Joints  Formed where

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Joints  Formed where Powered By Docstoc
					 Formed where a bone joins another bone, or where a cartilage joins a bone  The closer the fit, the stronger the joint, the more restricted the movement  The looser the fit, the weaker the joint, the greater degree of movement, the greater the chance of dislocation

Functions of joints
 Hold bones together  Allow for mobility


FUNCTIONAL Classification of Joints!
 3 types of joints if we classify by the degree of movement possible:
1. Diarthroses
  Freely moveable joints Shoulder, knee, hip, elbow, interphalangeal, tarsal, and carpal joints

2. Amphiarthroses
    Slightly moveable joints Intervertebral discs, costosternal joints, pubic symphysis Joints with little or no movement Skull sutures, mental symphysis, teeth in sockets, 1st costosternal joint.

3. Synarthroses

STRUCTURAL Joint Classification
 Fibrous  Cartilagenous  Synovial

Fibrous Joints
 No synovial cavity. Two bones remain held together by thin layer of fibrous tissue or dense fibrous tissue or cement or sutures.
1. Sutures Synostoses – (Suture during infancy but fusion afterwards as in Frontal bone). Bones are thin and plate like, held together by inter digitations. e.g., skull bones. 2. Gomphosis One bone remains embedded in the socket of other attached through fibres or cement layer. e.g., Thecodont( Greek for "sockettooth ) teeth of humans.
3. Shindylases One bone fits into slit of other. e.g., ethmoid bone into vomer.

4. Syndesmosis Two bones are united by dense fibrous tissue. e.g., joint between skull bones and bones of upper jaw, distal ends of tibia and fibula.

Cartilaginous Joints
 No synovial cavity, articulating bones are united by cartilage.
1. Synchondrosis Connecting material is hyaline cartilage. e.g., temporary joint between diaphysis and epiphysis of a long bone and permanent joint between true ribs and sternum. 2. Symphysis Connecting material is broad flat disc of fibrocartilage. e.g., Intervertebral disc and symphysis pubis.

 characterized by:  articular cartilage - a protective layer of dense white connective tissue covering the articulating bone surfaces  articular capsule - a double-layered membrane that surrounds the joint  synovial fluid - a clear, slightly yellow liquid that provides lubrication inside the articular capsule  associated bursae - small capsules filled with synovial fluid that cushion the structures they separate

Functions of articular cartilage
 distributing loads over joint surfaces  improving the fit of articulations  limiting slip between articulating bones  protecting the joint periphery  lubricating the joint  absorbing shock at the joint

Types of Synovial Joints

Plane joints
Articular surfaces are flat and allow short slipping or gliding movements. Intercarpal and intertarsal joints



Hinge joints
A cylindrical projection of one bone fits into a troughshaped surface on another (like a hotdog in a bun) Movement resembles a door hinge. Elbow joint – ulna and humerus; Interphalangeal joints



Type of Synovial Joints

Pivot joints
Rounded end of one bone protrudes into a ring formed by another bone or by ligaments of that bone. Proximal radioulnar joint Atlas-axial joint

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Condyloid joints
Oval articular surface of one bone fits into a complementary depression on another. Radiocarpal joints Metacarpophalangeal joints

Types of Synovial Joints
5. Saddle joints
 Each articular surface has convex and concave areas. Each articular surface is saddleshaped. Carpometacarpal joints of the thumbs.
Spherical or semi-spherical head of one bone articulates with the cuplike socket of another. Allow for much freedom of motion. Shoulder and hip joints.


6. Ball-and-Socket joints


Joint Stability
 ability of a joint to resist abnormal displacement of the articulating bones  factors increase joint stability
 a closely reciprocating match of the articulating bone surfaces

 a strong array of ligaments and muscle tendons crossing the joint

Factors increase joint stability
 articulating bone surfaces
 wide contact area - high stability

 different among joints and individuals  change in joint angle - change in contact area - change in stability

Factors increase joint stability

 Connective tissues crossing the joint  weak and lax connective tissues low stability  strengthening of tissues - increase in stability  muscle activity and fatigue decrease in stability

Joint Flexibility
 a description of the relative ranges of motion allowed at a joint in different directions

 range of motion (ROM) - the angle through which a joint moves from anatomical position to the extreme limit of segment motion in a particular direction

Factors influence joint flexibility
Shapes of articulating bone surfaces Intervening muscle or fatty tissue Laxity Extensibility of collagenous tissue and muscles  Fluid contents in cartilagenous disc  Temperature of collageneous tissues  Stretching program    

Joints (Types of Movements at Synovial Joints)
  Specific terminology is used to designate the movements that occur at joints Movements are grouped into four main categories:
1. 2. 3. 4. Gliding Angular movements Rotation Special movements

 Gliding:
 Simple movement back-and-forth and from side-to-side  There is no significant alteration of the angle between the bones  Limited in range

 Eg., Intercarpal joints

 Angular Movements:
 Increase or a decrease in the angle between articulating bones

 Types:
      Flexion Extension Lateral flexion Hyperextension Abduction Adduction

 Circumduction:
 Movement of a body part in a circle  Moving the humerus in a circle at the shoulder joint

 Rotation:
 A bone revolves around its own longitudinal axis  Turning the head from side to side as when you shake your head “no”

 Special Movements
           Elevation Depression Protraction Retraction Inversion Eversion Dorsiflexion Plantar flexion Supination Pronation Opposition

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