SKELETAL SYSTEM

9 O U T L I N E

9.1 Articulations (Joints)

9.1a Classification of Joints
9.2 Fibrous Joints
9.2a Gomphoses 254
9.2b Sutures 255
254
253
253

Articulations 9.2c Syndesmoses 255

9.3 Cartilaginous Joints
9.3a Synchondroses 255
9.3b Symphyses 256
255

9.4 Synovial Joints 256

9.4a General Anatomy of Synovial Joints 257
9.4b Types of Synovial Joints 258
9.4c Movements at Synovial Joints 260
9.5 Selected Articulations in Depth 265
9.5a Joints of the Axial Skeleton 265
9.5b Joints of the Pectoral Girdle and Upper Limbs 268
9.5c Joints of the Pelvic Girdle and Lower Limbs 274
9.6 Disease and Aging of the Joints 282
9.7 Development of the Joints 284

MODULE 5: SKELE TAL SYSTEM

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 Chapter Nine Articulations 253

ur skeleton protects vital organs and supports soft tissues. Its The motion permitted at a joint ranges from no movement (e.g.,
O marrow cavity is the source of new blood cells. When it inter-
acts with the muscular system, the skeleton helps the body move.
where some skull bones interlock at a suture) to extensive movement
(e.g., at the shoulder, where the arm connects to the scapula). The
Although bones are slightly flexible, they are too rigid to bend so they structure of each joint determines its mobility and its stability. There is
meet at joints, which anatomists call articulations. In this chapter, an inverse relationship between mobility and stability in articulations.
we examine how bones articulate and may allow some freedom of The more mobile a joint is, the less stable it is; and the more stable
movement, depending on the shapes and supporting structures of a joint is, the less mobile it is. Figure 9.1 illustrates the “tradeoff”
the various joints. between mobility and stability for various joints.

9.1a Classification of Joints

Joints are categorized structurally on the basis of the type of con-
9.1 Articulations (Joints) nective tissue that binds the articulating surfaces of the bones, and
Learning Objectives: whether a space occurs between the articulating bones:
1. Describe the general structure of articulations. ■ A fibrous (fı̄  ́ brŭs) joint occurs where bones are held
2. Discuss the connection between degree of movement and together by dense regular (fibrous) connective tissue.
joint structure. ■ A cartilaginous (kar-ti-laj  ́ i-nŭs; cartilago = gristle) joint
3. Identify both the structural and functional classifications of occurs where bones are joined by cartilage.
joints. ■ A synovial (si-nō  ́vē-ă l) joint has a fluid-filled joint cavity
that separates the cartilage-covered articulating surfaces of
A joint, or articulation (ar-tik-ū-lā  ́shŭn), is the place of con-
the bones. The articulating surfaces are enclosed within a
tact between bones, between bone and cartilage, or between bones
capsule, and the bones are also joined by various ligaments.
and teeth. Bones are said to articulate with each other at a joint.
The scientific study of joints is called arthrology (ar-throl  ́ō-jē; Joints may also be classified functionally based on the extent
arthron = joint, logos = study). of movement they permit:
■ A synarthrosis (sin  ́ar-thrō  ́sis; pl., sin  ́ar-thrō  ́sēz; syn =
joined together) is an immobile joint.
■ An amphiarthrosis (am  ́ fi-ar-thrō  ́sis; pl., -sēz; amphi =
Study Tip! around) is a slightly mobile joint.
You can figure out the names of most joints by piecing together ■ A diarthrosis (dı̄-ar-thrō  ́sis; pl., -sēz; di = two) is a freely
the names of the bones that form them. For example, the glenohumeral mobile joint.
joint is where the glenoid cavity of the scapula meets the head of the The following discussion of articulations is based on their
humerus, and the sternoclavicular joint is where the manubrium of the structural classification, with functional categories included as
sternum articulates with the sternal end of the clavicle. appropriate. As you read about the various types of joints, it may help
you to refer to the summary of joint classifications in table 9.1.

Mobility

Most mobile Immobile

Glenohumeral joint Hip joint Elbow joint Intervertebral joints Suture

(shoulder)

Stability

Very unstable Most stable

Figure 9.1
Relationship Between Mobility and Stability in Joints. In every joint, there is a “tradeoff” between the relative amounts of mobility and
stability. The more mobile the joint, the less stable it is. Conversely, the more stable the joint, the less mobile it is. Note how the glenohumeral
(shoulder) joint is very mobile but not very stable, while a suture is immobile and yet very stable.

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 254 Chapter Nine Articulations

Table 9.1 Joint Classifications

Structural Structural Structural Category Example Functional Classification
Classification Characteristics
Fibrous Dense regular connective Gomphosis: Periodontal Tooth to jaw Synarthrosis (immobile)
tissue holds together the membranes hold tooth to
ends of bones and bone bony jaw
parts; no joint cavity
Suture: Dense regular Lambdoid suture (connects Synarthrosis (immobile)
connective tissue connects occipital and parietal bones)
skull bones
Syndesmosis: Dense regular Articulation between radius Amphiarthrosis (slightly mobile)
connective tissue fibers and ulna, and between tibia
(interosseous membrane) and fibula
between bones
Cartilaginous Pad of cartilage is wedged Synchondrosis: Hyaline Epiphyseal plates in growing Synarthrosis (immobile)
between the ends of bones; cartilage plate between bones; costochondral joints
no joint cavity bones
Symphysis: Fibrocartilage Pubic symphysis; Amphiarthrosis (slightly mobile)
pad between bones intervertebral disc articulations
Synovial Ends of bones covered Plane joint: Flattened or Plane joint: Intercarpal joints, Diarthrosis (freely mobile)
with articular cartilage; slightly curved faces slide intertarsal joints
joint cavity separates the across one another
articulating bones; enclosed Hinge joint: Permits angular Hinge joint: Elbow joint
by a joint capsule, lined by a movements in a single
synovial membrane; contains plane
synovial fluid
Pivot joint: Permits rotation Pivot joint: Atlantoaxial joint
only
Biaxial Diarthrosis (freely mobile)
Condylar joint: Oval Condylar joint: MP
articular surface on one (metacarpophalangeal) joints
bone closely interfaces with
a depressed oval surface on
another bone
Saddle joint: Saddle-shaped Saddle joint: Articulation
articular surface on one between carpal and first
bone closely interfaces metacarpal bone
with depressed surface on
another bone

Multiaxial (triaxial) Ball-and-socket joint: Diarthrosis (freely mobile)

Ball-and-socket joint: Glenohumeral joint, hip joint
Round head of one bone
rests within cup-shaped
depression in another bone

W H AT D I D Y O U L E A R N? the articulating bones). The three types of fibrous joints are gom-
●
1 What type of articulation uses dense regular connective tissue to phoses, sutures, and syndesmoses (figure 9.2).
bind the bones?
9.2a Gomphoses
●
2 What term is used to describe immobile joints?
A gomphosis (gom-fō  ́sis; pl., -sēz; gomphos = bolt, osis = condi-
tion) resembles a “peg in a socket.” The only gomphoses in the
human body are the articulations of the roots of individual teeth
with the sockets of the mandible and the maxillae. A tooth is held
firmly in place by a fibrous periodontal (per  ́ē-ō-don  ́tăl; peri =
9.2
9.2 Fibrou
Fibrous
us Joints
Joints around, odous = tooth) membrane. This joint is functionally clas-
Learning Objectives: sified as a synarthrosis.
The reasons orthodontic braces can be painful and take a
1. Describe the characteristics of the three types of fibrous joints.
long time to correctly position the teeth are related to the gom-
2. Identify locations of gomphoses, sutures, and syndesmoses
phosis architecture. The orthodontist’s job is to reposition these
in the body.
normally immobile joints through the use of bands, rings, and
Articulating bones are joined by dense regular connective braces. In response to these mechanical stressors, osteoblasts and
tissue in fibrous joints. Most fibrous joints are immobile or only osteoclasts work together to modify the alveolus, resulting in the
slightly mobile. Fibrous joints have no joint cavity (space between remodeling of the joint and the slow repositioning of the teeth.

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 Chapter Nine Articulations 255

Suture
Ulna

Radius

Syndesmosis
Root of (interosseous
tooth membrane)
Periodontal
membranes Gomphosis
Alveolar
process of
mandible

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

Figure 9.2
Fibrous Joints. Dense regular connective tissue binds the articulating bones in fibrous joints to prevent or severely restrict movement.
(a) A gomphosis is the immobile joint between a tooth and the jaw. (b) A suture is an immobile joint between bones of the skull.
(c) A syndesmosis permits slight mobility between the radius and the ulna.

9.2b Sutures
Sutures (soo  ́choor; sutura = a seam) are immobile fibrous joints 9.3 Cartilaginous Joints
(synarthoses) that are found only between certain bones of
Learning Objectives:
the skull. Sutures have distinct, interlocking, usually irregular
edges that both increase their strength and decrease the number 1. Discuss the characteristics of the two types of cartilaginous
of fractures at these articulations. In addition to joining bones, joints.
sutures permit the skull to grow as the brain increases in size 2. Name locations of synchondroses and symphyses in the body.
during childhood. In an older adult, the dense regular connec- The articulating bones in cartilaginous joints are attached
tive tissue in the suture becomes ossified, fusing the skull bones to each other by cartilage. These joints lack a joint cavity. The
together. When the bones have completely fused across the two types of cartilaginous joints are synchondroses and symphy-
suture line, these obliterated sutures become synostoses (sin- ses (figure 9.3).
os-tō  ́sēz; sing., -sis).

9.2c Syndesmoses 9.3a Synchondroses

An articulation in which bones are joined by hyaline cartilage
Syndesmoses (sin  ́dez-mō  ́sēz; sing., -sis; syndesmos = a fastening)
is called a synchondrosis (sin  ́ kon-drō  ́sis; pl., -sē z; chondros =
are fibrous joints in which articulating bones are joined by long
cartilage). Functionally, all synchondroses are immobile and thus
strands of dense regular connective tissue only. Because syndes-
are classified as synarthroses. The hyaline cartilage of epiphyseal
moses allow for slight mobility, they are classified as amphiar-
plates in children forms synchondroses that bind the epiphyses
throses. Syndesmoses are found between the radius and ulna, and
and the diaphysis of long bones. When the hyaline cartilage stops
between the tibia and fibula. The shafts of the two articulating
growing, bone replaces the cartilage, and a synchondrosis no
bones are bound side by side by a broad ligamentous sheet called
longer exists.
an interosseous membrane (or interosseous ligament). The interos-
The spheno-occipital synchondrosis is found between the
seous membrane provides a pivot point where the radius and ulna
body of the sphenoid and the basilar part of the occipital bone.
(or the tibia and fibula) can move against one another.
This synchondrosis fuses between 18 and 25 years of age, making
it a useful tool for assessing the age of a skull.
W H AT D I D Y O U L E A R N? Another synchondrosis is the attachment of the first rib
●
3 Describe the three types of fibrous joints, and name a place in the to the sternum by costal cartilage (called the first sternocostal joint).
body where each type is found. Here, the first rib and its costal cartilage (formed from hyaline

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 256 Chapter Nine Articulations

Costochondral joints
Epiphyseal plate (immobile joints between the CLINICAL VIEW
rib and its costal cartilage)
Joint between
first rib and
Costochondritis
sternum
Costochondritis (kos-tō-kon-dr ı̄  ́t is; itis = inflammation) refers to
inflammation and irritation of the costochondral joints, resulting
in localized chest pain. Any costochondral joint may be affected,
although the joints for ribs 2–6 are those most commonly injured.
The cause of costochondritis is usually unknown, but some docu-
mented causes include repeated minor trauma to the chest wall
(e.g., from forceful repeated coughing during a respiratory infection
or overexertion during exercise) and bacterial or viral infection of
the joints themselves. Some backpackers who do not use a chest
(a) Synchondroses (contain hyaline cartilage) brace have experienced bouts of costochondritis.

The most common symptom of costochondritis is localized chest

Intervertebral disc
pain, typically following exertion or a respiratory infection. The
pain may be mistaken for that caused by a myocardial infarc-
tion (heart attack), and thus may cause needless anxiety for
the patient. Sitting, lying on the affected side, and increased
mental stress can exacerbate symptoms. Costochondritis is not a
medical emergency and may be treated with NSAIDs (nonsteroidal
anti-inflammatory drugs, such as aspirin). With proper rest and
treatment, symptoms typically disappear after several weeks.

Body of vertebra Pubic symphysis

pelvis to change shape slightly as the fetus passes through the
(b) Symphyses (contain fibrocartilage) birth canal.
Other examples of symphyses are the intervertebral joints,
Figure 9.3 where the bodies of adjacent vertebrae are both separated and
Cartilaginous Joints. Articulating bones are joined by cartilage. united by intervertebral discs. These intervertebral discs allow
(a) Synchondroses are immobile joints that occur in an epiphyseal only slight movements between the adjacent vertebrae; however,
plate in a long bone and in the joint between a rib and the sternum. the collective movements of all the intervertebral discs afford the
(b) Symphyses are amphiarthroses and occur in the intervertebral spine considerable flexibility.
discs and the pubic symphysis.

W H AT D I D Y O U L E A R N?

cartilage) are united firmly to the manubrium of the sternum to ●

4 Describe a symphysis. In what functional category is this type of
joint placed, and why?
provide stability to the rib cage. A final example of synchondro-
ses are the costochondral (kos-tō-kon  ́dră l; costa = rib) joints, the
joints between each bony rib and its respective costal cartilage.
(Note that the costochondral joints are different from the articu-
9.4 Synovial Joints
lation between the sternum and the costal cartilage of ribs 2–7, Learning Objectives:
which is a synovial joint, not a synchondrosis.) 1. Describe the general anatomy of synovial joints and their
accessory structures.
W H AT D O Y O U T H I N K ? 2. Name the classes of synovial joints based on the joint
surface shapes, and identify the types of movement
●
1 Why is a synchondrosis a synarthrosis? Why would you want a
permitted.
synchondrosis to be immobile?
3. Discuss the variety of dynamic movements which occur at
9.3b Symphyses synovial joints.
A symphysis (sim  ́ fi-sis; pl., -sē z; growing together) has a pad of Synovial joints are freely mobile articulations. Unlike the
fibrocartilage between the articulating bones. The fibrocartilage joints previously discussed, the bones in a synovial joint are sepa-
resists compression and tension stresses and acts as a resilient rated by a space called a joint cavity. Most of the commonly known
shock absorber. All symphyses are amphiarthroses, meaning that joints in the body are synovial joints, including the glenohumeral
they allow slight mobility. (shoulder) joint, the temporomandibular joint, the elbow joint, and
One example of a symphysis is the pubic symphysis, which the knee joint. Functionally, all synovial joints are classified as
is located between the right and left pubic bones. In pregnant diarthroses, since all are freely mobile. Often, the terms diarthrosis
females, the pubic symphysis becomes more mobile to allow the and synovial joint are equated.

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 Chapter Nine Articulations 257

remove wastes to these cells. Whenever movement occurs at

a synovial joint, the combined compression and re-expansion
Periosteum of the articular cartilage circulate the synovial fluid into and
out of the cartilage matrix.
Yellow bone marrow
3. Synovial fluid acts as a shock absorber, distributing stresses
and force evenly across the articular surfaces when the
pressure in the joint suddenly increases.
All articulating bone surfaces in a synovial joint are cov-
Fibrous layer ered by a thin layer of hyaline cartilage called articular cartilage.
Articular
Synovial
capsule
This cartilage reduces friction in the joint during movement, acts
membrane as a spongy cushion to absorb compression placed on the joint,
Joint cavity and prevents damage to the articulating ends of the bones. This
(containing synovial fluid) special hyaline cartilage lacks a perichondrium. Mature cartilage
Articular cartilage is avascular, so it does not have blood vessels to bring nutrients
Ligament to and remove waste products from the tissue. The repetitious
compression/relaxation that occurs during exercise is vital to the
articular cartilage’s well-being because the accompanying pump-
ing action enhances its nutrition and waste removal.
Ligaments (lig  ́ă-ment; ligamentum = a band) are composed
of dense regular connective tissue. Ligaments connect one bone
to another bone and strengthen and reinforce most synovial
joints. Extrinsic ligaments are outside of and physically separate
from the articular capsule, whereas intrinsic ligaments represent
thickenings of the articular capsule itself. Intrinsic ligaments
Typical synovial joint include extracapsular ligaments outside the articular capsule and
intracapsular ligaments within the articular capsule.
Figure 9.4
Tendons (ten  ́dŏn; tendo = extend) are not part of the syno-
Synovial Joints. All synovial joints are diarthroses, and they
vial joint itself. Like a ligament, a tendon is composed of dense
permit a wide range of motion.
regular connective tissue. However, whereas a ligament binds
bone to bone, a tendon attaches a muscle to a bone. When a
muscle contracts, the tendon from that muscle moves the bone to
9.4a General Anatomy of Synovial Joints which it is attached, thus creating movement at the joint. Tendons
help stabilize joints because they pass across or around a joint
All types of synovial joints have several basic features: an articu-
providing mechanical support, and can limit the range or amount
lar capsule, a joint cavity, synovial fluid, articular cartilage, liga-
of movement permitted at a joint.
ments, and nerves and blood vessels (figure 9.4).
All synovial joints have numerous sensory nerves and blood
Each synovial joint is composed of a double-layered cap-
vessels that innervate and supply the articular capsule and associ-
sule called the articular (ar-tik  ́ū-lă r) capsule (or joint capsule).
ated ligaments. The sensory nerves detect painful stimuli in the
The outer layer is called the fibrous layer, while the inner layer
joint and report on the amount of movement and stretch in the
is a synovial membrane (or synovium). The fibrous layer is
joint. By monitoring stretching at a joint, the nervous system can
formed from dense connective tissue, and it strengthens the joint
detect changes in our posture and adjust body movements.
to prevent the bones from being pulled apart. The synovial mem-
In addition to the main structures just described, synovial
brane is composed primarily of areolar connective tissue, covers
joints usually have the following accessory structures: bursae, fat
all the internal joint surfaces not covered by cartilage, and lines
pads, and tendons.
the articular capsule.
A bursa (ber  ́să; pl., bursae, ber  ́sē; a purse) is a fibrous,
Only synovial joints house a joint cavity (or articular cavity),
saclike structure that contains synovial fluid and is lined by a
a space that contains a small amount of synovial fluid. The cavity
synovial membrane (figure 9.5a). Bursae are found around
permits separation of the articulating bones. The articular cartilage
most synovial joints and also where bones, ligaments, muscles,
and synovial fluid within the joint cavity reduce friction as bones
skin, or tendons overlie each other and rub together. Bursae may
move at a synovial joint.
be either connected to the joint cavity or completely separate
Lining the joint cavity is the synovial membrane, which
from it. They are designed to alleviate the friction resulting from
secretes a viscous, oily synovial fluid. Synovial fluid is composed
the various body movements, such as a tendon or ligament rub-
of secretions from synovial membrane cells and a filtrate from
bing against bone. An elongated bursa called a tendon sheath
blood plasma. Synovial fluid has three functions:
wraps around tendons where there may be excessive friction.
1. Synovial fluid lubricates the articular cartilage on the Tendon sheaths are especially common in the confined spaces of
articulating bones (in the same way that oil in a car engine the wrist and ankle (figure 9.5b).
lubricates the moving engine parts). Fat pads are often distributed along the periphery of a syno-
2. Synovial fluid nourishes the articular cartilage’s vial joint. They act as packing material and provide some protec-
chondrocytes. The relatively small volume of synovial fluid tion for the joint. Often fat pads fill the spaces that form when
must be circulated continually to provide nutrients and bones move and the joint cavity changes shape.

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 258 Chapter Nine Articulations

Tendon sheath
(opened)

Tendon of flexor
digitorum profundus

Tendon of flexor
digitorum superficialis
Femur
Suprapatellar bursa Digital tendon
Bursa deep to Synovial membrane sheaths
gastrocnemius
muscle
Patella
Articular capsule
Prepatellar
Articular cartilage
bursa
Meniscus
Fat pad
Tendon sheath
Joint cavity filled
Infrapatellar around flexor
with synovial fluid
bursae pollicis longus Common flexor
tendon tendon sheath
Tibia Patellar ligament

Tendon of flexor
carpi radialis Tendons of flexor
digitorum superficialis
Tendon of flexor and flexor digitorum
pollicis longus profundus

(a) Bursae of the knee joint, sagittal section (b) Tendon sheaths of wrist and hand, anterior view

Figure 9.5
Bursae and Tendon Sheaths. Synovial-fluid-filled structures called bursae and tendon sheaths reduce friction where ligaments, muscles,
tendons, and bones rub together. (a) The knee joint contains a number of bursae. (b) The wrist and hand contain numerous tendon sheaths (blue).

■ A joint is biaxial (bı̄-ak  ́sē-ă l; bi = double) if the bone moves

CLINICAL VIEW in two planes or axes.
■ A joint is multiaxial (or triaxial [trı̄-ak  ́sē-ăl; tri = three]) if
“Cracking Knuckles” the bone moves in multiple planes or axes.

Cracking or popping sounds often result when people pull forcefully

Note that all synovial joints are diarthroses, although some
on their fingers. Stretching or pulling on a synovial joint causes the
are more mobile than others. From least mobile to most freely
joint volume to immediately expand and the pressure on the fluid
mobile, the six specific types of synovial joints are plane joints,
within the joint to decrease, so that a partial vacuum exists within
hinge joints, pivot joints, condylar joints, saddle joints, and ball-
the joint. As a result, the gases dissolved in the fluid become less
and-socket joints (figure 9.6).
soluble, and they form bubbles, a process called cavitation. When
A plane (planus = flat) joint, also called a planar or gliding
the joint is stretched to a certain point, the pressure in the joint
joint, is the simplest synovial articulation and the least mobile
drops even lower, so the bubbles in the fluid burst, producing a
type of diarthrosis. This type of synovial joint is also known as a
popping or cracking sound. (Similarly, displaced water in a sealed
uniaxial joint because only side-to-side movements are possible.
vacuum tube makes this sound as it hits against the glass wall.)
The articular surfaces of the bones are flat, or planar. Examples of
It typically takes about 25 to 30 minutes for the gases to dissolve
plane joints include the intercarpal and intertarsal joints (the joints
back into the synovial fluid. You cannot crack your knuckles again
between the cube-shaped carpal and tarsal bones).
until these gases dissolve. Contrary to popular belief, cracking your
A hinge joint is a uniaxial joint in which the convex surface of
knuckles does not cause arthritis.
one articulating bone fits into a concave depression on the other bone.
Movement is confined to a single axis, like the hinge of a door. An
example is the elbow joint. The trochlear notch of the ulna fits directly
9.4b Types of Synovial Joints into the trochlea of the humerus, so the forearm can be moved only
anteriorly toward the arm or posteriorly away from the arm. Other
Synovial joints are classified by the shapes of their articulating
hinge joints occur in the knee and the finger (interphalangeal [IP])
surfaces and the types of movement they allow. Movement of a
joints.
bone at a synovial joint is best described with respect to three
A pivot (piv ́ŏt) joint is a uniaxial joint in which one articulat-
intersecting perpendicular planes or axes:
ing bone with a rounded surface fits into a ring formed by a ligament
■ A joint is said to be uniaxial (yū-nē-ak  ́sē-ă l; unus = one) if and another bone. The first bone rotates on its longitudinal axis
the bone moves in just one plane or axis. relative to the second bone. An example is the proximal radioulnar

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 Chapter Nine Articulations 259

Dens of axis

Atlas

Axis

Pivot joint Ball-and-socket joint

Ilium

Hinge joint

Humerus

Radius

Head of femur

Ulna

Carpal bones

Plane joint Triquetrum

Hamate bone Trapezium

First Saddle joint

metacarpal
bone
Phalanges

Metacarpal bone
Proximal phalanx

Condylar joint

Figure 9.6
Types of Synovial Joints. These six types of synovial joints permit specific types of movement.

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 260 Chapter Nine Articulations

joint, where the rounded head of the radius pivots along the ulna (between the trapezium and the first metacarpal) is an example
and permits the radius to rotate. Another example is the atlantoaxial of a saddle joint. This joint permits the thumb to move toward the
joint between the first two cervical vertebrae. The rounded dens of other fingers so that we can grasp objects.
the axis fits snugly against an articular facet on the anterior arch of Ball-and-socket joints are multiaxial joints in which the
the atlas. This joint pivots when you shake your head “no.” spherical articulating head of one bone fits into the rounded, cup-
Condylar (kon  ́d i-lar) joints, also called condyloid or ellip- like socket of a second bone. Examples of these joints are the hip
soid joints, are biaxial joints with an oval, convex surface on joint and the glenohumeral joint. The multiaxial nature of these
one bone that articulates with a concave articular surface on the joints permits movement in three axes. Move your arm at your
second bone. Biaxial joints can move in two axes, such as back- shoulder, and observe the wide range of movements that can be
and-forth and side-to-side. Examples of condylar joints are the produced. This is why the ball-and-socket joint is considered the
metacarpophalangeal (MP) (met ắ -kar ṕ ō-fă-lan ́ jē-ă l) joints of most freely mobile type of synovial joint.
fingers 2 through 5. The MP joints are commonly referred to as
“knuckles.” Examine your hand and look at the movements along W H AT D O Y O U T H I N K ?
the MP joints; you can flex and extend the fingers at this joint
(that is one axis of movement). You also can move your fingers ●
2 If a ball-and-socket joint is more mobile than a plane joint, which
of these two joints is more stable?
apart from one another and move them closer together, which is
the second axis of movement.
A saddle joint is so named because the articular surfaces 9.4c Movements at Synovial Joints
of the bones have convex and concave regions that resemble the Four types of motion occur at synovial joints: gliding, angular,
shape of a saddle. It allows a greater range of movement than either rotational, and special movements (motions that occur only at
a condylar or hinge joint. The carpometacarpal joint of the thumb specific joints) (table 9.2).

Table 9.2 Movements at Synovial Joints

Movement Description Opposing Movement1
Gliding Motion Two opposing articular surfaces slide past each other in almost any direction; the amount of None
movement is slight
Angular Motion The angle between articulating bones increases or decreases
Flexion The angle between articulating bones decreases; usually occurs in the sagittal plane Extension
Extension The angle between articulating bones increases; usually occurs in the sagittal plane Flexion
Hyperextension Extension movement continues past the anatomic position Flexion
Lateral flexion The vertebral column moves in either lateral direction along a coronal plane None
Abduction Movement of a bone away from the midline; usually in the coronal plane Adduction
Adduction Movement of a bone toward the midline; usually in the coronal plane Abduction
Circumduction A continuous movement that combines flexion, abduction, extension, and adduction in None
succession; the distal end of the limb or digit moves in a circle
Rotational Motion A bone pivots around its own longitudinal axis None
Pronation Rotation of the forearm whereby the palm is turned posteriorly Supination
Supination Rotation of the forearm whereby the palm is turned anteriorly Pronation
Special Movements Types of movement that don’t fit in the previous categories
Depression Movement of a body part inferiorly Elevation
Elevation Movement of a body part superiorly Depression
Dorsiflexion Ankle joint movement whereby the dorsum of the foot is brought closer to the anterior Plantar flexion
surface of the leg
Plantar flexion Ankle joint movement whereby the sole of the foot is brought closer to the posterior surface Dorsiflexion
of the leg
Inversion Twisting motion of the foot that turns the sole medially or inward Eversion
Eversion Twisting motion of the foot that turns the sole laterally or outward Inversion
Protraction Anterior movement of a body part from anatomic position Retraction
Retraction Posterior movement of a body part from anatomic position Protraction
Opposition Special movement of the thumb across the palm toward the fingers to permit grasping and Reposition
holding of an object

1. Some movements (e.g., circumduction) do not have an opposing movement.

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 Chapter Nine Articulations 261

Extension

Flexion Hyperextension
Hyperextension

Flexion

Extension
Extension

Flexion

(a) (b) (c)

Lateral
flexion

Figure 9.7
Flexion, Extension, Hyperextension, and Lateral Flexion.
Flexion decreases the joint angle in an anterior-posterior (AP) plane,
Flexion while extension increases the joint angle in the AP plane. Lateral
flexion decreases a joint angle, but in a coronal plane. Examples
of joints that allow some of these movements are (a) the atlanto-
occipital joint, (b) the elbow joint, (c) the radiocarpal joint, (d) the
Extension knee joint, and (e) the intervertebral joints.
(d) (e)

Gliding Motion between the articulating bones. Extension is a straightening action

Gliding is a simple movement in which two opposing surfaces slide that usually occurs in the sagittal plane of the body. Straightening
slightly back-and-forth or side-to-side with respect to one another. your arm and forearm until the upper limb projects directly away
In a gliding motion, the angle between the bones does not change, from the anterior side of your body or straightening your fingers
and only limited movement is possible in any direction. Gliding after making a clenched fist are examples of extension. Flexion and
motion typically occurs along plane joints. extension of various body parts are illustrated in figure 9.7a–d.
Hyperextension (hı̄ ṕ er-eks-ten ś hŭn; hyper = above normal)
Angular Motion is the extension of a joint beyond 180 degrees. For example, if you
Angular motion either increases or decreases the angle between two extend your arm and hand with the palm facing inferiorly, and
bones. These movements may occur at many of the synovial joints; then raise the back of your hand as if admiring a new ring on your
they include the following specific types: flexion and extension, hyper- finger, the wrist is hyperextended. If you glance up at the ceiling
extension, lateral flexion, abduction and adduction, and circumduction. while standing, your neck is hyperextended.
Flexion (flek  ́shŭn; flecto = to bend) is movement in an Lateral flexion occurs when the trunk of the body moves in a
anterior-posterior (AP) plane of the body that decreases the angle coronal plane laterally away from the body. This type of movement
between the articulating bones. Bones are brought closer together occurs primarily between the vertebrae in the cervical and lumbar
as the angle between them decreases. Examples include bending regions of the vertebral column (figure 9.7e).
your fingers toward your palm to make a fist, bending your fore- Abduction (ab-dŭk  ́shŭn), which means to “move away,” is
arm toward your arm at the elbow, flexion at the shoulder when a lateral movement of a body part away from the body midline.
you raise an arm anteriorly, and flexion of the neck when you bend Abduction occurs when either the arm or the thigh is moved laterally
your head anteriorly to look down at your feet. The opposite of flex- away from the body midline. Abduction of either the fingers or
ion is extension (eks-ten  ́shŭn; extensio = a stretching out), which the toes means that you spread them apart, away from the longest
is movement in an anterior-posterior plane that increases the angle digit, which is acting as the midline. Abducting the wrist (also

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 262 Chapter Nine Articulations

Abduction

Adduction

Abduction

Adduction
Abduction Adduction
(a) (b) (c)

Abduction Adduction

Figure 9.8
Abduction and Adduction. Abduction moves a body part away
from the trunk in a lateral direction, while adduction moves the body
part toward the trunk. Some examples occur at (a) the glenohumeral
joint, (b) the radiocarpal joint, (c) the hip joint, and (d) the
metacarpophalangeal (MP) joints.

(d)

known as radial deviation) involves pointing the hand and fin- Rotational Motion
gers laterally, away from the body. The opposite of abduction is Rotation is a pivoting motion in which a bone turns on its own
adduction (ad-dŭk  ́shŭn), which means to “move toward,” and longitudinal axis (figure 9.10). Rotational movement occurs at
is the medial movement of a body part toward the body midline. the atlantoaxial joint, which pivots when you rotate your head to
Adduction occurs when you bring your raised arm or thigh back gesture “no.” Some limb rotations are described as either away
toward the body midline, or in the case of the digits, toward the from the median plane or toward it. For example, lateral rota-
midline of the hand. Adducting the wrist (also known as ulnar tion (or external rotation) turns the anterior surface of the femur
deviation) involves pointing the hand and fingers medially, toward or humerus laterally, while medial rotation (or internal rotation)
the body. Abduction and adduction of various body parts are turns the anterior surface of the femur or humerus medially.
shown in figure 9.8. Pronation (prō-nā ś hŭn) is the medial rotation of the forearm
Circumduction (ser-kŭm-dŭk  ́shŭn; circum = around, duco = to so that the palm of the hand is directed posteriorly or inferiorly.
draw) is a sequence of movements in which the proximal end of an The radius and ulna are crossed to form an X. Supination (soo ṕ i-
appendage remains relatively stationary while the distal end makes nā ś hŭn; supinus = supine) occurs when the forearm rotates later-
a circular motion (figure 9.9). The resulting movement makes an ally so that the palm faces anteriorly or superiorly, and the radius
imaginary cone shape. For example, when you draw a circle on is parallel with the ulna. In the anatomic position, the forearm is
the blackboard, your shoulder remains stationary while your hand supinated. Figure 9.10d illustrates pronation and supination.
moves. The tip of the imaginary cone is the stationary shoulder,
while the rounded “base” of the cone is the circle the hand makes.
Circumduction is a complex movement that occurs as a result of a Special Movements
continuous sequence of flexion, abduction, extension, and adduction. Some motions occur only at specific joints and do not readily fit
into any of the functional categories previously discussed. These
W H AT D O Y O U T H I N K ? special movements include depression and elevation, dorsiflexion
●
3 When sitting upright in a chair, are your hip and knee joints flexed and plantar flexion, inversion and eversion, protraction and retrac-
or extended? tion, and opposition.

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 Chapter Nine Articulations 263

Figure 9.9
Circumduction. Circumduction is a complex movement
that involves flexion, abduction, extension, and adduction in
succession. Examples of joints that allow this movement are (a) the
glenohumeral joint and (b) the hip joint.

Circumduction

Circumduction
(a) (b)

Lateral rotation Medial rotation

Rotation
(a) (b)

Lateral rotation Medial rotation

Pronation Supination
(c) (d)

Figure 9.10
Rotational Movements. Rotation allows a bone to pivot on its longitudinal axis. Examples of joints that allow this movement are (a) the
atlantoaxial joint, (b) the glenohumeral joint, and (c) the hip joint. (d) Pronation and supination occur at the forearm.

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 264 Chapter Nine Articulations

Depression Elevation

Dorsiflexion

Plantar
flexion

(a) (b)

Opposition of
thumb and little finger

Protraction

Inversion Eversion

Retraction
(c) (d) (e)

Figure 9.11
Special Movements Allowed at Synovial Joints. (a) Depression and elevation at the glenohumeral joint. (b) Dorsiflexion and plantar flexion at
the talocrural joint. (c) Inversion and eversion at the intertarsal joints. (d) Protraction and retraction at the temporomandibular joint. (e) Opposition
at the carpometacarpal joints.

Depression (de = away or down, presso = to press) is the inferior ground when you take a step. In plantar (plan  ́tă r; planta = sole of
movement of a part of the body. Examples of depression include foot) flexion, movement at the talocrural joint permits extension of
the movement of the mandible while opening your mouth to chew the foot so that the toes point inferiorly. When a ballerina is stand-
food and the movement of your shoulders in an inferior direction. ing on her tiptoes, her ankle joint is in full plantar flexion.
Elevation is the superior movement of a body part. Examples of Inversion and eversion are movements that occur at the
elevation include the superior movement of the mandible while intertarsal joints of the foot only (figure 9.11c). In inversion (in-
closing your mouth at the temporomandibular joint and the move- ver  ́zhŭn; turning inward), the sole of the foot turns medially. In
ment of the shoulders in a superior direction (shrugging your eversion (ē-ver  ́zhŭn; turning outward), the sole turns to face later-
shoulders). Figure 9.11a illustrates depression and elevation at ally. (Note: Some orthopedists and runners use the terms pronation
the glenohumeral joint. and supination when describing foot movements as well, instead of
Dorsiflexion and plantar flexion are limited to the ankle using inversion and eversion. Inversion is foot supination, whereas
joint (figure 9.11b). Dorsiflexion (dōr-si-flek ś hŭn) occurs when the eversion is foot pronation.)
talocrural (ankle) joint is bent such that the superior surface of the Protraction (prō-trak  ́shŭn; to draw forth) is the anterior
foot and toes moves toward the leg. This movement occurs when movement of a body part from anatomic position, as when moving
you dig in your heels, and it prevents your toes from scraping the your jaw anteriorly at the temporomandibular joint or hunching

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 Chapter Nine Articulations 265

your shoulders anteriorly by crossing your arms. In the latter case, In this section, we examine the structure and function of the
the clavicles move anteriorly due to movement at both the acromio- more commonly known articulations of the axial and appendicular
clavicular and sternoclavicular joints. Retraction (rū-trak  ́shŭn; to skeletons. For the axial skeleton, we present in-depth descriptions
draw back) is the posteriorly directed movement of a body part of the temporomandibular joint and the intervertebral articula-
from anatomic position. Figure 9.11d illustrates protraction and tions. Table 9.3 summarizes the main features of these two areas
retraction at the temporomandibular joint. and also provides comparable information about the other major
At the carpometacarpal joint, the thumb moves toward the joints of the axial skeleton.
palmar tips of the fingers as it crosses the palm of the hand. This
movement is called opposition (op  ́pō-si  ́shŭn) (figure 9.11e). It 9.5a Joints of the Axial Skeleton
enables the hand to grasp objects and is the most distinctive digital Temporomandibular Joint
movement in humans. The opposite movement is called reposition.
The temporomandibular (tem  ́pŏ-rō-man-dib  ́ū-lă r) joint (TMJ)
is the articulation formed at the point where the head of the
mandible articulates with the articular tubercle of the temporal
bone anteriorly and the mandibular fossa posteriorly. This small,
Study Tip! complex articulation is the only mobile joint between skull bones.
When your mother tells you to “pull your shoulders back and stand The temporomandibular joint has several unique anatomic fea-
up straight,” you are retracting your shoulders. Conversely, when you are tures (figure 9.12). A loose articular capsule surrounds the joint
slumped forward in a chair, your shoulders are protracted. and promotes an extensive range of motion. The TMJ is poorly
stabilized, and thus a forceful anterior or lateral movement of the
mandible can result in partial or complete dislocation of the man-
dible. The joint contains an articular disc, which is a thick pad
W H AT D I D Y O U L E A R N?
of fibrocartilage separating the articulating bones and extending
●
5 What are the basic characteristics of all types of synovial joints? horizontally to divide the joint cavity into two separate chambers.
●
6 Compare the structure and motion permitted in saddle and As a result, the temporomandibular joint is really two synovial
joints—one between the temporal bone and the articular disc, and
condylar joints.
a second between the articular disc and the mandible.
●
7 Describe the following types of movements, and give an example
Several ligaments support this joint. The sphenomandibular
of each: (a) flexion, (b) circumduction, and (c) opposition.
ligament (an extracapsular ligament) is a thin band that extends
anteriorly and inferiorly from the sphenoid to the medial surface of
9.5 Selected Articulations in Depth the mandibular ramus. The stylomandibular ligament (an extra-
capsular ligament) is a thick band that extends from the styloid
Learning Objective: process of the temporal bone to the mandibular angle. The tem-
1. Describe the characteristics of the major articulations of the poromandibular ligament (or lateral ligament) is composed of two
axial and appendicular skeletons. short bands on the lateral portion of the articular capsule. These

Temporomandibular
ligament Articular surface
of mandibular fossa
Articular capsule

External
acoustic meatus

Styloid process Articular disc

Stylomandibular ligament Articular capsule
Sphenomandibular ligament Articular tubercle
Head of mandible
Coronoid process of mandible

Styloid process

Figure 9.12
Temporomandibular Joint. The articulation between the head of the mandible and the mandibular fossa of the temporal bone exhibits a wide
range of movements.

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 266 Chapter Nine Articulations

Table 9.3 Axial Skeleton Joints

Joint Articulation Components Structural Classification

Suture Adjacent skull bones Fibrous joint

Suture Temporomandibular Head of mandible and mandibular Synovial (hinge, plane) joints
Temporomandibular fossa of temporal bone
Head of mandible and articular
Atlanto-occipital tubercle of temporal bone
Atlantoaxial
Atlanto-occipital Superior articular facets of atlas Synovial (condylar) joint
and occipital condyles of occipital
bone
Intervertebral

Atlantoaxial Anterior arch of atlas and dens Synovial (pivot) joint

of axis

Vertebrocostal
Intervertebral Vertebral bodies of adjacent Cartilaginous joint (symphysis)
vertebrae between vertebral bodies; synovial
Superior and inferior articular (plane) joint between articular
processes of adjacent processes
vertebrae
Lumbosacral
Vertebrocostal Facets of heads of ribs and bodies Synovial (plane) joint
of adjacent thoracic vertebrae
and intervertebral discs between
adjacent vertebrae
Articular part of tubercles of ribs
and facets of transverse processes
of thoracic vertebrae

Lumbosacral Body of the fifth lumbar vertebra Cartilaginous joint (symphysis)

Sternocostal and base of the sacrum between lumbar body and base of
Inferior articular facets of fifth sacrum; synovial (plane) joint between
lumbar vertebra and superior articular facets
articular facets of first sacral
vertebra

Sternocostal Sternum and first seven pairs Cartilaginous joint (synchondrosis)

of ribs between sternum and first ribs;
synovial (plane) joint between sternum
and ribs 2–7

bands extend inferiorly and posteriorly from the articular tubercle The anulus fibrosus contains collagen fibers that attach the disc to
to the mandible. the bodies of adjacent vertebrae. The anulus fibrosus also shares
The temporomandibular joint exhibits hinge, gliding, and connections with many of the ligaments that run along the bodies
some pivot joint movements. It functions like a hinge during jaw of the vertebrae. The nucleus pulposus is the inner gelatinous core
depression and elevation while chewing. It glides slightly forward of the disc and is primarily composed of water, with some scat-
during protraction of the jaw for biting, and glides slightly from side- tered reticular and elastic fibers.
to-side to grind food between the teeth during chewing. Two factors compress the substance of the nucleus pulposus
and displace it in every direction—movement of the vertebral col-
Intervertebral Articulations umn and the weight of the body. However, as humans age, water
Intervertebral articulations occur between the bodies of the ver- is gradually lost from the nucleus pulposus within each disc. Thus,
tebrae, as well as between the superior and inferior articular pro- over time the discs become less effective as a cushion, and the
cesses of adjacent vertebrae. All of the vertebral bodies, between chances for vertebral injury increase. Loss of water by the discs
the axis (C2) and the sacrum, are separated and cushioned by pads also contributes to the shortening of the vertebral column, which
of fibrocartilage called intervertebral discs (figure 9.13). Each accounts for the characteristic decrease in height that occurs with
intervertebral disc consists of two components: (1) an anulus fibro- advanced age.
sus and (2) a nucleus pulposus. The anulus fibrosus is the tough Several ligaments stabilize the vertebral column by support-
outer layer of fibrocartilage that covers each intervertebral disc. ing vertebrae through attachments to either their bodies or their

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 Chapter Nine Articulations 267

CLINICAL VIEW
Functional Classification Description of Movement

Synarthrosis None allowed TMJ Disorders

The temporomandibular joint (TMJ) is subject to various disor-
Diarthrosis Depression, elevation, lateral
displacement, protraction, retraction, ders. The most common TMJ disorder occurs as a result of alterna-
slight rotation tions in the ligaments that secure the joint, causing progressive
internal displacement of the articular disc. As the articular disc
is forced out of its normal position, a clicking or popping noise
Diarthrosis Extension and flexion of the head; may be heard as the person opens or closes the mouth. Other
slight lateral flexion of head to sides
symptoms may include headaches and sinus pressure as well as
pain in such areas as the paranasal sinuses, tympanic membrane,
Diarthrosis Head rotation oral cavity, eyes, and teeth. The widespread distribution of pain
is due to the fact that all of these structures, including the
muscle and jaw, are innervated by numerous sensory fibers of
Amphiarthrosis between Extension, flexion, lateral flexion of the trigeminal nerve.
vertebral bodies; diarthrosis vertebral column
between articular processes TMJ disorders are often seen in people who habitually chew gum
or grind or clench their teeth. Patients are advised to avoid
activities that cause jaw fatigue and to follow a soft diet. The
physician may also prescribe a bite appliance for the patient to
Diarthrosis Some slight gliding
wear at night to prevent grinding and clenching of the teeth.
Surgery can correct structural TMJ disorders, but is usually used
only as a last resort.

Amphiarthrosis between body Extension, flexion, lateral flexion of Anulus

and base; diarthrosis between vertebral column fibrosus
Intervertebral
articular facets Nucleus
disc
pulposus
Facet of
superior articular
process
Posterior
Synarthrosis between sternum No movement between sternum and longitudinal
and first ribs; diarthrosis between first ribs; some gliding movement ligament
sternum and ribs 2–7 permitted between sternum and ribs
2–7
Inferior articular process
Superior articular process

Interspinous
ligament
processes. The anterior longitudinal ligament is a thick, sturdy
ligament that attaches vertebral bodies and intervertebral discs
at their anterior surfaces. The posterior longitudinal ligament Supraspinous
attaches the posterior aspects of the vertebral bodies and discs. It is ligament
much thinner than the anterior longitudinal ligament, and it runs
within the vertebral canal. Multiple interspinous ligaments inter- Ligamentum Anterior longitudinal
connect the spinous processes of adjacent vertebrae. Their angled flavum ligament
fibers merge with the supraspinous ligament. The supraspinous
ligament interconnects the tips of the spinous processes from C7
to the sacrum. The ligamentum (lig  ́ă-men  ́tŭm) nuchae (noo  ́kē;
back of neck) is the part of the supraspinous ligament that extends
between C7 and the base of the skull. The ligamentum nuchae is
very thick and sturdy, and helps stabilize the skull on the cervical
vertebrae. The ligamentum flavum (flā  ́vŭm) connects the lami- Figure 9.13
nae of adjacent vertebrae. Intervertebral Articulations. Vertebrae articulate with adjacent
A second type of intervertebral articulation occurs at the vertebrae at both their superior and inferior articular processes.
synovial joints between adjacent superior and inferior articular Intervertebral discs separate the bodies of adjacent vertebrae.

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 268 Chapter Nine Articulations

Table 9.4 Pectoral Girdle and Upper Limb Joints

Joint Articulation Components

Sternoclavicular Sternal end of clavicle, manubrium of sternum, and first

Sternoclavicular
costal cartilage

Acromioclavicular Acromioclavicular Acromial end of clavicle and acromion of

scapula
Glenohumeral Glenohumeral Glenoid cavity of scapula and head of humerus

Humeroulnar Trochlea of humerus and trochlear notch

of ulna
Humeroradial Capitulum of humerus and head
of radius
Radioulnar Proximal joint: Head of radius and radial notch
of ulna
Distal joint: Distal end of ulna and ulnar notch
of radius
Humeroulnar
Radiocarpal Distal end of radius; lunate, scaphoid, and
Humeroradial triquetrum

Radioulnar (proximal)
Intercarpal Adjacent bones in proximal row
of carpal bones
Adjacent bones in distal row of
carpal bones
Adjacent bones between proximal and distal rows
Radiocarpal (midcarpal joints)
Radioulnar (distal) Carpometacarpal Thumb: Trapezium (carpal bone) and first metacarpal
Intercarpal Other digits: Carpals and metacarpals II–V
Carpometacarpal of digit 1 (thumb)
Carpometacarpal of digits 2–5
Metacarpophalangeal (MP Head of metacarpals and bases of proximal phalanges
joints, “knuckles”)
Metacarpophalangeal (MP)

Interphalangeal (IP joints) Heads of proximal and middle phalanges with bases of
Interphalangeal (IP) middle and distal phalanges, respectively

processes. The articular facets of the superior and inferior articular Sternoclavicular Joint
processes form plane joints that permit restricted gliding move- The sternoclavicular (ster  ́nō -kla-vik  ́ū-lă r) joint is a saddle
ments. An articular capsule surrounds these articular processes. joint formed by the articulation between the manubrium of the
The movement possible between a single set of vertebrae is sternum and the sternal end of the clavicle (figure 9.14). An
limited. However, when you add the movements of all the inter- articular disc partitions the sternoclavicular joint into two parts
vertebral joints of all the vertebrae together, an entire range of and creates two separate joint cavities. As a result, a wide range
movements becomes possible, including flexion, extension, lateral of movements is possible, including elevation, depression, and
flexion, and some rotation. circumduction.
Support and stability are provided to this articulation by
W H AT D O Y O U T H I N K ? the fibers of the articular capsule. The anterior sternoclavicular
ligament and the posterior sternoclavicular ligament reinforce
●
4 In which position does the anterior longitudinal ligament become
the capsule. In addition, two extracapsular ligaments also help
taut: flexion or extension?
strengthen the joint: (1) The clavicle is attached to the first rib
by the strong, wide costoclavicular ligament. This ligament sta-
9.5b Joints of the Pectoral Girdle and Upper Limbs bilizes the joint and prevents dislocation of the shoulder when
Table 9.4 lists the features of the major joints of the pectoral girdle the shoulder is elevated. (2) The interclavicular ligament runs
and upper limbs. Here, we provide an in-depth examination of along the sternal notch and attaches to each clavicle. It reinforces
several of these joints. the superior regions of the adjacent capsules. This design makes

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 Chapter Nine Articulations 269

Structural Functional Description of Movement

Classification Classification
Synovial (saddle) Diarthrosis Elevation, depression,
circumduction
Synovial (plane) Diarthrosis Gliding of scapula on clavicle Anterior Interclavicular
sternoclavicular ligament Clavicle
ligament
Synovial (ball- Diarthrosis Abduction, adduction,
and-socket) circumduction, extension, flexion,
hyperextension, lateral rotation,
First rib Articular
and medial rotation of arm
disc
Synovial (hinge) Diarthrosis Extension and flexion of forearm Costoclavicular Articular capsule
ligament
Manubrium of sternum
Synovial (hinge) Diarthrosis Extension and flexion of forearm

Synovial (pivot) Diarthrosis Rotation of radius with respect to

Second rib Costal cartilage Body of sternum
the ulna
Anterior view

Posterior Interclavicular
Synovial Diarthrosis Abduction, adduction, sternoclavicular ligament Clavicle
(condylar) circumduction, extension, and ligament
flexion of wrist
Synovial (plane) Diarthrosis Gliding
First rib

Costoclavicular Manubrium of sternum

ligament
Synovial (saddle) Diarthrosis Abduction, adduction, Posterior view
at thumb; circumduction, extension, flexion,
synovial (plane) and opposition at thumb; gliding Figure 9.14
at other digits at other digits Sternoclavicular Joint. The sternoclavicular joint helps stabilize
Synovial Diarthrosis Abduction, adduction, movements of the entire shoulder.
(condylar) circumduction, extension, and
flexion of phalanges
Synovial (hinge) Diarthrosis Extension and flexion of torn (as occurs in severe shoulder separations; see Clinical View),
phalanges
the acromion and clavicle no longer align properly.

Glenohumeral (Shoulder) Joint

The glenohumeral (glē  ́nō-hū  ́mer-ăl) joint is commonly referred
to as the shoulder joint. It is a ball-and-socket joint formed by the
articulation of the head of the humerus and the glenoid cavity of
the sternoclavicular joint very stable. If a person falls on an out- the scapula (figure 9.15). It permits the greatest range of motion of
stretched hand so that force is applied to the joint, the clavicle will any joint in the body, and so it is also the most unstable joint in
fracture before this joint ever dislocates. the body and the one most frequently dislocated.
The fibrocartilaginous glenoid labrum encircles and covers
Acromioclavicular Joint the surface of the glenoid cavity. A relatively loose articular capsule
The acromioclavicular (ă-krō  ́mē-ō-kla-vik  ́ū-lă r) joint is a plane attaches to the surgical neck of the humerus. The glenohumeral
joint between the acromion and the acromial end of the clavicle joint has several major ligaments. The coracoacromial (kōr ́ă-kō-ă-
(figure 9.15). A fibrocartilaginous articular disc lies within the krō ́mē-ăl) ligament extends across the space between the coracoid
joint cavity between these two bones. This joint works with both process and the acromion. The large coracohumeral (kōr ́ă-kō-
the sternoclavicular joint and the glenohumeral joint to give the hū ́mer-ăl) ligament is a thickening of the superior part of the joint
upper limb a full range of movement. capsule. It runs from the coracoid process to the humeral head. The
Several ligaments provide great stability to this joint. The glenohumeral ligaments are three thickenings of the anterior por-
articular capsule is strengthened superiorly by an acromioclavicu- tion of the articular capsule. These ligaments are often indistinct or
lar ligament. In addition, a very strong coracoclavicular (kōr  ́ă- absent and provide only minimal support. The transverse humeral
kō-kla-vik  ́ū-lă r) ligament binds the clavicle to the coracoid process ligament is a narrow sheet that extends between the greater and
of the scapula. The coracoclavicular ligament is responsible for lesser tubercles of the humerus. In addition, the tendon of the long
most of the stability of the joint, because it indirectly prevents the head of biceps brachii travels within the articular capsule and helps
clavicle from losing contact with the acromion. If this ligament is stabilize the humeral head in the joint.

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 270 Chapter Nine Articulations

Acromioclavicular ligament Clavicle

Acromion Coracoclavicular ligament

Subacromial bursa Coracoacromial ligament

Coracohumeral ligament Coracoid process

Subcoracoid bursa
Subdeltoid
bursa Glenohumeral ligaments

Transverse humeral ligament

Tendon sheath

Tendon of long head

of biceps brachii

Humerus

Acromioclavicular ligament Clavicle

Acromion Coracoclavicular ligament

Coracohumeral ligament Coracoacromial ligament

Tendon sheath Coracoid process

Glenohumeral ligaments (cut)

Tendon of long head

of biceps brachii

Humerus

(a) Right shoulder region, anterior view

Figure 9.15
Acromioclavicular and Glenohumeral Joints. (a) Anterior diagrammatic view and cadaver photo of both joints on the right side of the body.
(b) Right lateral view and (c) right coronal section show the articulating bones and supporting structures at the shoulder.

Ligaments of the glenohumeral joint strengthen the joint only joint lacks rotator cuff muscles, this area is weak and is the most
minimally. Most of the joint’s strength is due to the rotator cuff likely site of injury.
muscles surrounding it. The rotator cuff muscles (supraspinatus, Bursae help decrease friction at the specific places on the
infraspinatus, teres minor, and subscapularis) work as a group to shoulder where both tendons and large muscles extend across
hold the head of the humerus in the glenoid cavity. The tendons of the articular capsule. The shoulder has a relatively large number
these muscles encircle the joint (except for the inferior portion) and of bursae. The subacromial (sŭb-ă-krō  ́mē-ăl) bursa prevents
fuse with the articular capsule. Because the inferior portion of the rubbing between the acromion and the articular capsule. The

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 Chapter Nine Articulations 271

Tendon of long head Coracoacromial ligament Acromion Acromioclavicular joint

of biceps brachii
Clavicle Clavicle
Acromioclavicular tendon
Coracoclavicular Articular disc
Supraspinatus tendon ligaments
Tendon of long head Supraspinatus
Coracoid process
Acromion tendon
of biceps brachii
Infraspinatus Subcoracoid
tendon bursa Subdeltoid bursa Synovial
membrane
Subacromial bursa Subscapularis Deltoid muscle
muscle Glenoid cavity
Teres minor muscle
of scapula
Glenoid cavity Subscapular bursa
Glenoid labrum Glenohumeral
Articular capsule ligaments Glenoid labrum
Humerus
Articular
capsule

(b) Right lateral view (c) Right coronal section

CLINICAL VIEW

■ Pain when the arm is abducted more than 90 degrees, the

Shoulder Separation
position at which significant movement occurs between the
The term shoulder separation refers to a dislocation of the acromiocla- separated clavicular and acromial surfaces
vicular joint. Dislocation (dis-lō-kā  ́shŭn; dis = apart, locatio = placing)
Acromioclavicular dislocations are graded according to severity. In
is a joint injury in which the articulating bones have separated. This
the most severe injury, the joint is completely dislocated, and the
injury often results from a hard blow to the joint, as when a hockey
coracoclavicular ligament is torn. Since the coracoclavicular ligament
player is “slammed into the boards.” Shoulder separation is also com-
provides most of the stability to this joint, damage to it means the
mon in wrestlers. The symptoms of a shoulder separation include:
bones will not stay in alignment. The coracoclavicular ligament must
■ Tenderness and edema (swelling) in the area of the joint be surgically repaired in order for the bones of the joint to remain
■ Surface deformity at the acromioclavicular joint; since the bones fixed in place.
are displaced, the acromion is very prominent and appears more
pointed.

subcoracoid bursa prevents contact between the coracoid pro- stability and mobility in a joint. Thus, while the elbow joint is
cess and the articular capsule. The subdeltoid bursa and the very stable, it is not as mobile as some other joints, such as the
subscapular bursa allow for easier movements of the deltoid and glenohumeral joint.
supraspinatus muscles, respectively. The elbow joint has two main supporting ligaments. The
radial collateral ligament (or lateral collateral ligament) is
Elbow Joint responsible for stabilizing the joint at its lateral surface; it extends
The elbow joint is a hinge joint composed primarily of two articu- around the head of the radius between the anular ligament and
lations: (1) the humeroulnar joint, where the trochlear notch of the lateral epicondyle of the humerus. The ulnar collateral liga-
the ulna articulates with the trochlea of the humerus; and (2) the ment (or medial collateral ligament) stabilizes the medial side of
humeroradial joint, where the capitulum of the humerus articu- the joint and extends from the medial epicondyle of the humerus
lates with the head of the radius. These joints are enclosed within to the coronoid process of the ulna, and posteriorly to the olec-
a single articular capsule (figure 9.16). ranon. In addition, an anular (an  ́ū-lă r; anulus = ring) ligament
The elbow is an extremely stable joint for several reasons. surrounds the neck of the radius and binds the proximal head of
First, the articular capsule is fairly thick, and thus effectively pro- the radius to the ulna. The anular ligament helps hold the head
tects the articulations. Second, the bony surfaces of the humerus of the radius in place, allowing for rotation of the radial head
and ulna interlock very well, and thus provide a solid bony sup- against the ulna for pronation and supination of the forearm.
port. Finally, multiple strong supporting ligaments help reinforce Despite the support from the capsule and ligaments, the
the articular capsule. Remember that there is a tradeoff between elbow joint is subject to damage from a severe impact or unusual

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 272 Chapter Nine Articulations

CLINICAL VIEW

Dislocation of the 2. The head of the humerus tears the inferior part of the capsule
and dislocates the humerus, so that the humerus lies inferior to
Glenohumeral Joint the glenoid cavity.
Because the glenohumeral joint is very mobile and yet unstable, dis- 3. Once the humeral head has become dislocated from the glenoid
locations are very common. Glenohumeral dislocations usually occur cavity, the anterior thorax (chest) muscles pull on the head
when a fully abducted humerus is struck hard—for example, when a superiorly and medially, causing the humeral head to lie just
quarterback is hit as he is about to release a football, or when a person inferior to the coracoid process.
falls on an outstretched hand.
The result is that the shoulder appears flattened and “squared-off,”
The following sequence of events occurs in a glenohumeral dislocation: because the humeral head is dislocated anteriorly and inferiorly to the
glenohumeral joint capsule.
1. Immediately after the initial blow, the head of the humerus pushes
into the inferior part of the articular capsule. (Recall the inferior Some glenohumeral dislocations can be repaired by “popping” the
part of the capsule is relatively weak and not protected by muscle humerus back into the glenoid cavity. More severe dislocations may
tendons as the other surfaces of the capsule are.) need surgical repair.

Clavicle

Glenoid
Dislocated head “Squared-off” cavity
of humerus shoulder

Displaced head
of humerus

(a) Dislocated glenohumeral joint (b) Radiograph of a glenohumeral dislocation

stress. For example, if you fall on an outstretched hand with the radius, and a fibrocartilaginous articular disc (figure 9.17).
your elbow joint partially flexed, the posterior stress on the This articular disc separates the ulna from the radiocarpal joint
ulna combined with contractions of muscles that extend the (which is why the ulna is not considered part of this joint). The
elbow may break the ulna at the center of the trochlear notch. entire wrist complex is ensheathed by an articular capsule that
Sometimes dislocations result from stresses to the elbow. This is has reinforcing broad ligaments to support and stabilize the car-
particularly true when growth is still occurring at the epiphyseal pal bone positions. The radiocarpal joint is a condylar articula-
plate, so children and teenagers may be prone to humeral epicon- tion that permits flexion, extension, adduction, abduction, and
dyle dislocations or fractures. circumduction, but no rotation. Rotational movements (in the
form of supination and pronation) occur at the distal and proxi-
Radiocarpal (Wrist) Joint mal radioulnar joints.
The radiocarpal (rā  ́dē-ō-kar  ́păl) joint, also known as the wrist Additional movements in the carpus region are made pos-
joint, is an articulation among the three proximal carpal bones sible by intercarpal articulations, which are plane joints that
(scaphoid, lunate, and triquetrum), the distal articular surface of permit gliding movements between the individual carpal bones.

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 Chapter Nine Articulations 273

Humerus

Medial
Lateral epicondyle epicondyle Humerus

Articular capsule Articular Anular Tendon of biceps

Ulnar collateral capsule ligament brachii (cut)
Radial collateral ligament
ligament
Lateral
epicondyle
Anular ligament
Radius
Radius

Radial
Tendon of biceps Ulna collateral Ulna
brachii (cut) ligament

(a) Right elbow, anterior view (b) Right elbow, lateral view

Humerus Trochlea

Tendon of Anular Articular capsule

biceps brachii ligament Articular Humerus
(cut) capsule
Radius Coronoid process
Ulnar
collateral Radius
ligament

Articular
cartilage
Ulna
Olecranon

Ulna
(c) Right elbow, medial view (d) Right elbow, sagittal section

Figure 9.16
Elbow Joint. The elbow joint is a hinge joint. The right elbow is shown here in (a) anterior view, (b) lateral view, (c) medial view, and
(d) sagittal section.

W H AT D I D Y O U L E A R N?
●
10 Which structures are the primary stabilizers of the
●8 Describe the structural arrangement and function of the glenohumeral joint?
anulus fibrosus and the nucleus pulposus in an
intervertebral disc.
●
11 What is the function of the anular ligament in the
elbow joint?
●
9 Which ligaments limit the relative mobility of the
clavicle at the sternal end? At the acromial end?

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 274 Chapter Nine Articulations

Figure 9.17 Distal radioulnar joint

Radiocarpal joint
Radiocarpal Joint. A right
coronal section depicts the Articular disc
condylar articulation between Ulnar collateral ligament
Radial collateral ligament
the radius and three proximal Lunate
carpal bones. Scaphoid
Intercarpal joints Triquetrum

Carpometacarpal
joint of thumb

Right radiocarpal joint, coronal section

CLINICAL VIEW

Subluxation of the Radial Head A classic example of subluxation of the radial head occurs when a
parent or caregiver suddenly pulls on a child’s pronated forearm, and
The term subluxation refers to an incomplete dislocation, in which the the child, resisting, puts his or her upper limb in a flexed and partially
contact between the bony joint surfaces is altered, but they are still pronated position. As the child resists moving and the adult pulls on the
in partial contact. In subluxation of the head of the radius, the head upper limb, the head of the radius pulls out of the anular ligament. The
is pulled out of the anular ligament. Laymen’s terms for this injury child later complains of pain on the lateral side of the elbow, where a
include “pulled elbow,” “nursemaid’s elbow,” or “slipped elbow.” This prominent “bump” (caused by the subluxated radial head) also appears.
injury occurs commonly and almost exclusively in children (typically Luckily, treatment is simple: The pediatrician applies posteriorly placed
those younger than age 5), because a child’s anular ligament is thin pressure to the head of the radius while slowly supinating and extending
and the head of the radius is not fully formed. Thus, it is much easier the child’s forearm. This movement literally “screws” the radial head
for the head of the radius to be pulled out of the anular ligament. After back into the anular ligament. In most cases, this manual treatment
age 5, both the ligament and the radial head are more fully formed, brings immediate relief. A child who has had this injury may be more
and the risk of this type of injury lessens dramatically. likely to reinjure this articulation prior to age 5.

9.5c Joints of the Pelvic Girdle and Lower Limbs that of the glenohumeral joint. Conversely, the hip joint’s increased
Table 9.5 lists the features of the major joints of the pelvic girdle stability means that it is less mobile than the glenohumeral joint.
and lower limbs. Here, we provide an in-depth examination of The hip joint must be more stable (and thus less mobile) because it
several of these joints. supports the body weight.
The hip joint is secured by a strong articular capsule, several
Hip (Coxal) Joint ligaments, and a number of powerful muscles. The articular capsule
The hip joint, also called the coxal joint, is the articulation between extends from the acetabulum to the trochanters of the femur, enclos-
the head of the femur and the relatively deep, concave acetabulum ing both the femoral head and neck. This arrangement prevents the
of the os coxae (figure 9.18). A fibrocartilaginous acetabular head from moving away from the acetabulum. The ligamentous
labrum further deepens this socket. The hip joint’s more extensive fibers of the articular capsule reflect around the neck of the femur.
bony architecture is therefore much stronger and more stable than These reflected fibers, called retinacular (ret-i-nak  ́ū-lă r; retinacula =

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 Chapter Nine Articulations 275

Iliofemoral ligament
Ischiofemoral ligament
Iliofemoral
ligament Greater
Greater trochanter
trochanter

Pubofemoral
ligament

Lesser
Lesser trochanter
trochanter

Ischial tuberosity

(a) Right hip joint, anterior view (b) Right hip joint, posterior view

Acetabular labrum
Acetabulum
Articular capsule

Greater trochanter Acetabular labrum

Ligament of
of femur head of femur Ligament of
head of femur
Head of femur

Retinacular
fibers

Ischium

Articular capsule (cut)

(c) Right hip joint, coronal section (d) Right hip joint, anterior view, internal aspect of joint

Figure 9.18
Hip Joint. The hip joint is formed by the head of the femur and the acetabulum of the os coxae. The right hip joint is shown in (a) anterior view,
(b) posterior view, and (c) coronal section. (d) Cadaver photo of the hip joint, with the articular capsule cut to show internal structures.

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 276 Chapter Nine Articulations

Table 9.5 Pelvic Girdle and Lower Limb Joints

Joint Articulation Components Structural Classification

Sacroiliac Auricular surfaces of sacrum and ilia Synovial (plane)

Sacroiliac
Hip (coxal) Head of femur and acetabulum of Synovial (ball-and-socket)
os coxae
Hip

Pubic symphysis Pubic symphysis Two pubic bones Cartilaginous (symphysis)

Knee Patellofemoral joint: Patella and Both synovial (acts as hinge)

patellar surface of femur and synovial (plane) at
Tibiofemoral joint: Condyles of patellofemoral joint;
femur and condyles of tibia synovial (acts as hinge) at
tibiofemoral joint1
Tibiofibular Superior joint: Head of fibula and Superior joint:
lateral condyle of tibia Synovial (plane)
Patellofemoral (knee) Inferior joint: Distal end of fibula Inferior joint: Fibrous
and fibular notch of tibia (syndesmosis)
Tibiofemoral (knee)
Talocrural Distal end of tibia and medial Synovial (hinge)
Tibiofibular (superior) malleolus with talus
Lateral malleolus of fibula
and talus
Intertarsal Between the tarsal bones Synovial (plane)

Tarsometatarsal Three cuneiforms (tarsal bones), Synovial (plane)

cuboid, and bases of five metatarsal
bones

Tibiofibular (inferior)
Metatarsophalangeal Heads of metatarsals and bases of Synovial (condylar)
Talocrural (MP joints) proximal phalanges
Intertarsal
Tarsometatarsal
Interphalangeal (IP joints) Heads of proximal and middle Synovial (hinge)
Metatarsophalangeal (MP) phalanges with bases of
Interphalangeal (IP) middle and distal phalanges,
respectively

1. Although anatomists classify the tibiofemoral joint as a hinge joint, some kinesiologists and exercise scientists prefer to classify the tibiofemoral joint as a modified condylar joint.

a band) fibers, provide additional stability to the capsule. Traveling are taut, you don’t have as much mobility in the joint as you did
through the retinacular fibers are retinacular arteries (branches of when the hip joint was flexed.
the deep femoral artery), which supply almost all of the blood to the Another tiny ligament, the ligament of head of femur, also
head and neck of the femur. called the ligamentum teres, originates along the acetabulum. Its
The articular capsule is reinforced by three spiraling intra- attachment point is the center of the head of the femur. This liga-
capsular ligaments. The iliofemoral (il  ́ē-ō-fem  ́ŏ-ră l) ligament ment does not provide much strength to the joint; rather, it typi-
is a Y-shaped ligament that provides strong reinforcement for cally contains a small artery that supplies the head of the femur.
the anterior region of the articular capsule. The ischiofemoral The combination of a deep bony socket, a strong articu-
(is-kē-ō-fem  ́ō-răl) ligament is a spiral-shaped, posteriorly located lar capsule, supporting ligaments, and muscular padding gives
ligament. The pubofemoral (pū  ́ bō-fem  ́ŏ-ră l) ligament is a tri- the hip joint its stability. Movements possible at the hip joint
angular thickening of the capsule’s inferior region. All of these include flexion, extension, abduction, adduction, rotation, and
spiraling ligaments become taut when the hip joint is extended, circumduction.
so the hip joint is most stable in the extended position. Try this
experiment: Flex your hip joint, and try to move the femur; you Knee Joint
may notice a great deal of mobility. Now extend your hip joint The knee joint is the largest and most complex diarthrosis of the
(stand up), and try to move the femur. Because those ligaments body (figure 9.19). It primarily functions as a hinge joint, but

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 Chapter Nine Articulations 277

CLINICAL VIEW
Functional Description of
Classification Movement
Fracture of the Femoral Neck
Diarthrosis Slight gliding; more movement
during pregnancy and Fracture of the femoral neck is a common and complex injury.
childbirth
Although this injury is often referred to as a “fractured hip,” the
os coxae isn’t broken, just the femoral neck. When the femoral
Diarthrosis Abduction, adduction,
circumduction, extension, neck breaks, the pull of the lower limb muscles causes the leg to
flexion, medial and lateral rotate laterally and shorten by several inches. Fractures of the
rotation of thigh femoral neck are of two types: intertrochanteric and subcapital.
Amphiarthrosis Very slight movements;
Intertrochanteric fractures of the femoral neck occur distally
more movement during
childbirth to or outside the hip articular capsule—in other words, these
fractures are extracapsular. The fracture line runs between the
Diarthrosis Extension, flexion, lateral rotation greater and lesser trochanters. This type of injury typically occurs
of leg in flexed position, slight in younger and middle-aged individuals, and usually in response
medial rotation to trauma.

Subcapital fractures (or intracapsular fractures) of the femoral

Amphiarthrosis Slight rotation of fibula during neck occur within the hip articular capsule, very close to the
dorsiflexion of foot head of the femur itself. This type of fracture usually occurs in
elderly people whose bones have been weakened by osteoporosis.

Diarthrosis Dorsiflexion and plantar flexion

Subcapital fractures result in tearing of the retinacular fibers and
the retinacular arteries that supply the head and neck of the femur.
The ligament to the head of the femur may be torn as well. As a
result, the head and neck of the femur lose their blood supply. If a
Diarthrosis Eversion and inversion bone doesn’t have an adequate blood supply, it develops avascular
of foot necrosis, which is death of the bone tissue due to lack of blood.
Diarthrosis Slight gliding Avascular necrosis of the femoral head and neck is a common
complication in subcapital fractures. Frequently, hip replacement
surgery is needed, whereby a metal femoral head and neck replace
the dying bone. This surgery is not without risk, and many elderly
Diarthrosis Abduction, adduction, patients do not survive.
circumduction, extension,
and flexion of proximal
phalanges

Diarthrosis Extension and flexion of phalanges

the  joint. The fibular collateral ligament (lateral collateral liga-
ment) reinforces the lateral surface of the joint. This ligament
runs from the femur to the fibula and prevents hyperadduction of
the leg at the knee. (In other words, it prevents the leg from mov-
ing too far medially relative to the thigh.) The tibial collateral
ligament (medial collateral ligament) reinforces the medial sur-
face of the knee joint. This ligament runs from the femur to the
tibia and prevents hyperabduction of the leg at the knee. (In other
words, it prevents the leg from moving too far laterally relative to
when the knee is flexed, it is also capable of slight rotation and the thigh.) This ligament is attached to the medial meniscus of
lateral gliding. Structurally, the knee is composed of two sepa- the knee joint as well, so an injury to the tibial collateral ligament
rate articulations: (1) the tibiofemoral (tib-ē-ō-fem  ́ō-ră l) joint is usually affects the medial meniscus.
between the condyles of the femur and the condyles of the tibia, Deep to the articular capsule and within the knee joint
and (2) the patellofemoral joint is between the patella and the itself are a pair of C-shaped fibrocartilage pads located on the
patellar surface of the femur. condyles of the tibia. These pads, called the medial meniscus
The knee joint has an articular capsule that encloses only the and the lateral meniscus, partially stabilize the joint medially
medial, lateral, and posterior regions of the knee joint. The articular and laterally, act as cushions between articular surfaces, and
capsule does not cover the anterior surface of the knee joint; rather, continuously change shape to conform to the articulating sur-
the quadriceps femoris muscle tendon passes over the anterior sur- faces as the femur moves.
face. The patella is embedded within this tendon, and the patellar Also deep to the articular capsule of the knee joint are two
ligament extends beyond the patella and continues to its attach- cruciate (kroo  ́shē-āt) ligaments, which limit the anterior and
ment on the tibial tuberosity of the tibia. Thus, there is no single posterior movement of the femur on the tibia. These ligaments
unified capsule in the knee, nor is there a common joint cavity. cross each other in the form of an X, hence the name “cruciate”
On either side of the joint are two collateral ligaments that (which means “cross”). The anterior cruciate ligament (ACL)
become taut on extension and provide additional stability to runs from the posterior femur to the anterior side of the tibia.

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 278 Chapter Nine Articulations

Femur

Suprapatellar
bursa
Quadriceps femoris
muscle (cut)

Quadriceps femoris tendon

Fibular collateral
ligament Tibial collateral
ligament
Patella hidden within
quadriceps tendon

Patellar ligament

Fibula Tibia
Figure 9.19
Knee Joint. This joint is
the largest and most complex
(a) Right knee, anterior superficial view
diarthrosis of the body. (a)
Anterior superficial, (b) sagittal
section, (c) anterior deep, and
(d) posterior deep views reveal the
complex interrelationships among
the parts of the right knee. Femur

Quadriceps femoris tendon

Suprapatellar bursa

Articular capsule
Patella
Prepatellar bursa
Menisci
Infrapatellar fat pad
Anterior cruciate Patellar ligament
ligament
Infrapatellar bursae

Tibial tuberosity

Tibia

(b) Right knee, sagittal section

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 Chapter Nine Articulations 279

Articular cartilage

Posterior cruciate
ligament

Lateral condyle Lateral condyle

Medial condyle Medial condyle

Lateral meniscus
Lateral meniscus
Medial meniscus Medial meniscus

Fibular collateral Fibular collateral

ligament ligament
Anterior cruciate
ligament
Tibial collateral Tibial collateral
ligament ligament

Fibula Tibia Fibula Tibia

(c) Right knee, anterior deep view

Femur Femur

Anterior cruciate
ligament
Lateral condyle Lateral condyle
Medial condyle Medial condyle
Fibular collateral Fibular collateral
ligament ligament
Medial meniscus Lateral meniscus Lateral meniscus
Medial meniscus
Posterior cruciate
ligament

Tibial collateral Tibial collateral

ligament ligament
Tibia Fibula Tibia Fibula

(d) Right knee, posterior deep view

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 280 Chapter Nine Articulations

When the knee is extended, the ACL is pulled tight and prevents sion, the tibia rotates laterally so as to tighten the anterior cruciate
hyperextension. The ACL prevents the tibia from moving too ligament and squeeze the meniscus between the tibia and femur.
far anteriorly on the femur. The posterior cruciate ligament Muscular contraction by the popliteus muscle unlocks the knee
(PCL) runs from the anteroinferior femur to the posterior side joint. Contraction of this muscle causes a slight rotational movement
of the tibia. The PCL becomes taut on flexion, and so it prevents between the tibia and the femur.
hyperflexion of the knee joint. The PCL also prevents posterior
displacement of the tibia on the femur. Talocrural (Ankle) Joint The talocrural joint, or ankle joint, is
a highly modified hinge joint that permits dorsiflexion and plan-
“Locking” the Knee Humans are bipedal animals, meaning that tar flexion, and includes two articulations within one articular
they walk on two feet. An important aspect of bipedal locomotion capsule. One of these articulations is between the distal end of
is the ability to “lock” the knees in the extended position and stand the tibia and the talus, and the other is between the distal end of
erect for long periods without tiring the leg muscles. At full exten- the fibula and the lateral aspect of the talus (figure 9.20). The

CLINICAL VIEW: In Depth

Knee Ligament Injuries when a player is illegally “clipped” by a lateral blow to the knee, and
the leg is forcibly abducted and laterally rotated. If the blow is severe
Although the knee is capable of bearing much weight and has numer- enough, the tibial collateral ligament tears, followed by tearing of the
ous strong supporting ligaments, it is highly vulnerable to injury, medial meniscus, because these two structures are connected. The
especially among athletes. The knee is susceptible to both horizontal force that tears the tibial collateral ligament and the medial meniscus
and rotational stress, most commonly when struck either from the is thus transferred to the ACL. Because the ACL is relatively weak, it
lateral or posterior aspect while slightly flexed. Because the knee is tears as well.
reinforced by tendons and ligaments only, ligamentous injuries to the
The treatment of ligamentous knee injuries depends upon the sever-
knee are very common.
ity and type of injury. Conservative treatment involves immobilizing
The tibial collateral ligament is frequently injured when the leg is the knee for a period of time to rest the joint. Surgical treatment can
forcibly abducted at the knee. For example, if a person’s knee is hit include repairing the torn ligaments or replacing the ligaments with a
on the lateral side, the leg is hyperabducted, and the tibial collateral graft from another tendon or ligament (such as the quadriceps tendon).
ligament is strained and frequently torn. Because the tibial collateral Rehabilitation of the knee also requires strengthening the muscles
ligament is attached to the medial meniscus, the medial meniscus and tendons that surround the knee, so they can provide additional
may be injured as well. support to the joint.
Injury to the fibular collateral ligament can occur if the medial side
of the knee is struck, resulting in hyperadduction of the leg at the
knee. This type of injury is fairly rare, in part because the fibular col-
lateral ligament is very strong and also because medial blows to the
knee are not common.

The anterior cruciate ligament (ACL) can be injured when the leg is
hyperextended—for example, if a runner’s foot hits a hole. Because
the ACL is rather weak compared to the other knee ligaments, it is
especially prone to injury. ACL injury often occurs in association with
another ligament injury. To test for ACL injury, a physician gently tugs
anteriorly on the tibia when the knee is flexed and not bearing weight.
In this so-called “anterior drawer test,” too much forward movement Torn tibial
collateral
indicates an ACL tear. ligament
Lateral blow to knee
Posterior cruciate ligament (PCL) injury may occur if the leg is hyper- Torn medial
flexed or if the tibia is driven posteriorly on the femur. PCL injury occurs meniscus
rarely, because this ligament is rather strong. To test for PCL injury, a Torn anterior
physician gently pushes on the tibia while the knee is flexed and not cruciate ligament
bearing weight. In this “posterior drawer test,” too much posterior
movement indicates a PCL tear.

The unhappy triad of injuries refers to a triple ligamentous injury of

the tibial collateral ligament, medial meniscus, and anterior cruciate
ligament, and is the most common type of football injury. It occurs “Unhappy triad” of injuries to the right knee.

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 Chapter Nine Articulations 281

Fibula Tibia
Fibula Tibia

Anterior tibiofibular
ligament Talus

Talus
Lateral ligament Lateral ligament

Posterior
tibiofibular
ligament
Calcaneus

Calcaneus
Metatarsal V Metatarsal V

(a) Right foot, lateral view (b) Right foot, anterolateral view

Tibia Tibia
Deltoid ligament Deltoid ligament

Navicular bone
Talus Talus

Calcaneus Calcaneus

Metatarsal I Metatarsal I Navicular bone

(c) Right foot, medial view

Figure 9.20
Talocrural Joint. (a) Lateral, (b) anterolateral, and (c) medial views of the right foot show that the talocrural joint contains articulations among
the tibia, fibula, and talus. This joint permits dorsiflexion and plantar flexion only.

medial and lateral malleoli of the tibia and fibula, respectively, tibiofibular (tib-ē-ō-fib  ́ū-lă r) ligaments (anterior and poste-
form extensive medial and lateral margins and prevent the talus rior) bind the tibia to the fibula.
from sliding side-to-side.
The talocrural joint includes several distinctive anatomic Joints of the Foot
features. An articular capsule covers the distal surfaces of the Four types of synovial joints are found in the foot: intertarsal joints,
tibia, the medial malleolus, the lateral malleolus, and the talus. A tarsometatarsal joints, metatarsophalangeal joints, and interpha-
multipart deltoid ligament (or medial ligament) binds the tibia to langeal joints (figure 9.21). Intertarsal joints are the articulations
the foot on the medial side. This ligament prevents overeversion between the tarsal bones. Some of these joints go by specific names
of the foot. The deltoid ligament is incredibly strong and rarely (e.g., talonavicular joint, calcaneocuboid joint). It is at the intertar-
tears; in fact, it will pull the medial malleolus off the tibia sal joints that inversion and eversion of the foot occur.
before it ever ruptures! A much thinner, multipart lateral liga- The articulations between the tarsal and metatarsal bones
ment binds the fibula to the foot on the lateral side. This liga- form the tarsometatarsal (tar-sō-met  ́ă-tar  ́săl) joints. These are
ment prevents overinversion of the foot. It is not as strong as plane articulations that permit some twisting and limited side-to-
the deltoid ligament, and is prone to sprains and tears. Two side movements. The medial, intermediate, and lateral cuneiform

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 282 Chapter Nine Articulations

CLINICAL VIEW

Interphalangeal Ankle Sprains and Pott Fracture

(IP) joints
A sprain is a stretching or tearing of ligaments, without fracture
or dislocation of the joint. An ankle sprain results when the
foot is twisted, almost always due to overinversion. Fibers of
the lateral ligaments are either stretched (in mild sprains) or
torn (in more severe sprains), producing localized swelling and
tenderness anteroinferior to the lateral malleolus. Overeversion
sprains rarely occur due to the strength of the deltoid ligament.
Metatarsophalangeal
(MP) joints Remember from chapter 4 that ligaments are composed of dense
regular connective tissue, which is poorly vascularized. Tissue
that is poorly vascularized takes a long time to heal, and that
is the case with ankle sprains. They are also prone to reinjury.
I II
III If overeversion does occur, the injury that usually results is called
IV a Pott fracture (see chapter 6). If the foot is overeverted, it
V pulls on the deltoid ligament, which is very strong and doesn’t
tear. Instead, the pull on the deltoid ligament can avulse (pull
off) the medial malleolus of the tibia. The force from the injury
Tarsometatarsal joints then continues to move the talus laterally, because the medial
malleolus can no longer restrict side-to-side movements of the
ankle. As the talus moves laterally and puts force on the fibula,
Cuneiform bones the fibula fractures as well (usually at its distal end or by the
Intertarsal joints lateral malleolus). Thus, both the tibia and the fibula fracture in
this injury, and yet the deltoid ligament remains intact.
Navicular bone Cuboid
bone

W H AT D I D Y O U L E A R N?
Talus ●
12 Which ligaments support the hip joint?

●
13 List the intracapsular ligaments of the knee joint, and discuss their
function.

●
14 Compare the deltoid and lateral ligaments of the ankle joint.
Which of these ligaments is stronger? What types of injuries are
associated with these ligaments?
Calcaneus

9.6 Disease and Aging of the Joints

Right foot, superior view Learning Objective:
Figure 9.21 1. Identify the effects of aging on the joints.
Joints of the Foot. The intertarsal, tarsometatarsal, During a person’s lifetime, the joints are subjected to
metatarsophalangeal (MP), and interphalangeal (IP) joints help extensive wear and tear. A joint’s size, flexibility, and shape
move the toes and foot. are affected and modified by use. Active joints develop larger
and thicker capsules, and the supporting ligaments and bones
increase in size.
Prior to the closure of the epiphyseal plates in early adult-
bones articulate with the first three metatarsals. The fourth and hood, some injuries to a young person may result in sublux-
fifth metatarsals articulate with the cuboid. ation or fracture of an epiphysis, with potential adverse effects
The metatarsophalangeal (met  ́ă-tar  ́sō-fă-lan  ́ jē-ăl) joints, on the future development and health of the joint. After the
also called the MP joints, are between the metatarsals and the epiphyseal plates close, injuries at the epiphyses typically result
phalanges of the toes. These are condylar joints, and they permit in sprains.
limited abduction and adduction of the toes, as well as flexion and Arthritis is a disease that involves damage to articular carti-
extension. lage (see Clinical View: In Depth). A highly prevalent problem that
Finally, the interphalangeal (IP) joints occur between indi- develops in an aging joint is osteoarthritis, also known as degen-
vidual phalanges. Each interphalangeal joint is a hinge joint that erative arthritis. The cause of the damage may vary, but it can be
permits flexion and extension only. related to cumulative wear and tear at the joint surface.

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 Chapter Nine Articulations 283

CLINICAL VIEW: In Depth

Arthritis Rheumatoid arthritis starts with synovial membrane inflammation.
Fluid and white blood cells leak from small blood vessels into the
Arthritis (ar-thr ı̄  ́t is) is a group of inflammatory or degenerative joint cavity, causing an increase in synovial fluid volume. As a conse-
diseases of joints that occur in various forms. Each form presents the quence, the joint swells, and the inflamed synovial membrane thickens;
same symptoms: swelling of the joint, pain, and stiffness. It is the most eventually, the articular cartilage and, often, the underlying bone
prevalent crippling disease in the United States. Some common forms of become eroded. Scar tissue later forms and ossifies, and bone ends
arthritis are gouty arthritis, osteoarthritis, and rheumatoid arthritis. fuse together, immobilizing the joint. Medications that help suppress
the immune system (e.g., prednisone) are frequently used to alleviate
Gouty arthritis is typically seen in middle-aged and older individu-
the symptoms of rheumatoid arthritis.
als, and is more common in males. Often called “gout,” this disease
occurs as a result of an increased level of uric acid (a normal cel-
lular waste product) in the blood. This abnormal level causes urate
crystals to accumulate in the blood, synovial fluid, and synovial
membranes. The body’s inflammatory response to the urate crystals
results in joint pain. Gout usually begins with an attack on a single
joint (often in the great toe), and later progresses to other joints.
Eventually, gouty arthritis may immobilize joints by causing fusion
between the articular surfaces of the bones. Often, nonsteroidal
anti-inflammatory drugs (NSAIDs) are used to alleviate symptoms
and reduce the inflammation.

Osteoarthritis is the most common type of arthritis. This chronic

degenerative joint condition is termed “wear-and-tear arthritis”
because of its prevalence in weight-bearing joints and its association
with older adults. The entire joint is affected but the articular cartilage
appears to break down first. Eventually, bone rubs against bone, causing
abrasions on the bony surfaces, or eburnation. Without the protective
articular cartilage, movements at the joints become stiff and painful.
Weight-bearing joints most affected by osteoarthritis are those of the
hips, knees, feet, and cervical and lumbar regions of the spine. Other
(a) Hands with rheumatoid arthritis
joints commonly affected include the shoulders and interphalangeal
joints. Osteoarthritis is typically seen in older individuals, although
more and more athletes are experiencing arthritis at an earlier age
due to the repetitive stresses placed on their joints. NSAIDs are used
to alleviate the symptoms of osteoarthritis.

Rheumatoid (roo  ́mă-toyd) arthritis is typically seen in younger and

middle-aged adults, and is much more prevalent in women. It presents
with pain and swelling of the joints, muscle weakness, osteoporosis,
and assorted problems with both the heart and the blood vessels.

Rheumatoid arthritis is an autoimmune disorder in which the body’s

immune system targets its own tissues for attack. Although the cause of
this reaction is unknown, it often follows infection by certain bacteria
and viruses that have surface molecules similar to molecules normally
present in the joints. When the body’s immune system is stimulated
to attack the foreign molecules, it also destroys its own joint tissue,
thus initiating the autoimmune disorder. (b) Radiograph of hands with rheumatoid arthritis

Just as the strength of a bone is maintained by continual rate of degeneration of the articular cartilage is reduced. Exercise
application of stress, the health of joints is directly related to also strengthens the muscles that support and stabilize the joint.
moderate exercise. Exercise compresses the articular cartilages, However, extreme exercise should be avoided, because it aggra-
causing synovial fluid to be squeezed out of the cartilage and vates potential joint problems and may worsen osteoarthritis.
then pulled back inside the cartilage matrix. This flow of fluid Athletes such as baseball player Nolan Ryan and Olympic figure
gives the chondrocytes within the cartilage the nourishment skater Dorothy Hamill have experienced osteoarthritis at an early
required to maintain their health. Joints become stronger, and the age due to extreme exercise in their youth.

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 284 Chapter Nine Articulations

W H AT D I D Y O U L E A R N?
CLINICAL VIEW
●
15 Define osteoarthritis, and discuss what contributes to it.

Joint Replacement
Surgical joint replacement (arthroplasty) may be performed after
failure of other nonsurgical approaches. Before surgery is consid-
ered, treatment regimens include activity modification, use of
9.7 Development of the Joints
braces, exercise, medications such as nonsteroidal anti-inflam- Learning Objective:
matory drugs, and/or cortisone injections or viscosupplementation 1. Describe how joints develop in the embryo.
(e.g., hyaluronic acid injections) into the joint. Surgery involves Joints start to form by the sixth week of development and
removing the damaged cartilage and joint surface, modifying the become better differentiated during the fetal period. Some of
bone architecture to align the joint properly, and then a metal or the mesenchyme around the developing bones develops into the
plastic prosthetic is implanted to replace the joint surface. The connective tissues of the articulations. For example, in the area
options available, materials used, and recovery time are dependent of future fibrous joints, the mesenchyme around the developing
upon the joint being replaced. For instance, hip replacement usually bones differentiates into dense regular connective tissue, and later
includes complete replacement of the head and the neck of the joins the developing bones together. In cartilaginous joints, the
femur; and shoulder replacement includes the articular surfaces. mesenchyme differentiates into either fibrocartilage or hyaline
The recovery time for total knee replacement surgery is the short- cartilage.
est, between 6 and 8 weeks, with full recovery expected within The development of the synovial joints is more complex than
6 months. Total shoulder replacement incurs the longest recovery that of fibrous and cartilaginous joints (figure 9.22). The mesen-
time because the joint is immobilized between 6 and 8 weeks before chyme around the articulating bones differentiates into the com-
extensive physical therapy can begin. As materials and methods ponents of a synovial joint. The most laterally placed mesenchyme
advance, the longevity of the replaced joint has lengthened so that forms the articular capsule and supporting ligaments of the joint.
between 75% and 95% are still functional after 15 years. Just medial to this region, the mesenchyme forms the synovial
membrane, which then starts secreting synovial fluid into the joint

9 weeks

Cartilaginous
model of bone
Articular capsule
Developing Laterally located
joint cavity mesenchyme
Centrally located
mesenchyme

12 weeks

Bone

Epiphyseal plate
Articular
Epiphysis Menisci disc
Articular capsule Joint
Joint cavity cavities
Joint
Synovial cavity
membrane
Articular
cartilages

Free joint cavity Joint cavity with menisci Joint cavity with articular disc
(e.g., interphalangeal joint) (e.g., knee joint) (e.g., acromioclavicular joint)
Figure 9.22
Development of the Synovial Joints. By 9 weeks of development, as the future bones are developing, a primitive model of the synovial joint
cavities forms. Over the next several weeks, the synovial joints continue to differentiate. By 12 weeks, some have formed free joint cavities
(e.g., the interphalangeal joints) while others have formed menisci (e.g., the knee joint). Still other joints have an articular disc (e.g., the
acromioclavicular joint) that separates the articulating bones.

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 Chapter Nine Articulations 285

cavity. The centrally located mesenchyme differentiates in one of The articular disc assists the movement of the articulating
three ways, depending upon the type of synovial joint: bones. Examples of synovial joints with articular discs are
the sternoclavicular joint, the acromioclavicular joint, and
1. The centrally located mesenchyme is resorbed, and a free
the radiocarpal joint.
joint cavity forms. Examples of free joint cavities are the
interphalangeal joints of the fingers and toes. Differentiation of the centrally located mesenchyme occurs
2. The centrally located mesenchyme forms incomplete by about the twelfth week of development, and the entire joint
cartilaginous rings or blocks called menisci, which serve as continues to differentiate throughout the fetal period.
shock absorbers in joints. The knee joint is a synovial joint
that contains menisci.
W H AT D I D Y O U L E A R N?
3. The centrally located mesenchyme condenses and forms
a cartilaginous articular disc within the joint cavity. ●
16 Joints start to form during which week of development?

Clinical Terms

ankylosis (ang  ́ki-lō  ́sis) Stiffening of a joint due to the union of chondromalacia (kon  ́drō-mă-lā  ́shē-ă) patellae Softening of the
fibers or bones across the joint as the result of a disease. articular cartilage of the patella; sometimes considered a
arthralgia (ar-thral  ́jē-ă) Joint-associated pain that is not usually subtype of patellofemoral syndrome.
inflammatory. rheumatism (roo  ́mă-tizm) Any one of various conditions
arthroplasty (ar  ́thrō-plas-tē) Construction of an artificial joint exhibiting joint pain or other symptoms of articular origin;
to provide relief from or to correct advanced degenerative often associated with muscular or skeletal system problems.
arthritis. synovitis (sin-ō-vı̄  ́tis) Inflammation of the synovial membrane of
bursitis Inflammation of a bursa. a joint.

Chapter Summary
9.1 Articulations ■ Articulations occur where bones interact. Joints differ in structure, function, and the amount of movement they allow,
(Joints) 253 which may be extensive, slight, or none at all.
9.1a Classification of Joints 253
■ There are three structural categories of joints: fibrous, cartilaginous, and synovial.
■ The three functional categories of joints are synarthroses, which are immobile; amphiarthroses, which are slightly
mobile; and diarthroses, which are freely mobile.
9.2 Fibrous ■ In fibrous joints, articulating bones are interconnected by dense regular connective tissue.
Joints 254
9.2a Gomphoses 254
■ A gomphosis is a synarthrosis between the tooth and either the mandible or the maxillae.
9.2b Sutures 255
■ A suture is a synarthrosis that tightly binds bones of the skull. Closed sutures are called synostoses.
9.2c Syndesmoses 255
■ A syndesmosis is an amphiarthrosis, and the bones are connected by interosseous membranes.
9.3 Cartilaginous ■ In cartilaginous joints, articulating bones are attached to each other by cartilage.
Joints 255
9.3a Synchondroses 255
■ A synchondrosis is a synarthrosis where hyaline cartilage is wedged between articulating bones.
9.3b Symphyses 256
■ A symphysis is an amphiarthrosis, and has a disc of fibrocartilage wedged between the articulating bones.
9.4 Synovial ■ Synovial joints are diarthroses.
Joints 256
9.4a General Anatomy of Synovial Joints 257
■ Synovial joints contain an articular capsule, a joint cavity, synovial fluid, articular cartilage, ligaments, and nerves and
blood vessels.
9.4b Types of Synovial Joints 258
■ The six types of synovial joints are plane, hinge, pivot, condylar, saddle, and ball-and-socket.
9.4c Movements at Synovial Joints 260
■ Motions that occur at synovial joints include gliding, angular, rotational, and special.

(continued on next page)

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 286 Chapter Nine Articulations

Chapter Summary (continued)

9.5 Selected ■ In each articulation, unique features of the articulating bones support only the intended movement.
Articulations in
Depth 265 9.5a Joints of the Axial Skeleton 265
■ The temporomandibular joint is an articulation between the head of the mandible and the mandibular fossa of the
temporal bone.
■ Vertebrae articulate between their bodies as well as between the inferior and superior articular processes.
9.5b Joints of the Pectoral Girdle and Upper Limbs 268
■ The sternoclavicular joint is a saddle joint between the manubrium of the sternum and the sternal end of the
clavicle.
■ The acromioclavicular joint is a plane synovial joint between the acromion and the acromial end of the clavicle.
■ The glenohumeral joint is a ball-and-socket joint between the glenoid cavity of the scapula and the head of the
humerus.
■ The elbow is a hinge joint.
■ The radiocarpal joint involves the distal radius and three proximal carpal bones.
9.5c Joints of the Pelvic Girdle and Lower Limbs 274
■ The hip joint is a ball-and-socket joint between the head of the femur and the acetabulum of the os coxae.
■ The knee joint is primarily a hinge joint, but is capable of slight rotation and gliding.
■ The talocrural joint is a hinge joint that permits dorsiflexion and plantar flexion.
■ Intertarsal joints occur between the tarsal bones.
■ Tarsometatarsal joints are the articulations between the tarsal and metatarsal bones.
■ Metatarsophalangeal joints are the articulations between the metatarsals and the proximal phalanges.
■ Interphalangeal joints occur between individual phalanges.
9.6 Disease and ■ Osteoarthritis is a common joint problem that occurs with aging.
Aging of the
Joints 282
9.7 Development of ■ Joints begin to form during week 6 of development.
the Joints 284

Challenge Yourself
Matching Multiple Choice
Match each numbered item with the most closely related lettered Select the best answer from the four choices provided.
item.
______ 1. The greatest range of mobility of any joint in the
______ 1. joint between sternum a. talocrural joint body is found in the
and clavicle a. knee joint.
b. plantar flexion
______ 2. joint between tooth b. hip joint.
c. gomphosis c. glenohumeral joint.
and jaw
d. hip joint d. elbow joint.
______ 3. joint angle is increased
in an AP plane e. located in knee joint ______ 2. The movement of the foot that turns the sole
laterally is called
______ 4. bursa f. has anulus fibrosus and a. dorsiflexion.
nucleus pulposus b. inversion.
______ 5. palm faces posteriorly
g. pronation c. eversion.
______ 6. standing on tiptoe d. plantar flexion.
h. extension
______ 7. intervertebral disc ______ 3. A ________ is formed when two bones previously
i. sternoclavicular joint connected in a suture fuse.
______ 8. articulation among
tibia, fibula, and talus j. sac filled with synovial a. gomphosis
fluid b. synostosis
______ 9. menisci c. symphysis
______ 10. ligament of head d. syndesmosis
of femur

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 Chapter Nine Articulations 287

______ 4. The ligament that helps to maintain the alignment of Content Review
the condyles between the femur and tibia and to limit
the anterior movement of the tibia on the femur is the 1. Discuss the factors that influence both the stability and the
a. tibial collateral ligament. mobility of a joint. What is the relationship between a joint’s
b. posterior cruciate ligament. mobility and its stability?
c. anterior cruciate ligament. 2. Describe the structural differences between fibrous joints
d. fibular collateral ligament. and cartilaginous joints.

______ 5. The glenohumeral joint is primarily stabilized by the 3. Describe all joints that are functionally classified as
a. coracohumeral ligament. synarthroses.
b. glenohumeral ligaments. 4. Discuss the origin and function of synovial fluid within a
c. rotator cuff muscles that move the humerus. synovial joint.
d. scapula. 5. Compare a hinge joint and a pivot joint with respect to
______ 6. In a biaxial articulation, structure, function, and location within the body.
a. movement can occur in all three planes. 6. Describe and compare the movements of abduction,
b. only circumduction occurs. adduction, pronation, and supination.
c. movement can occur in two planes. 7. Describe the basic anatomy of the glenohumeral joint.
d. movement can occur in only one plane. 8. What are the main supporting ligaments of the elbow joint?
______ 7. A metacarpophalangeal (MP) joint, which has oval 9. How do the tibia and talus maintain their correct
articulating surfaces and permits movement in two positioning in the talocrural joint?
planes, is what type of synovial joint? 10. What is the primary age-related change that can occur in a
a. condylar joint?
b. plane
c. hinge Developing Critical Reasoning
d. saddle
1. During soccer practice, Erin tripped over the outstretched
______ 8. The ligament that is not associated with the leg of a teammate and fell directly onto her shoulder. She
intervertebral joints is the was taken to the hospital in excruciating pain. Examination
a. anterior longitudinal ligament. revealed that the head of the humerus had moved inferiorly
b. pubofemoral ligament. and anteriorly into the axilla. What happened to Erin in
c. ligamentum flavum. this injury?
d. supraspinous ligament. 2. While Lucas and Omar were watching a football game,
______ 9. Which of the following is a function of synovial fluid? a player was penalized for “clipping,” meaning that he
a. lubricates the joint had hit an opposing player on the lateral knee, causing
b. provides nutrients for articular cartilage hyperabduction at the knee joint. Lucas asked Omar what
c. absorbs shock within the joint the big deal was about “clipping.” What joint is most at
d. All of these are correct. risk, and what kind of injuries can occur if a player gets
“clipped”?
______ 10. All of the following movements are possible at the
radiocarpal joint except
a. circumduction.
b. abduction.
c. flexion.
d. rotation.

Answers to “What Do You Think?”

1. A synchondrosis is designed to be a synarthrosis because 2. The plane joint, the least mobile of the two joints, must be
as the bone ends are growing, they must not be allowed more stable than the ball-and-socket joint.
to move in relation to one another. For example, if the 3. When sitting upright in a chair, both the hip and knee
epiphysis and diaphysis move along the epiphyseal plate, joints are flexed.
bone growth is compromised and the bone becomes
4. The anterior longitudinal ligament becomes taut during
misshapen.
extension, so it is taut when we are standing and more
relaxed when we are sitting.

www.mhhe.com/mckinley3 Enhance your study with practice tests and activities to

assess your understanding. Your instructor may also recommend the interactive eBook,
individualized learning tools, and more.

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