JOINTS

INTRODUCTION OF JOINTS

  • Joint is a junction between two or more bones or cartilages. It is a device to permit movement.
  • With the exception of hyoid bone, every bone in the body is connected to or forms a joints .
  • There are 230 joints in the body

FUNCTIONS OF JOINT

  • Hold the skeletal bones together .
  • Allow the skeleton some flexibility so gross movement can occur.
  • Make bone growth possible.

CLASSIFICATION OF JOINTS

  • Joints are classified into structural and functional.
  • Structural  classification is determined by how the bones connect to each other ,while functional  classification is determined by the degree of movement between the articulating bones .

STRUCTURAL CLASSIFICATION OF JOINTS

FIBROUS

(FIXED)

A. Sutures

1.Plane

2.Squamous

3.Serrate

4. Dentate

5.Schindylesis

B. Gomphosis

C. Syndesmosis

Cartilaginous

(slightly  movable)  

a.Primarily Cartilaginous joints (synchondrosis)

b. Secondary cartilaginous joints (symphysis)

Synovial

( Freely movable) 1.Plane

2.Hinge

3.Pivot

4.Bicondylar

5.Ellipsoid

6.Saddle

7.Ball and socket

Fibrous joints : 

Fibrous joints – Bones are joined by fibrous tissue /dense connective  tissue , consisting mainly of collagen . The fibrous joints are further divided into three type:

Sutures or synostoses :- Found between bones of the skull . In fetal skulls the sutures are wide to allow slight movement during birth . They later become rigid (synarthrodial).

Syndesmoses:-  joints where two   adjacent bones  joins together by a greater amount of connective tissue than in sutures in the form of interosseous ligaments and membranes .

eg – interosseous radioulnar joint interosseous tibiofibular joint

Gomphosis:- It is a specialized fibrous  joint restricted to fixation of teeth in alveolar sockets of the maxilla or mandible. The root of tooth is attached to the socket with in alveolus by periodontal ligament

CARTILAGNOUS JOINTS

In this type of joint the bones are joined by cartilage.

There are two types of cartilaginous  joints :

1.Primary cartilaginous  joints

2.Secondary cartilaginous joints

PRIMARY CARTILAGE

•Joints – known as “synchondroses”.

•Bones forming joints are connected by a plate of hyaline cartilage .These joints are immovable and mostly temporary in nature .

•This cartilage may ossify  with age .

•Example in humans are the joint between the first rib and the manubrium of the sternum.

•Joint between epiphysis and diaphysis of growing long bone .

SECONDARY CARTILAGE

•Known as “symphysis” . In these joints  the articular surfaces of bone forming the joints are covered by tin plates of hyaline cartilage ,which are connected by a disc of  fibrocartilage

•Example :-symphysis pubis •Intervertebral  disc •Manubriosternal  disc •Symphysis menti.

SYNOVIAL JOINTS

These joints possess a cavity and articular ends of bones forming the joint  are enclosed in a fibrous capsule . As a result  they are separated by a narrow cavity , the articular cavity , which is filled  with a fluid called synovial fluid .

CHARACTERSTIC FEATURES

  • The articular surfaces are covered by a thin plate of hyaline cartilage.
  • The joint cavity is enveloped by an articular capsule which consists of outer fibrous capsule and inner synovial membrane.
  • The cavity of joint is lined everywhere by Synovial membrane except over articular cartilages.
  • The cavity is filled with the Synovial fluid secreted by Synovial membrane which provides nutrition to articular cartilage and lubrication of articular surfaces.
  • Some joint cavities are completely or incompletely divided by articular disc /menisc.

TYPES OF SYNOVIAL JOINTS

  • Plane joint
  • Hinge joint
  • Pivot joint
  • Condylar joint  
  • Ellipsoid joint
  • Saddle joint
  • Ball and socket joints

human skeleton model
  1. PLANE JOINT :-
  • Articular surfaces are more or less flat.
  • They permit gliding movements in various directions.
  • Example:- intercarpal joints ,intertarsal joints ,joints  between articular process of adjacent vertebrae.

2. HINGE JOINT :-

  • the articular surface are pulley shaped. This type of joint permits movement in one plane around transverse axis. This the movement consists of flexion and  extension.
  • These joints have strong collateral ligaments  to prevent other movements.  Two examples are the elbow joint, knee joint, interphalangeal joint ,ankle joint.

3. PIVOT JOINT :-

  • The articular surface of one bone is rounded and fits into concavity  of another bone. Further , the rounded part is surrounded by a ligamentous ring.
  • Moment is limited to the rotation around  a central axis .
  • Examples of this type of joint are the joint between the proximal end of the radius and ulna. Atlanto axial joint.

4. CONDYLAR JOINT :-

  •  The round articular surface of a one bone fits into socket type articular surface of another bone.
  •  The end of bone bearing  round articular surface is called condyle .These joints permit movement in 2 directions .
  • Example:- right and left temporomandibular joints, knee joints

5. ELLIPSOID JOINT :

  • Elliptical convex surface of one bone articulates with elliptical concave  surface of another bone .
  • The movements are permitted in two directions.
  • Eg ; wrist joints , atlanto occipital joint, metacarpo phalangeal joints, metatarso phalangeal joint

6. SADDLE JOINT

  • Saddle joint : The articular surfaces are  reciprocally saddle shaped i.e. concavo- convex this unique articulation is modified Condyloid joints that allows a wide range of movement.
  • An example would be the joint between the trapezium and the Matacarpal bones of the thumb, sternoclavicular joints .

7. BALL AND SOCKET JOINT:-

  •  It consists of a bone with a ball shaped head that attaches with the Cup shaped cavity of another Bone.
  • This type of joint allows for wider range of motion than any other kind.
  •  It permits movement in all planes, and rotational movement around a central axis.
  •  Two example of this type of joint would be the hip, shoulder joint and incudostapedial joint .

Functional  classification

  • Synarthrosis :-  Synarthrosis permit little or no mobility . Most Synarthrosis joints are fibrous joints . Eg :cranial sutures in adult .
  • Amphiarthrosis :-amphiarthrosis permit slightly mobility. The two bone surfaces at the joint are both covered in hyaline cartilage  and joined by strands of fibrocartilage. eg : secondary cartilaginous joint .
  •  Diarthrosis :-permit a variety of movements. Only synovial joints are diarthrodial.

Classification according to number of articulating  bones

  •  Simple joint : 2 articulation surfaces (eg . shoulder joint , hip joint)
  • Compound joint:- 3 or more articulation surfaces (eg radiocarpal joint )
  • Complex joint:- 3or more articulation surfaces and an articular disc or meniscus(eg knee joint )

PARTS OF A JOINTS

  • A. Fibrous Capsule
  • B.  Reinforcing ligaments
  • C.  Synovial membrane
  • D. Articular cartilage
  • E.  Articular  discs
  • F.   Fatty pads
  • G.    Bursae: flattened sacs that contain synovial fluid . function to reduces friction.

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4 Comments.

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