9 JOINTS
JOINTS AND HOMEOSTASIS The joints of the skeletal system co
tribute to homeostasis by holding bones together in ways that allow for moveme
and flexibility. •
Bones are too rigid to bend without being damaged. Fortunate
flexible connective tissues form joints that hold bones together whi
still permitting, in most cases, some degree of movement. A join
also called an articulation (ar-tik-ū-LĀ-shun) or arthrosis (a
THRŌ-sis), is a point of contact between two bones, between bo
and cartilage, or between bone and teeth. When we say one bo
articulates with another bone, we mean that the bones form a join
You can appreciate the importance of joints if you have ever had
cast over your knee joint, which makes walking difficult, or
splint on your finger, which limits your ability to manipulate sma
objects. The scientific study of joints is termed arthrology (a
THROL-ō-jē; arthr- joint; logy study of). The study of m
tion of the human body is called kinesiology (ki-nē-sē-OL-ō-
kinesi movement).
264
, FIBROUS JOINTS
JOINT CLASSIFICATIONS The following sections present the joints of the
according to their structural classifications. As we ex
OBJECTIVE the structure of each type of joint, we will also outl
• Describe the structural and functional classifications of functions.
joints.
CHECKPOINT
Joints are classified structurally, based on their anatomical 1. On what basis are joints classified?
characteristics, and functionally, based on the type of movement
they permit.
The structural classification of joints is based on two criteria:
(1) the presence or absence of a space between the articulating
bones, called a synovial cavity, and (2) the type of connective FIBROUS JOINTS
tissue that binds the bones together. Structurally, joints are clas- OBJECTIVE
sified as one of the following types: • Describe the structure and functions of the three typ
fibrous joints.
• Fibrous joints (FĪ -brus): There is no synovial cavity, and
the bones are held together by dense irregular connective As previously noted, fibrous joints lack a synovial cavi
tissue that is rich in collagen fibers. the articulating bones are held very closely together by de
• Cartilaginous joints (kar-ti-LAJ-i-nus): There is no synovial regular connective tissue. Fibrous joints permit little or no
cavity and the bones are held together by cartilage. ment. The three types of fibrous joints are sutures, syndes
and interosseous membranes.
• Synovial joints (sı̄ -NŌ-vē-al): The bones forming the joint
have a synovial cavity and are united by the dense irregular
connective tissue of an articular capsule, and often by Sutures
accessory ligaments.
A suture (SOO-chur; sutur- seam) is a fibrous joint
The functional classification of joints relates to the degree of posed of a thin layer of dense irregular connective tissue; s
movement they permit. Functionally, joints are classified as one occur only between bones of the skull. An example is the
of the following types: nal suture between the parietal and frontal bones (Figure
The irregular, interlocking edges of sutures give them
• Synarthrosis (sin-ar-THRŌ-sis; syn- together): An im-
strength and decrease their chance of fracturing. Because a
movable joint. The plural is synarthroses.
is immovable, it is classified functionally as a synarthrosis
• Amphiarthrosis (am-fē-ar-THRŌ-sis; amphi- on both Some sutures that are present during childhood are re
sides): A slightly movable joint. The plural is amphi- by bone in the adult. Such a suture is an example of a syn
arthroses. (sin-os-TŌ-sis; os- bone), or bony joint—a joint in whic
• Diarthrosis (dı̄ -ar-THRŌ-sis movable joint): A freely is a complete fusion of two separate bones into one bon
movable joint. The plural is diarthroses. All diarthroses are example, the frontal bone grows in halves that join together
synovial joints. They have a variety of shapes and permit a suture line. Usually they are completely fused by age 6 a
several different types of movements. suture becomes obscure. If the suture persists beyond age
Figure 9.1 Fibrous joints.
At a fibrous joint the bones are held together by dense irregular connective tissue.
Inner compact bone
Spongy bone
Outer compact
bone
Coronal suture
(a) Suture between skull bones
FIGURE 9.1 CO N T
,266 CHAPTER 9 • JOINTS
F I G U R E 9 .1 CO N T I N U E D
Fibula
Socket of
alveolar
process
Tibia Root of
tooth
Anterior Periodontal
tibiofibular ligament
ligament
Syndesmosis between tibia and fibula Syndesmosis between tooth and socket
of alveolar process (gomphosis)
(b) Syndesmosis
Fibula
Interosseous
membrane
Tibia
(c) Interosseous membrane between tibia and fibula
? Functionally, why are sutures classified as synarthroses, and syndesmoses as amphiarthroses?
called a metopic suture (me-TŌ-pik; metopon forehead). A syn- maxillae and mandible (Figure 9.1b, right). The dense irregul
ostosis is also classified functionally as a synarthrosis. connective tissue between a tooth and its socket is the thin pe
odontal ligament (membrane). A gomphosis permits no moveme
(synarthrosis). Inflammation and degeneration of the gum
Syndesmoses periodontal ligament, and bone is called periodontal disease.
A syndesmosis (sin-dez-MŌ-sis; syndesmo- band or ligament)
is a fibrous joint in which there is a greater distance between the Interosseous Membranes
articulating surfaces and more dense irregular connective tissue
than in a suture. The dense irregular connective tissue is typically The final category of fibrous joint is the interosseous membran
arranged as a bundle (ligament) and the joint permits limited a substantial sheet of dense irregular connective tissue that bin
movement. One example of a syndesmosis is the distal tibiofibular neighboring long bones and permits slight movement (am
joint, where the anterior tibiofibular ligament connects the tibia phiarthrosis). There are two principal interosseous membra
and fibula (Figure 9.1b, left). It permits slight movement joints in the human body. One occurs between the radius a
(amphiarthrosis). Another example of a syndesmosis is called a ulna in the forearm (see Figure 8.6a, b on page 241) and t
gomphosis (gom-FŌ-sis; gompbo-bolt or nail) or dentoalveolar other occurs between the tibia and fibula in the leg (Figure 9.1c
joint, in which a cone-shaped peg fits into a socket. The only CHECKPOINT
examples of gomphoses in the human body are the articulations 2. Which fibrous joints are synarthroses? Which are
between the roots of the teeth and their sockets (alveoli) in the amphiarthroses?
, SYNOVIAL JOINTS
CARTILAGINOUS JOINTS immovable synostosis, or bony joint (see Figure 7.22b on
227).
OBJECTIVE
• Describe the structure and functions of the two types of Symphyses
cartilaginous joints.
A symphysis (SIM-fi-sis growing together) is a cartila
Like a fibrous joint, a cartilaginous joint lacks a synovial cavity joint in which the ends of the articulating bones are covere
and allows little or no movement. Here the articulating bones hyaline cartilage, but a broad, flat disc of fibrocartilage co
are tightly connected by either hyaline cartilage or fibrocartilage the bones. All symphyses occur in the midline of the bod
(see Table 4.4G, H on page 131). The two types of cartilaginous pubic symphysis between the anterior surfaces of the hip
joints are synchondroses and symphyses. is one example of a symphysis ( Figure 9.2b). This type o
is also found at the junction of the manubrium and body
Synchondroses sternum (see Figure 7.22) and at the intervertebral join
tween the bodies of vertebrae (see Figure 7.20a on page 2
A synchondrosis (sin-kon-DRŌ-sis; chondro- cartilage) is a portion of the intervertebral disc is compose
cartilaginous joint in which the connecting material is hyaline fibrocartilage. A symphysis is an amphiarthrosis, a s
cartilage. An example of a synchondrosis is the epiphyseal movable joint.
(growth) plate that connects the epiphysis and diaphysis of a
CHECKPOINT
growing bone (Figure 9.2a). A photomicrograph of the epiphy-
seal plate is shown in Figure 6.7a on page 185. Functionally, a 3. Which cartilaginous joints are synarthroses? Which a
synchondrosis is a synarthrosis. When bone elongation ceases, amphiarthroses?
bone replaces the hyaline cartilage, and the synchondrosis be-
comes a synostosis, a bony joint. Another example of a synchon-
drosis is the joint between the first rib and the manubrium of the SYNOVIAL JOINTS
sternum, which also ossifies during adult life and becomes an
OBJECTIVES
• Describe the structure of synovial joints.
Figure 9.2 Cartilaginous joints. • Describe the structure and function of bursae and te
At a cartilaginous joint the bones are held together sheaths.
by cartilage.
Structure of Synovial Joints
Epiphyseal (growth) Epiphysis Synovial joints (si-NŌ-vē-al) have certain characteristic
plates
distinguish them from other joints. The unique characterist
synovial joint is the presence of a space called a synovial (
Epiphysis cavity between the articulating bones (Figure 9.3). Becau
synovial cavity allows a joint to be freely movable, all sy
joints are classified functionally as diarthroses. The bone
synovial joint are covered by a layer of hyaline cartilage
articular cartilage. The cartilage covers the articulating s
Diaphysis of the bones with a smooth, slippery surface but does no
them together. Articular cartilage reduces friction between
(a) Synchondrosis in the joint during movement and helps to absorb shock.
Articular Capsule
Hip bones
A sleevelike articular (joint) capsule surrounds a synovia
encloses the synovial cavity, and unites the articulating
The articular capsule is composed of two layers, an outer fi
membrane and an inner synovial membrane (Figure 9.3
fibrous membrane usually consists of dense irregular conn
tissue (mostly collagen fibers) that attaches to the perioste
the articulating bones. In fact, the fibrous membrane is lite
Pubic
symphysis thickened continuation of the periosteum between the bone
flexibility of the fibrous membrane permits considerable
(b) Symphysis ment at a joint, while its great tensile strength (resista
stretching) helps prevent the bones from dislocating. The fi
? What is the structural difference between a synchondrosis some fibrous membranes are arranged as parallel bund
and a symphysis? dense regular connective tissue that are highly adapted for
JOINTS AND HOMEOSTASIS The joints of the skeletal system co
tribute to homeostasis by holding bones together in ways that allow for moveme
and flexibility. •
Bones are too rigid to bend without being damaged. Fortunate
flexible connective tissues form joints that hold bones together whi
still permitting, in most cases, some degree of movement. A join
also called an articulation (ar-tik-ū-LĀ-shun) or arthrosis (a
THRŌ-sis), is a point of contact between two bones, between bo
and cartilage, or between bone and teeth. When we say one bo
articulates with another bone, we mean that the bones form a join
You can appreciate the importance of joints if you have ever had
cast over your knee joint, which makes walking difficult, or
splint on your finger, which limits your ability to manipulate sma
objects. The scientific study of joints is termed arthrology (a
THROL-ō-jē; arthr- joint; logy study of). The study of m
tion of the human body is called kinesiology (ki-nē-sē-OL-ō-
kinesi movement).
264
, FIBROUS JOINTS
JOINT CLASSIFICATIONS The following sections present the joints of the
according to their structural classifications. As we ex
OBJECTIVE the structure of each type of joint, we will also outl
• Describe the structural and functional classifications of functions.
joints.
CHECKPOINT
Joints are classified structurally, based on their anatomical 1. On what basis are joints classified?
characteristics, and functionally, based on the type of movement
they permit.
The structural classification of joints is based on two criteria:
(1) the presence or absence of a space between the articulating
bones, called a synovial cavity, and (2) the type of connective FIBROUS JOINTS
tissue that binds the bones together. Structurally, joints are clas- OBJECTIVE
sified as one of the following types: • Describe the structure and functions of the three typ
fibrous joints.
• Fibrous joints (FĪ -brus): There is no synovial cavity, and
the bones are held together by dense irregular connective As previously noted, fibrous joints lack a synovial cavi
tissue that is rich in collagen fibers. the articulating bones are held very closely together by de
• Cartilaginous joints (kar-ti-LAJ-i-nus): There is no synovial regular connective tissue. Fibrous joints permit little or no
cavity and the bones are held together by cartilage. ment. The three types of fibrous joints are sutures, syndes
and interosseous membranes.
• Synovial joints (sı̄ -NŌ-vē-al): The bones forming the joint
have a synovial cavity and are united by the dense irregular
connective tissue of an articular capsule, and often by Sutures
accessory ligaments.
A suture (SOO-chur; sutur- seam) is a fibrous joint
The functional classification of joints relates to the degree of posed of a thin layer of dense irregular connective tissue; s
movement they permit. Functionally, joints are classified as one occur only between bones of the skull. An example is the
of the following types: nal suture between the parietal and frontal bones (Figure
The irregular, interlocking edges of sutures give them
• Synarthrosis (sin-ar-THRŌ-sis; syn- together): An im-
strength and decrease their chance of fracturing. Because a
movable joint. The plural is synarthroses.
is immovable, it is classified functionally as a synarthrosis
• Amphiarthrosis (am-fē-ar-THRŌ-sis; amphi- on both Some sutures that are present during childhood are re
sides): A slightly movable joint. The plural is amphi- by bone in the adult. Such a suture is an example of a syn
arthroses. (sin-os-TŌ-sis; os- bone), or bony joint—a joint in whic
• Diarthrosis (dı̄ -ar-THRŌ-sis movable joint): A freely is a complete fusion of two separate bones into one bon
movable joint. The plural is diarthroses. All diarthroses are example, the frontal bone grows in halves that join together
synovial joints. They have a variety of shapes and permit a suture line. Usually they are completely fused by age 6 a
several different types of movements. suture becomes obscure. If the suture persists beyond age
Figure 9.1 Fibrous joints.
At a fibrous joint the bones are held together by dense irregular connective tissue.
Inner compact bone
Spongy bone
Outer compact
bone
Coronal suture
(a) Suture between skull bones
FIGURE 9.1 CO N T
,266 CHAPTER 9 • JOINTS
F I G U R E 9 .1 CO N T I N U E D
Fibula
Socket of
alveolar
process
Tibia Root of
tooth
Anterior Periodontal
tibiofibular ligament
ligament
Syndesmosis between tibia and fibula Syndesmosis between tooth and socket
of alveolar process (gomphosis)
(b) Syndesmosis
Fibula
Interosseous
membrane
Tibia
(c) Interosseous membrane between tibia and fibula
? Functionally, why are sutures classified as synarthroses, and syndesmoses as amphiarthroses?
called a metopic suture (me-TŌ-pik; metopon forehead). A syn- maxillae and mandible (Figure 9.1b, right). The dense irregul
ostosis is also classified functionally as a synarthrosis. connective tissue between a tooth and its socket is the thin pe
odontal ligament (membrane). A gomphosis permits no moveme
(synarthrosis). Inflammation and degeneration of the gum
Syndesmoses periodontal ligament, and bone is called periodontal disease.
A syndesmosis (sin-dez-MŌ-sis; syndesmo- band or ligament)
is a fibrous joint in which there is a greater distance between the Interosseous Membranes
articulating surfaces and more dense irregular connective tissue
than in a suture. The dense irregular connective tissue is typically The final category of fibrous joint is the interosseous membran
arranged as a bundle (ligament) and the joint permits limited a substantial sheet of dense irregular connective tissue that bin
movement. One example of a syndesmosis is the distal tibiofibular neighboring long bones and permits slight movement (am
joint, where the anterior tibiofibular ligament connects the tibia phiarthrosis). There are two principal interosseous membra
and fibula (Figure 9.1b, left). It permits slight movement joints in the human body. One occurs between the radius a
(amphiarthrosis). Another example of a syndesmosis is called a ulna in the forearm (see Figure 8.6a, b on page 241) and t
gomphosis (gom-FŌ-sis; gompbo-bolt or nail) or dentoalveolar other occurs between the tibia and fibula in the leg (Figure 9.1c
joint, in which a cone-shaped peg fits into a socket. The only CHECKPOINT
examples of gomphoses in the human body are the articulations 2. Which fibrous joints are synarthroses? Which are
between the roots of the teeth and their sockets (alveoli) in the amphiarthroses?
, SYNOVIAL JOINTS
CARTILAGINOUS JOINTS immovable synostosis, or bony joint (see Figure 7.22b on
227).
OBJECTIVE
• Describe the structure and functions of the two types of Symphyses
cartilaginous joints.
A symphysis (SIM-fi-sis growing together) is a cartila
Like a fibrous joint, a cartilaginous joint lacks a synovial cavity joint in which the ends of the articulating bones are covere
and allows little or no movement. Here the articulating bones hyaline cartilage, but a broad, flat disc of fibrocartilage co
are tightly connected by either hyaline cartilage or fibrocartilage the bones. All symphyses occur in the midline of the bod
(see Table 4.4G, H on page 131). The two types of cartilaginous pubic symphysis between the anterior surfaces of the hip
joints are synchondroses and symphyses. is one example of a symphysis ( Figure 9.2b). This type o
is also found at the junction of the manubrium and body
Synchondroses sternum (see Figure 7.22) and at the intervertebral join
tween the bodies of vertebrae (see Figure 7.20a on page 2
A synchondrosis (sin-kon-DRŌ-sis; chondro- cartilage) is a portion of the intervertebral disc is compose
cartilaginous joint in which the connecting material is hyaline fibrocartilage. A symphysis is an amphiarthrosis, a s
cartilage. An example of a synchondrosis is the epiphyseal movable joint.
(growth) plate that connects the epiphysis and diaphysis of a
CHECKPOINT
growing bone (Figure 9.2a). A photomicrograph of the epiphy-
seal plate is shown in Figure 6.7a on page 185. Functionally, a 3. Which cartilaginous joints are synarthroses? Which a
synchondrosis is a synarthrosis. When bone elongation ceases, amphiarthroses?
bone replaces the hyaline cartilage, and the synchondrosis be-
comes a synostosis, a bony joint. Another example of a synchon-
drosis is the joint between the first rib and the manubrium of the SYNOVIAL JOINTS
sternum, which also ossifies during adult life and becomes an
OBJECTIVES
• Describe the structure of synovial joints.
Figure 9.2 Cartilaginous joints. • Describe the structure and function of bursae and te
At a cartilaginous joint the bones are held together sheaths.
by cartilage.
Structure of Synovial Joints
Epiphyseal (growth) Epiphysis Synovial joints (si-NŌ-vē-al) have certain characteristic
plates
distinguish them from other joints. The unique characterist
synovial joint is the presence of a space called a synovial (
Epiphysis cavity between the articulating bones (Figure 9.3). Becau
synovial cavity allows a joint to be freely movable, all sy
joints are classified functionally as diarthroses. The bone
synovial joint are covered by a layer of hyaline cartilage
articular cartilage. The cartilage covers the articulating s
Diaphysis of the bones with a smooth, slippery surface but does no
them together. Articular cartilage reduces friction between
(a) Synchondrosis in the joint during movement and helps to absorb shock.
Articular Capsule
Hip bones
A sleevelike articular (joint) capsule surrounds a synovia
encloses the synovial cavity, and unites the articulating
The articular capsule is composed of two layers, an outer fi
membrane and an inner synovial membrane (Figure 9.3
fibrous membrane usually consists of dense irregular conn
tissue (mostly collagen fibers) that attaches to the perioste
the articulating bones. In fact, the fibrous membrane is lite
Pubic
symphysis thickened continuation of the periosteum between the bone
flexibility of the fibrous membrane permits considerable
(b) Symphysis ment at a joint, while its great tensile strength (resista
stretching) helps prevent the bones from dislocating. The fi
? What is the structural difference between a synchondrosis some fibrous membranes are arranged as parallel bund
and a symphysis? dense regular connective tissue that are highly adapted for
