Joints - OpenStax CNX

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Joints
∗
Tonye A. Ogele
This work is produced by OpenStax-CNX and licensed under the
Creative Commons Attribution License 3.0†
Abstract
By the end of this section, you will be able to • Dene a joint • Classify the dierent types of joints
on the basis of structure
1.0 INTRODUCTION
A joint is a point where two or more bones meet. The joint may be movable or immovable. An example
of a joint is the knee joint which is a movable joint between the femur and the tibia (gure 1). Sutures are
immovable joints in the skull (gure 2).
Figure 1: The knee joint.
∗ Version
1.2: May 6, 2013 4:41 pm -0500
† http://creativecommons.org/licenses/by/3.0/
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Figure 2: Sutures of the skull.
2.0 STRUCTURAL CLASSIFICATION OF JOINTS
The structural classication of joints is based on the type of binding tissues that hold the bones together.
On this basis, joints can be classied into bony joints, brous joints, cartilaginous joints and synovial joints.
2.1 BONY JOINTS (SYNOSTOSES)
A bony joint or synostosis is formed when the space between two bones ossies to form a single bone. In
other words, the bones fuse to form one bone. Bony joints are former brous joints or cartilaginous joints.
An infant for example, is born with a right frontal bone and a left frontal bone separated by the frontal
suture (gure 3). By 6 years these bones have fused to form a single frontal bone (gure 4). The infant also
has two mandibular bones which fuse to form a single mandible.
Figure 3: The skull of an infant. The frontal suture separates the left and right frontal bones.
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Figure 4: The skull of an adult with a single frontal bone.
In the long bones of children, one can identify the growth plate or epiphyseal plate as the cartilage that
connects the parts of the long bone (epiphysis and diaphysis or shaft) together (gure 5 and gure 6). This
forms a cartilaginous joint (discussed below). In early adulthood, the cartilage disappears leaving a bony
epiphyseal line. The diaphysis and epiphyses are seen fused together to form a single bone (gure 7).
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Figure 5: A long bone showing the epiphyses and the diaphysis (shaft).
Figure 6: X-ray of the tibia and bula showing the growth plate.
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Figure 7: Diagram of a long bone showing the epiphyseal (epiphysial) line.
Also in old age, some cranial sutures disappear. Thus adjacent cranial bones fuse to form a single bone.
For example the sagittal suture separating the parietal bones (labeled as 2 in gure 8) can disappear. The
result is a single parietal bone. The attachment of the rst rib to the sternum also becomes a bony joint
with age.
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Figure 8: Superior view of the skull showing the parietal bones separated by the sagittal suture (2)
2.2 FIBROUS JOINTS
In the brous joint, the bones are held together by collagen bres that emerge from one bone and
penetrate the other bone. There are three types of brous joints: sutures, gomphoses and syndesmoses.
2.2.1 SUTURES
Sutures are brous joints between the bones of the skull (gure 2). The collagen bres binding the
bones together in sutures are very short, so that the bones are held tightly together and do not move.
2.2.2 GOMPHOSES
A gomphosis is a brous joint between a tooth and the bone (mandible below or maxillae above) (gure
9). The tooth is held in the socket by periodontal ligaments which are made of collagen bres, that extend
from the bone to the tissue of the tooth. The periodontal ligaments allow the tooth to move slightly under
pressure of chewing.
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Figure 9: The jaw bone and the teeth.
2.2.3 SYNDESMOSES
Syndesmoses are movable brous joints. This is due to the longer bres that hold the bones of the
joints together. An example of syndesmoses is the joint at the distal ends of the tibia and bular (i.e. the
joint of the tibia and bular at the ankle). Another example is the joint between the shafts of the ulna and
the radius. This joint is held by a broad brous sheet called the interosseous membrane (gure 10).
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Figure 10: Diagram showing interosseous membrane.
2.3 CARTILAGINOUS JOINTS
Cartilaginous joints are joints in which the bones are connected by cartilage. There are two types of
cartilaginous joints: sychondroses and symphyses.
2.3.1 SYNCHONDROSES
A synchondrosis is a cartilaginous joint in which the bones are bound by hyaline cartilage. An example
is the temporary joint between the epiphysis and diaphysis of a long bone in a child, which is formed by
a hyaline cartilage called the epiphyseal plate. This joint will later become a bony joint as the cartilage
changes to bone. The joint between the rst rib and the sternum is also a synchondrosis. This joint also
changes to a bony joint at old age.
2.3.2 SYMPHYSES
A symphysis is a cartilaginous joint in which the bones are joined by brocartilage. An example is
the pubic symphysis which joins the right and left pubic bones of the pelvis by the cartilaginous interpubic
disc (gure 11). Also the joints between the vertebral bones which are joined by the intervertebral discs are
symphyses.
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Figure 11: The pelvic bone
2.4 SYNOVIAL JOINTS
Synovial joints have the most complex structure of all the types of joints. The bones forming the synovial
joint do not meet but are separated by a space called the synovial cavity, joint cavity or articular cavity. The
synovial cavity is enclosed by the articular capsule or joint capsule. The joint capsule allows for movement of
the bones forming the joint but prevents dislocation of the bones of the joints. The joint capsule is made up
of an outer brous capsule and an inner synovial membrane. The synovial membrane secretes the synovial
uid which lls the synovial cavity (gure 12).
The synovial uid is a uid with a slippery texture like raw egg white. It is a mixture polysaccharides
(complex carbohydrates), proteins, fats and phagocytes. This uid acts as a lubricant for the joint, provides
nutrition for the cartilages of the joint and removes their waste, and the phagocytes in the uid remove
microbes and particles of cartilages that break o due to wear and tear.
The bone surfaces in the synovial joint are covered with hyaline cartilage called the articular cartilage.
The articular cartilage provides a smooth articular surface for the joint and together with the synovial uid
makes movement at the synovial joints almost friction-free.
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Figure 12: Synovial joint.
Based on the shape of the articular surfaces which aects movement, synovial joints are classied into
6 dierent categories: ball-and-socket joints, condyloid joints, saddle joints, gliding joints, hinge joints and
pivot joints.
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Figure 13: Types of synovial joints.
2.4.1 BALL-AND-SOCKET JOINTS
The ball-and-socket joint is made up of a round, ball-like end of one bone which ts into the cup-like
socket of another bone (gure 13). This joint allows for the greatest range of movements because it is the
only multiaxial joint in the body. The ball-and-socket joint can thus move in dierent planes: exion and
extension, adduction and abduction, and medial rotation and lateral rotation. Circumduction is also possible
with ball-and-socket joints.
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Figure 14: X-ray of the hip joint.
Examples of the ball-and-socket joints are the hip joint and the shoulder joint (gure 14). In the hip
joint the femur has the ball-like end that ts into the cup-like socket of the pelvis. While in the shoulder
joint (gure 15), the humerus has the ball-like end that ts into the cup-like socket of the scapula.
Figure 15: The shoulder joint.
2.4.2 CONDYLOID JOINTS (ELLIPSOID JOINTS)
The condyloid joint (gure 13) is an elongated ball-and-socket joint. It has an oval convex surface
on one bone that ts into a similarly shaped depression on the other bone. Condyloid joints are biaxial
joints i.e. they are capable of moving in two planes: exion and extension, and adduction and abduction.
Circumduction is possible with condyloid joints. Examples of the condyloid joints are the radiocarpal joint
(joint between the radius and the carpal bones) of the wrist and metacarpophalangeal joints (joints between
the metacarpals and phalanges) at the base of the ngers (gure 16).
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Figure 16: The metacarpophalangeal joint.
2.4.3 SADDLE JOINTS
A saddle joint (gure 13) is made up of articulating surfaces of bones, each of which is concave in one
direction and convex in the other, like a saddle, and both of which are at right angles to each other. Saddle
joints are biaxial like condyloid joints, but have a greater range of movement. Examples of saddle joints
are the sternoclavicular joint (joint between the sternum and the clavicle) and the trapeziometacarpal joint
(joint between the trapezium a carpal bone and the metacarpal) at the base of the thumb (gure 17).
Figure 17: The trapeziometacarpal at the base of the thumb.
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2.4.4 GLIDING JOINTS (PLANAR JOINTS)
The articulating surfaces of gliding joints (gure 13) are at or slightly concave and convex. The bones
therefore slide over each other with limited movements. The joints are biaxial, though movements are slight.
Their combined eect however, give a signicant overall movement. Examples of gliding joints are the joints
between the carpal bones of the wrist and the joints between the tarsal bones of the ankle.
Figure 18: Carpal bones.
2.4.5 HINGE JOINTS
In the hinge joint (gure 13), one bone has a convex surface that ts into a concave depression in the
other bone. The hinge joint is a monoaxial joint i.e. movement is possible in only one plane: exion and
extension. Examples of hinge joints are the elbow joint (gure 19), knee joint (gure 1) and interphalangeal
joints (gure 16).
Figure 19: Elbow joint.
2.4.6 PIVOT JOINTS
The pivot joint (gure 13) is a synovial joint in which a cylindrical part of a bone rotates in a ring formed
by another bone and a ligament. For example in the proximal radioulnar joint (joint between the radius and
ulnar at the elbow) the ulnar and the anular ligament forms a ring that wraps round the neck of the radius
(gure 20). In pronation and supination of the forearm the head of the radius rotates within the ring.
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Figure 20: The radioulnar joint.
The atlantoaxial joint (joint between atlas and axis) is another example of a pivot joint.
PICTURE ATTRIBUTIONS
Figure 1 Lynch, P. J. (2006, December 23). Knee skeleton diagram. Retrieved from Wikipedia Website:
http://en.wikipedia.org/wiki/File:Knee_skeleton_lateral_anterior_views.svg1
Figures 2, 5, 9, 13, 15, 16, 17, 18, 19 OpenStax College (2013, April 10). Joints and Skeletal Movement.
Retrieved from the Connexions Website: http://cnx.org/content/m44786/1.3/
Figure 3 Anatomist90 (2013, January 22). Anatomical dissections. Retrieved from Wikipedia Website:
https://en.wikipedia.org/wiki/File:Slide1MIA.JPG2
Figure 4 Gray, H. (1918) Anatomy of the Human Body. Philadelphia: Lea & Febiger. Retrieved from
Wikipedia Website: http://en.wikipedia.org/wiki/File:Gray190.png3
Figure 6 Gilo 1969 (2009, December 8)Xray of lower leg of 12 year old child showing growth plates.
Retrieved from Wikipedia Website: http://en.wikipedia.org/wiki/File:Tib_b_growth_plates.jpg4
Figure 7 Gray, H. (1918) Anatomy of the Human Body. Philadelphia: Lea & Febiger. Retrieved from
Wikipedia Website: http://en.wikipedia.org/wiki/File:Gray209.png5
Figure 8 Kollmann, J. (1910) Plastische Anatomie des menschlichen Körpers für Künstler und Freunde der
Kunst. (3rd ed.) Leipzig. Retrieved from Wikipedia Website: http://en.wikipedia.org/wiki/File:Kort-lang-skalle.gif6
Figure 10 Gray, H. (1918) Anatomy of the Human Body. Philadelphia: Lea & Febiger. Retrieved from
Wikipedia Website: http://en.wikipedia.org/wiki/File:Gray420.png7
1 http://en.wikipedia.org/wiki/File:Knee_skeleton_lateral_anterior_views.svg
2 https://en.wikipedia.org/wiki/File:Slide1MIA.JPG
3 http://en.wikipedia.org/wiki/File:Gray190.png
4 http://en.wikipedia.org/wiki/File:Tib_b_growth_plates.jpg
5 http://en.wikipedia.org/wiki/File:Gray209.png
6 http://en.wikipedia.org/wiki/File:Kort-lang-skalle.gif
7 http://en.wikipedia.org/wiki/File:Gray420.png
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Figure 11 Anatomist90 (2012, December 23) Anatomical dissections. Retrieved from Wikipedia Website:
http://en.wikipedia.org/wiki/File:Slide3ADA.JPG8
Figure 12 Retrieved from Wikipedia Website: http://en.wikipedia.org/wiki/File:Illu_synovial_joint.jpg9
Figure 14 User:Scuba-limp (2005, October 26) Normal hip joint. Retrieved from Wikipedia Website:
http://en.wikipedia.org/wiki/File:Hueftgelenk-gesund.jpg10
Figure 20 Gray, H. (1918) Anatomy of the Human Body. Philadelphia: Lea & Febiger. Retrieved from
Wikipedia Website: http://en.wikipedia.org/wiki/File:Gray331.png11
REFERENCES
OpenStax College (2013, April 10). Joints and Skeletal Movement. Retrieved from the Connexions
Website: http://cnx.org/content/m44786/1.3/
Saladin, K. S. (2007) Anatomy and physiology: The unit of form and function. (4th ed.) New York:
McGraw-Hill.
Seeley, R. R., Stephens, T. D. & Tate, P. (2002) Essentials of anatomy and physiology (4th ed.) New
York: McGraw-Hill.
Waugh, A. & Grant, A. Ross and Wilson anatomy and physiology in health and illness Philadelphia:
Churchill Livingstone Elsevier.
8 http://en.wikipedia.org/wiki/File:Slide3ADA.JPG
9 http://en.wikipedia.org/wiki/File:Illu_synovial_joint.jpg
10 http://en.wikipedia.org/wiki/File:Hueftgelenk-gesund.jpg
11 http://en.wikipedia.org/wiki/File:Gray331.png
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