Classification of Joints Flashcards
What is a joint?
A joint or articulation or arthrosis is a point of contact between neighbouring bones, between cartilage and bones, or between teeth and bones. The structural characteristics of a specific joint affect the strength, magnitude of movement, and types of movement that may occur at a specific joint.
Describe how joints can be classified
Based on the presence or absence of a synovial cavity and the type of connective tissue that binds the bones together, the structural classification of joints categorizes joints into three major types:
- fibrous
- cartilaginous
- synovial
Based on the magnitude of movement permitted, the functional classification of joints categorizes joints into three major groups:
- synarthrosis is an immovable joint
- amphiarthrosis is a slightly movable joint
- diarthrosis is a freely movable joint
What are the three types of synovial joints?
- suture
- syndesmosis
- gomphosis
Describe the suture class of synovial joints
- consists of a thin layer of dense fibrous connective tissue that strongly connects the bones
- is located exclusively between neighbouring skull bones (e.g. coronal suture)
- functionally classified as a synarthrosis
- a synostosis is a childhood suture that is replaced by bone in the adult
Describe the syndesmosis class of synovial joints
- contains more fibrous connective tissue than in a suture
- an example is the distal articulation between the tibia and fibula
- functionally classified as an amphiarthrosis
Describe the gomphosis class of synovial joints
- a joint in which a cone-shaped peg fits into a socket
- the only example is the periodontal ligament which connects the root of a tooth to the alveolus of the mandible or maxilla
- functionally classified as a synarthrosis
Describe cartilaginous joints
Cartilaginous joints lack a synovial cavity, and the articulating bones are tightly connected by cartilage; they permit little or no movement.
What are the two types of cartilaginous joints?
Synchondrosis:
- the connecting tissue is hyaline cartilage
- an example is an epiphyseal plate
- functionally classified as a synarthrosis
Symphysis:
- the connecting tissue is a disc of fibrocartilage
- an example is the pubic symphysis
- functionally classified as an amphiarthrosis
Describe synovial joint characteristics
Synovial joints are characterized by the presence of a synovial (joint) cavity; they are functionally classified as diarthroses. Additional important characteristics include:
-articular cartilage
-articular capsule composed of two layers; outer fibrous capsule that may have ligaments and inner synovial membrane which secretes the lubricating synovial fluid that fills the synovial cavity
-Many synovial joints also contain accessory ligaments, including extracapsular ligaments and intracapsular ligaments
-articular discs or menisci rich blood and nerve supply
Fluid-filled sacs called bursae and tube-like bursae called tendon sheaths reduce friction at some joints during movements.
Describe planar joints
planar joint
- at which gliding movements may occur
- articulating surfaces are usually flat or slightly curved
-only side-to-side and back-and-forth movements are permitted without movement around any axis; it is a nonaxial joint
-an example is the sternoclavicular joint
Describe hinge joints
- monaxial or uniaxial joint at which the convex surface of one bone fits into the concave surface of another bone
- flexion and extension (and sometimes hyperextension) may occur
- examples include the knee joint, elbow joint, and ankle joint
Describe pivot joints
-monaxial joint at which rounded or pointed surface of one bone articulates within a ring formed partly by another bone and partly by a ligament
-rotation may occur
-an example is rotation of the atlas around the dens of the axis when
turning the head
Describe condyloid or ellipsoidal joints
- biaxial joint at which the oval-shaped condyle of one bone rests against the elliptical cavity of another bone
- the four angular movements (and circumduction) may occur
- an example is the wrist joint
Describe saddle joints
- biaxial joint at which articular surface of one bone is saddle-shaped and the articular surface of the other bone resembles the legs of a rider sitting in a saddle
- is technically a modified ellipsoidal joint in which movement is less restricted
- an example is the joint between the trapezium and the base of the first metacarpal
Describe ball and socket joints
-multiaxial (or polyaxial) joint at which the ball-like surface of one bone
rests against the cuplike depression of another bone
- the four angular movements and rotation may occur
- the only examples are the shoulder and hip joints
What are the general types of movement that occur at synovial joints?
-gliding movements in which articulating surfaces slide across each other
-angular movements; in which there is a change in the angle between
articulating bones. Examples include flexion, extension, abduction, adduction, and circumduction (a movement in which the distal end of a bone moves in a circle while the proximal end remains stable; it is typically a combination of the four angular movements and rotation).
-rotation; in which a bone turns around its own longitudinal axis. There are two types: medial (or internal) rotation and lateral (or external) rotation.
What are some special movements that some synovial joints perform?
-elevation and depression are, respectively, an upward movement of a
part of the body (e.g., elevating the mandible to close the mouth), and a downward movement of a part of the body (e.g., depressing the mandible to open the mouth)
- protraction and retraction are movements of the mandible or shoulder girdle forward or backward, respectively, on a plane parallel to the ground
- inversion and eversion are movements of the sole of the foot medially or laterally, respectively
- dorsiflexion and plantar flexion are bending of the ankle joint so that the foot moves in a dorsal or plantar (sole) direction, respectively
- supination and pronation are movements of the forearm in which the palm turns anteriorly/superiorly or posteriorly/inferiorly, respectively
- opposition is the movement of a thumb across the palm to touch the fingertips on the same hand.
What are some factors affecting contact and range of motion at synovial joints?
-structure or shape of the articulating bones
-strength and tension (tautness) of the joint ligaments
-arrangement and tone of muscles around the joint
-apposition of neighbouring soft tissues
-effect of hormones (e.g., relaxin relaxes pelvic joints toward the end of
pregnancy)
-disuse of a joint
What are the effect of aging on joints?
The effects of ageing on joints are variable among individuals and are affected by genetic factors and wear and tear; the ageing process usually results in:
-decreased production of synovial fluid
-thinning of articular cartilage
-shortening of ligaments and a decrease in ligamentous flexibility
-degenerative changes in load-bearing joints
