JOINTS

INTRODUCTION A place where two or more bones get

articulated with one another is called a joint.

Joints help to connect different parts of skeleton and form a basic framework of body.

CLASSIFICATION OF JOINTS

1.Functional classification of jointsaccording to the movement allowed in this joints

Synarthrosis -an immovable joint Amphiarthrosis -a slightly movable joint Diarthrosis -a freely movable joint

2. The structural classification of joint Depends on the nature of intervening soft tissue presence or absence of joint cavity

Fibrous joints -bones held together by dense collagen fibers

Cartilaginous joints -bones held together by cartilage

Synovial joints -bones held together by ligaments

FIBOROUS JOINT Bones are joined by fibrous tissue No joint cavity is present Amount of movement allowed depends on

the length of the connective tissue fibers uniting the bones

A few are slightly movable but most fibrous joints are immovable

3 types

sutures syndesmoses gomphoses

SUTURES

Restricted to skull bones

The junction is completely filled by minimal amount of very short connective tissue which ossifies during middle age.

Synostosis on completion of growth

TYPES OF SUTURES

plane squamous

serrate dentate

schindylesis

SYNDESMOSIS

The bones are connected by a ligament a cord or a band of fibrous tissue.

Represented by Interosseous ligament Slender fibrous cord Dense aponeurotic membrane

The amount of movement allowed depends on the length of the connecting fibers and slight to considerable movement is possible.

Example : ligament connecting the distal end of tibia

and fibula Radioulnar syndesmosis

GOMPHOSES

It is a peg in socket fibrous joint Example is articulation of a tooth with its

bony alveolar socket The fibrous connection in this case is the

short periodontal ligament

CARTILAGINOUS JOINT

The articulating bones are united by cartilage

Like fibrous joints they lack a joint cavity

2 types

synchondroses symphyses

SYNCHONDROSES A bar or plate of hyaline cartilage unites the

bones at a synchondrosis Virtually all synchondroses are synarthrotic Example coastal cartilage of the first rib and

the manubrium of the sternum

The articular surfaces of the bones are covered with articular cartilage which in turn is fused to an intervening pad or plate of fibrocartilage.

Limited amount of movement at the joint Example the intervertebral joints and the

pubic symphysis of the pelvis

SYNOVIAL JOINTS Articulating joints are those in which the

articulating bones are separated by a fluid containing joint cavity.

All synovial joints are freely movable diarthroses.

ARTICULAR CARTILAGE

Glassy smooth hyaline cartilage covers the opposing bone surfaces

Spongy cushions absorb compression and prevent the bones from crushing.

ARTICULAR CAPSULE

The joint cavity is enclosed by two layered articular capsule.

External layer is tough fibrous capsule which strengthens the joint so that the bones are not pulled apart.

The inner layer of the joint capsule is a synovial membrane composed of loose connective tissue.

SYNOVIAL MEMBRANE

Very thin highly vascular membrane made of connective tissue cells and fibers.

On the basis of structural variation

Fibrous type -when it is adherent to fibrous capsule

Adipose type -when it is found over inter articular fat pads

Areolar type -which allows mobility of synovial membrane

Functions Synovial membrane secretes and also

absorbs synovial fluid. It has phagocytic action so protects the joint

cavity

SYNOVIAL FLUID

Small amount of slippery synovial fluid occupies all free spaces within the joint capsule.

Derived by filtration from blood flowing through the capillaries in the synovial membrane

Viscous ,clear or pale yellow due to its content of hyaluronic acid secreted by cells in the synovial membrane, but it thins, becoming less viscous as it warms during joint activity.

Highly alkaline in nature

Functions Reduces friction between the cartilages. It also contains phagocytotic cells It provides nutrition to the articular

cartilage It acts as shock absorber.