′mah-
the prepatellar bursa, known as housemaid’s knee or water on the toid) is a chronic inflammatory disorder. It usually arises
knee. Prolonged leaning on one’s elbows may damage the bursa between the ages of 30 and 50, but can occur at any age. It affects
close to the olecranon, producing student’s elbow, or olecranon three times as many women as men. While not as common as
bursitis. Severe cases are treated by injecting anti-inflammatory osteoarthritis, rheumatoid arthritis affects millions, about 1%
drugs into the bursa. If excessive fluid accumulates, removing of all people.
some fluid by needle aspiration may relieve the pressure. In the early stages of RA, joint tenderness and stiffness are
Tendonitis is inflammation of tendon sheaths, typically caused common. Many joints, particularly the small joints of the fin-
by overuse. Its symptoms (pain and swelling) and treatment (rest, gers, wrists, ankles, and feet, are afflicted at the same time and
ice, and anti-inflammatory drugs) mirror those of bursitis. bilaterally. For example, if the right elbow is affected, most likely
the left elbow is also affected. The course of RA is variable and
Arthritis marked by flare-ups (exacerbations) and remissions (rheu-
The term arthritis describes over 100 different types of inflam- mat = susceptible to change). Along with pain and swelling,
matory or degenerative diseases that damage the joints. In all its manifestations may include anemia, osteoporosis, muscle
its forms, arthritis is the most widespread crippling disease in weakness, and cardiovascular problems.

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 A C l os e r Loo k Clinical

Joints: From Knights in Shining Armor to Bionic Humans

The technology for fashioning joints in prostheses work loose over time, researchers ●  steochondral grafting: Healthy bone
O
medieval suits of armor developed over are seeking to enhance the fit between and cartilage are removed from one part
centuries. The technology for creating implant and bone. One solution is to of the body and transplanted to the
the prostheses (artificial joints) used in strengthen the cement that binds them. injured joint.
medicine today developed, in relative terms, Another solution is to use a cementless ● Autologous chondrocyte implantation:
in a flash—less than 70 years. Unlike the prosthesis, which allows the bone to grow Healthy chondrocytes are removed from
joints in medieval armor, which was worn into its surface, fixing it in place. For this to the body and seeded onto a supporting
outside the body, today’s artificial joints happen, a precise fit in the prosthesis and matrix of tissue-engineered collagen.
must function inside the body. The history the bone must be achieved, something at When subjected to mechanical pressure
of joint prostheses dates to the 1940s and which surgical robots such as ROBODOC in the lab, the cells produce new
1950s, when World War II and the Korean excel. cartilage, which is then implanted.
War left large numbers of wounded who Dramatic changes are also occurring in ● Mesenchymal stem cell regeneration:
needed artificial limbs. Today, nearly 1 the way artificial joints are made. Computer-
Undifferentiated mesenchymal cells are
million Americans per year receive a total aided design and manufacturing techniques
removed from bone marrow and placed
joint replacement, mostly because of the have significantly reduced the time and cost
in a gel, which is packed into an area of
destructive effects of osteoarthritis or of creating individualized joints.
eroded cartilage.
rheumatoid arthritis. Joint replacement therapy is coming of
To produce durable, mobile joints requires age, but equally exciting are techniques that These techniques offer hope for younger
substances that are strong, nontoxic, call on the ability of the patient’s own tissues patients, since they could stave off the need
and resistant to the corrosive effects of to regenerate. for a joint prosthesis for several years.
organic acids in blood. In 1963, Sir John ● Bone marrow stimulation: Small holes And so, through the centuries, the focus
Charnley, an English orthopedic surgeon, poked through to the bone marrow has shifted from jointed armor to artificial
revolutionized the therapy of arthritic hips allow mesenchymal stem cells from the joints that can be put inside the body to
with an artificial hip design that is still in use bone marrow to migrate into the joint restore lost function. Modern technology
today. His device consisted of a metal ball and produce new cartilage. has accomplished what the armor designers
on a stem and a cup-shaped polyethylene of the Middle Ages never dreamed of.
plastic socket anchored to the pelvis by
methyl methacrylate cement. This cement
proved to be exceptionally strong and
relatively problem free. Hip prostheses were
followed by knee prostheses, but not until
10 years later did smoothly operating total
knee joint replacements become a reality.
Today, the metal parts of the prostheses are
strong cobalt and titanium alloys, and the
number of knee replacements equals the
number of hip replacements.
Replacements are now available for many
other joints, including fingers, elbows, and
shoulders. Total hip and knee replacements
last about 10 to 15 years in elderly patients
who do not excessively stress the joint. Most
such operations are done to reduce pain and
restore about 80% of original joint function.
Replacement joints are not yet strong or
durable enough for young, active people,
but making them so is a major goal. Since
A hip prosthesis. X ray of right knee showing total knee
replacement prosthesis.

RA is an autoimmune disease—a disorder in which the in cartilage, joint fluid, and other connective tissues), and the
body’s immune system attacks its own tissues. The initial trigger immune system, once activated, attempts to destroy both.
for this reaction is unknown, but various bacteria and viruses RA begins with inflammation of the synovial membrane
have been suspect. Perhaps these microorganisms bear mol- (synovitis) of the affected joints. Inflammatory cells (lympho-
ecules similar to some naturally present in the joints (possibly cytes, macrophages, and others) migrate into the joint cavity
glycosaminoglycans, which are complex carbohydrates found from the blood and unleash a deluge of inflammatory chemicals

293

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 294 Unit 2 Covering, Support, and Movement of the Body

that destroy body tissues when released in large amounts. Syno- Untreated gout can be very destructive; the articulating bone
vial fluid accumulates, causing joint swelling, and in time, the ends fuse and immobilize the joint. Fortunately, several drugs
inflamed synovial membrane thickens into a pannus (“rag”), (colchicine, nonsteroidal anti-inflammatory drugs, glucocorti-
an abnormal tissue that clings to the articular cartilages. The coids, and others) that terminate or prevent gout attacks are
pannus erodes the cartilage (and sometimes the underly- available. Patients are advised to drink plenty of water and to
ing bone) and eventually scar tissue forms and connects the avoid excessive alcohol consumption (which promotes uric acid
bone ends. Later this scar tissue ossifies and the bone ends fuse overproduction) and foods high in purine-containing nucleic
together, immobilizing the joint. This end condition, called acids, such as liver, kidneys, and sardines.
ankylosis (ang″kĭ-lo′sis; “stiff condition”), often produces bent,
deformed fingers (Figure 8.14). Not all cases of RA progress Lyme Disease
to the severely crippling ankylosis stage, but all cases do involve Lyme disease is an inflammatory disease caused by spirochete
restriction of joint movement and extreme pain. bacteria transmitted by the bite of ticks that live on mice and
The goal of current RA treatment is to go beyond simply allevi- deer. It often results in joint pain and arthritis, especially in the
ating the symptoms and instead to disrupt the relentless destruc- knees, and is characterized by a skin rash, flu-like symptoms,
tion of the joints. Steroidal and nonsteroidal anti-inflammatory and foggy thinking. If untreated, neurological disorders and
drugs decrease pain and inflammation, increasing joint mobil- irregular heartbeat may ensue.
ity. More powerful immune suppressants (such as methotrexate) Because symptoms vary from person to person, the disease is
act to slow the autoimmune reaction. Several biologic agents hard to diagnose. Antibiotic therapy is the usual treatment, but
are available to block the action of inflammatory chemicals. An it takes a long time to kill the infecting bacteria.
8
important target of many of these agents is an inflammatory
chemical called tumor necrosis factor. Together, these drugs can Check Your Understanding
dramatically slow the course of RA. As a last resort, replacing the 10. What does the term “arthritis” mean?
joint with a joint prosthesis (artificial joint) may be an option to 11. How would you determine by looking at someone suffering
restore function (see A Closer Look, p. 293). Indeed, some RA from arthritis if he or she has OA or RA?
sufferers have over a dozen artificial joints. 12. What is the cause of Lyme disease?
Gouty Arthritis Uric acid, a normal waste product of nucleic For answers, see Answers Appendix.
acid metabolism, is ordinarily excreted in urine without any prob-
lems. However, when blood levels of uric acid rise excessively (due
to its excessive production or slow excretion), it may be depos- Developmental Aspects of Joints
ited as needle-shaped urate crystals in the soft tissues of joints. An
inflammatory response follows, leading to an agonizingly painful
attack of gouty arthritis (gow′te), or gout. The initial attack typi- As bones form from mesenchyme in the embryo, the joints
cally affects one joint, often at the base of the great toe. develop in parallel. By week 8, the synovial joints resemble adult
Gout is far more common in men than in women because joints in form and arrangement, and synovial fluid is being
men naturally have higher blood levels of uric acid (perhaps secreted. During childhood, a joint’s size, shape, and flexibility
because estrogens increase the rate of its excretion). Because are modified by use. Active joints have thicker capsules and liga-
gout seems to run in families, genetic factors are definitely ments, and larger bony supports.
implicated. Injuries aside, relatively few interferences with joint func-
tion occur until late middle age. Eventually advancing years
take their toll—ligaments and tendons shorten and weaken.
The intervertebral discs become more likely to herniate, and
osteoarthritis rears its ugly head. Many people have osteoarthri-
tis by the time they are in their 70s. The middle years also see an
increased incidence of rheumatoid arthritis.
Exercise that coaxes joints through their full range of motion,
such as regular stretching and aerobics, is the key to postpon-
ing the immobilizing effects of aging on ligaments and tendons,
to keeping cartilages well nourished, and to strengthening the
muscles that stabilize the joints. The key word for exercising
is “prudently,” because excessive or abusive use of the joints
guarantees early onset of osteoarthritis. The buoyancy of water
relieves much of the stress on weight-bearing joints, and people
who swim or exercise in a pool often retain good joint function
as long as they live. As with so many medical problems, it is
easier to prevent joint problems than to cure or correct them.

Figure 8.14 A hand deformed by rheumatoid arthritis. ● ● ●

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 Chapter 8 Joints 295
The importance of joints is obvious: The skeleton’s ability to movements that joints allow, we are ready to consider how the
protect other organs and to move smoothly reflects their pres- muscles attached to the skeleton cause body movements by act-
ence. Now that we are familiar with joint structure and with the ing across its joints.

C h a p t e r S u m m a ry

For more chapter study tools, go to the Study Area Movements Allowed by Synovial Joints (pp. 278–280)
of . 7. When a skeletal muscle contracts, the insertion (movable
There you will find: attachment) moves toward the origin (immovable attachment).
• Interactive Physiology • A&PFlix 8. Synovial joints differ in their range of motion. Motion may be
nonaxial (gliding), uniaxial (in one plane), biaxial (in two planes),
• Practice Anatomy Lab • PhysioEx
or multiaxial (in all three planes).
• Videos, Practice Quizzes and Tests, 9. Three common types of movements can occur when muscles
MP3 Tutor Sessions, Case Studies, and much more! contract across joints: (a) gliding movements, (b) angular
movements (which include flexion, extension, abduction,
1. Joints, or articulations, are sites where bones meet. Their adduction, and circumduction), and (c) rotation.
functions are to hold bones together and to allow various degrees 10. Special movements include supination and pronation, inversion
of skeletal movement. and eversion, protraction and retraction, elevation and 8
depression, opposition, dorsiflexion and plantar flexion.
8.1 Joints are classified into three structural and three
functional categories (p. 271) Types of Synovial Joints (p. 280)
1. Joints are classified structurally as fibrous, cartilaginous, or synovial. 11. The six major categories of synovial joints are plane joints
They are classed functionally as synarthrotic, amphiarthrotic, or (nonaxial movement), hinge joints (uniaxial), pivot joints
diarthrotic. Only synovial joints have a joint cavity. (uniaxial, rotation permitted), condylar joints (biaxial with
angular movements in two planes), saddle joints (biaxial, like
8.2 In fibrous joints, the bones are connected by fibrous condylar joints, but with freer movement), and ball-and-socket
tissue (p. 272) joints (multiaxial and rotational movement).
1. Sutures/syndesmoses/gomphoses. The major types of fibrous
joints are sutures, syndesmoses, and gomphoses. Nearly all
8.5 Five examples illustrate the diversity of synovial
fibrous joints are synarthrotic.
joints (pp. 280–291)
1. The knee joint is the largest joint in the body. It is a hinge joint
8.3 In cartilaginous joints, the bones are connected by formed by the articulation of the tibial and femoral condyles
cartilage (p. 273) (and anteriorly by the patella and patellar surface of the femur).
1. Synchondroses/symphyses. Cartilaginous joints include Extension, flexion, and (some) rotation are allowed. Its articular
synchondroses and symphyses. Synchondroses are synarthrotic; surfaces are shallow and condylar. C-shaped menisci deepen the
all symphyses are amphiarthrotic. articular surfaces. The joint cavity is enclosed by a capsule only
on the sides and posterior aspect. Several ligaments help prevent
8.4 Synovial joints have a fluid-filled joint cavity displacement of the joint surfaces. Muscle tone of the quadriceps
(pp. 274–280) and semimembranosus muscles is important in knee stability.
1. Most body joints are synovial joints, all of which are diarthrotic. 2. The shoulder joint is a ball-and-socket joint formed by the
glenoid cavity of the scapula and the humeral head. The most
General Structure (pp. 274–275) freely movable joint of the body, it allows all angular and
2. All synovial joints have: a joint cavity enclosed by a fibrous layer rotational movements. Its articular surfaces are shallow. Its
lined with synovial membrane and reinforced by ligaments; capsule is lax and poorly reinforced by ligaments. The tendons of
articulating bone ends covered with articular cartilage; and the biceps brachii and rotator cuff muscles help to stabilize it.
synovial fluid in the joint cavity. Some (e.g., the knee) contain 3. The elbow joint is a hinge joint in which the ulna (and radius)
fibrocartilage discs that absorb shock. articulates with the humerus, allowing flexion and extension.
Its articular surfaces are highly complementary and are the most
Bursae and Tendon Sheaths (p. 275) important factor contributing to joint stability.
3. Bursae are fibrous sacs lined with synovial membrane and 4. The hip joint is a ball-and-socket joint formed by the acetabulum
containing synovial fluid. Tendon sheaths are similar to bursae of the hip bone and the femoral head. It is highly adapted for
but are cylindrical structures that surround muscle tendons. Both weight bearing. Its articular surfaces are deep and secure. Its
allow adjacent structures to move smoothly over one another. capsule is heavy and strongly reinforced by ligaments.
5. The temporomandibular joint is formed by (1) the condylar
Factors Influencing the Stability of Synovial Joints (p. 277) process of the mandible and (2) the mandibular fossa and
4. Articular surfaces providing the most stability have large surfaces articular tubercle of the temporal bone. This joint allows both
and deep sockets and fit snugly together. a hingelike opening and closing of the mouth and an anterior
5. Ligaments prevent undesirable movements and reinforce the joint. gliding of the mandible. It often dislocates anteriorly and exhibits
6. The tone of muscles whose tendons cross the joint is the most a number of TMJ disorders.
important stabilizing factor in many joints.

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 296 Unit 2 Covering, Support, and Movement of the Body

7. Rheumatoid arthritis, the most crippling arthritis, is an

8.6 Joints are easily damaged by injury, inflammation,
autoimmune disease involving severe inflammation of the joints.
and degeneration (pp. 291–294)
8. Gouty arthritis, or gout, is joint inflammation caused by the
1. Cartilage injuries, particularly of the knee, are common in deposit of urate salts in soft joint tissues.
contact sports and may result from excessive compression and 9. Lyme disease is an infectious disease caused by the bite of a tick
shear stress. The avascular cartilage is unable to repair itself. infected with spirochete bacteria.
2. Sprains involve stretching or tearing of joint ligaments. Because
ligaments are poorly vascularized, healing is slow. Developmental Aspects of Joints (pp. 294–295)
3. Dislocations involve displacement of the articular surfaces of 1. Joints form from mesenchyme and in tandem with bone
bones. They must be reduced. development in the embryo.
4. Bursitis and tendonitis are inflammations of a bursa and a tendon 2. Excluding traumatic injury, joints usually function well until
sheath, respectively. late middle age, at which time symptoms of connective tissue
5. Arthritis is joint inflammation or degeneration accompanied stiffening and osteoarthritis begin to appear. Prudent exercise
by stiffness, pain, and swelling. Acute forms generally result delays these effects, whereas excessive exercise promotes the early
from bacterial infection. Chronic forms include osteoarthritis, onset of arthritis.
rheumatoid arthritis, and gouty arthritis.
6. Osteoarthritis is a degenerative condition most common in the
aged. Spine, knees, hips, knuckles, and fingers are most affected.

8 Review Questions
Multiple Choice/Matching Short Answer Essay Questions
(Some questions have more than one correct answer. Select the best 8. Define joint.
answer or answers from the choices given.) 9. While the fingers can exhibit flexion and extension and other
1. Match the key terms to the appropriate descriptions. angular motions, the thumb has much greater freedom. Why?
10. Compare the structure, function, and common body locations of
Key: (a) fibrous joints (b)  cartilaginous joints bursae and tendon sheaths.
(c) synovial joints 11. Joint movements may be nonaxial, uniaxial, biaxial, or multiaxial.
____ (1) exhibit a joint cavity Define what each of these terms means.
____ (2) types are sutures and syndesmoses 12. Compare and contrast the paired movements of flexion and
____ (3) bones connected by collagen fibers extension with adduction and abduction.
____ (4) types include synchondroses and symphyses 13. How does rotation differ from circumduction?
____ (5) all are diarthrotic 14. Name two types of uniaxial, biaxial, and multiaxial joints.
____ (6) many are amphiarthrotic 15. What is the specific role of the menisci of the knee? Of the
____ (7) bones connected by a disc of hyaline cartilage or anterior and posterior cruciate ligaments?
fibrocartilage 16. Many inflammations of joint areas can be treated by injections of
____ (8) nearly all are synarthrotic cortisone into the area. Why don’t we continually get injections
____ (9) shoulder, hip, jaw, and elbow joints rather than operations?
2. A fibrous joint that is a peg-in-socket is called a (a) syndesmosis, 17. Why are sprains and cartilage injuries a particular problem?
(b) suture, (c) synchondrosis, (d) gomphosis joint. 18. List the functions of the following elements of a synovial joint:
3. Anatomical characteristics shared by all synovial joints include fibrous layer of the capsule, synovial fluid, articular cartilage.
all except (a) articular cartilage, (b) a joint cavity, (c) an articular
capsule, (d) presence of fibrocartilage. C l i n i cAL 
4. Articular cartilage found at the ends of the long bones serves to Critical Thinking
(a) attach tendons, (b) produce red blood cells (hemopoiesis), and Clinical Application
(c) provide a smooth surface at the ends of synovial joints, Questions
(d) form the synovial membrane. 1. Sonya worked cleaning homes for 30 years so she could send her
5. The description “Articular surfaces deep and secure; capsule two children to college. Several times, she had been forced to call
heavily reinforced by ligaments and muscle tendons; extremely her employers to tell them she could not come in to work because
stable joint” best describes (a) the elbow joint, (b) the hip joint, one of her kneecaps was swollen and painful. What is Sonya’s
(c) the knee joint, (d) the shoulder joint. condition, and what probably caused it?
6. Ankylosis means (a) twisting of the ankle, (b) tearing of 2. As Jose was running down the road, he tripped and his left ankle
ligaments, (c) displacement of a bone, (d) immobility of a joint twisted violently to the side. When he picked himself up, he
due to fusion of its articular surfaces. was unable to put any weight on that ankle. The diagnosis was
7. An autoimmune disorder in which joints are affected bilaterally severe dislocation and sprains of the left ankle. The orthopedic
and which involves pannus formation and gradual joint surgeon stated that she would perform a closed reduction of the
immobilization is (a) bursitis, (b) gout, (c) osteoarthritis, dislocation and attempt ligament repair by using arthroscopy.
(d) rheumatoid arthritis.

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 Chapter 8 Joints 297
(a) Is the ankle joint normally a stable joint? (b) What does its 4. Grace heard on the evening TV news that the deer population
stability depend on? (c) What is a closed reduction? (d) Why is in her state had been increasing rapidly in the past few years and
ligament repair necessary? (e) What does arthroscopy entail? it was common knowledge that deer walked the streets at night.
(f) How will the use of this procedure minimize Jose’s After the program, she suddenly exclaimed, “So that’s why those
recuperation time (and suffering)? three boys in my son’s class got Lyme disease last year.” Explain
3. A nurse is instructing the patient care assistants (PCAs) on what she meant by that comment.
transfer techniques. For patients needing to be slid toward the 5. Tony Bowers, an exhausted biology student, was attending a
head of the bed, the nurse tells the PCAs to use a draw sheet lecture. After 30 minutes or so, he lost interest and began to doze.
under the patient’s torso. She tells them to avoid pulling on their As the lecture ended, the hubbub aroused him and he let go with
hands or arms. Based on your knowledge of the shoulder joint, a tremendous yawn. To his great distress, he couldn’t close his
explain why pulling on the extremities should be avoided. mouth—his lower jaw was “stuck” open. What do you think had
happened?

At t h e C l i n i c

Related Clinical Terms

Ankylosing spondylitis (ang′kı̆-lōz″ing spon″dı̆-li′tis; ankyl = crooked, knee when the leg is extended (in climbing stairs, for example). May
bent; spondyl = vertebra) A variant of rheumatoid arthritis that chiefly result when the quadriceps femoris, the main group of muscles on the
affects males; it usually begins in the sacroiliac joints and progresses anterior thigh, pulls unevenly on the patella, persistently rubbing it
superiorly along the spine. The vertebrae become interconnected by against the femur in the knee joint; often corrected by exercises that
fibrous tissue, causing the spine to become rigid (“poker back”). strengthen weakened parts of the quadriceps muscles.
Arthrology (ar-throl′o-je; logos = study) The study of joints. Rheumatism A lay term referring to disease involving muscle or joint pain;
Arthroplasty (“joint reforming”) Replacing a diseased joint with an may be used to apply to arthritis, bursitis, etc.
artificial joint. Synovitis (sin″o-vi′tis) Inflammation of the synovial membrane of a
Chondromalacia patellae (kon-dro-mal-a′sı̆-ah; “softening of cartilage by joint. Caused by injury, infection, or arthritis. Excess synovial fluid
the patella”) Damage and softening of the articular cartilages on the accumulates in the joint cavity, a condition called effusion that causes
posterior patellar surface and the anterior surface of the distal femur; the joint to swell, limiting joint movement.
most often seen in adolescent athletes. Produces a sharp pain in the

Clinical Case Study 2. N

 ame the six distinguishing features that
define the structural classification of the joint
Joints involved in this injury.
In the previous chapter, you met Kayla Tanner,
3. It is important that there is synovial fluid in
a 45-year-old mother of four who suffered a
Mrs. Tanner’s joint space. Explain the role of
dislocated right hip in the bus accident on
synovial fluid.
Route 91. Prior to the closed reduction, the
doctors noted that her right thigh was flexed 4. Surgeons had to remove a portion of
at the hip, adducted, and medially rotated. Mrs. Tanner’s acetabular labrum. What is this
After the reduction, the hip was put through structure and what function does it supply at
a gentle range of motion (ROM) to assess the this joint?
joint. A widened joint space in the postreduction X ray showed that 5. The doctors noted that Mrs. Tanner’s thigh was flexed at the hip,
the reduction was not complete, but no bone fragments were visible adducted, and medially rotated. Describe what this means in terms of
in the joint space. Mrs. Tanner was scheduled for immediate surgery. the position of her leg.
The surgeons discovered that the acetabular labrum was detached
from the rim of the acetabulum and was lying deep within the joint 6. Hip dislocations can be classified as anterior or posterior depending
space. The detached portion of the labrum was excised, and the hip was on which direction the head of the femur is facing after it dislocates.
surgically reduced. During the early healing phase (first two weeks), Based on the description you provided in question 5, which type of
Mrs. Tanner was kept in traction with the hip abducted. dislocation did Mrs. Tanner suffer?

1. Mrs. Tanner’s hip joint is a diarthrotic (freely movable) joint 7. In order to assess the joint as part of Mrs. Tanner’s rehabilitation,
which is stabilized by two important structures. What are these clinicians would want to assess all of the movements that normally occur
structures? at the hip. List all the movements that the clinicians will need to assess.
For answers, see Answers Appendix.

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