Classification of Joints

Question 1

What is a joint?

Answer 1

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.

Question 2

Describe how joints can be classified

Answer 2

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

Question 3

What are the three types of synovial joints?

Answer 3

• suture
• syndesmosis
• gomphosis

Question 4

Describe the suture class of synovial joints

Answer 4

• 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

Question 5

Describe the syndesmosis class of synovial joints

Answer 5

• 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

Question 6

Describe the gomphosis class of synovial joints

Answer 6

• 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

Question 7

Describe cartilaginous joints

Answer 7

Cartilaginous joints lack a synovial cavity, and the articulating bones are tightly connected by cartilage; they permit little or no movement.

Question 8

What are the two types of cartilaginous joints?

Answer 8

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

Question 9

Describe synovial joint characteristics

Answer 9

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.

Question 10

Describe planar joints

Answer 10

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

Question 11

Describe hinge joints

Answer 11

• 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

Question 12

Describe pivot joints

Answer 12

-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

Question 13

Describe condyloid or ellipsoidal joints

Answer 13

• 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

Question 14

Describe saddle joints

Answer 14

• 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

Question 15

Describe ball and socket joints

Answer 15

-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

Question 16

What are the general types of movement that occur at synovial joints?

Answer 16

-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.

Question 17

What are some special movements that some synovial joints perform?

Answer 17

-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.

Question 18

What are some factors affecting contact and range of motion at synovial joints?

Answer 18

-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

Question 19

What are the effect of aging on joints?

Answer 19

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