parts of joint

What is joint? The part of our body where arthritis occurs.

To answer the question what is arthritis you have to understand what is joint? and to understand it you have to know the concept that we as human being are not trees or mountains which has to stay at a single place and live our life.

Why we need bones

Humans need movement to perform their daily activities. For this reason our flesh of body which are mostly muscles play a significant role in movement . To perform movement actions muscles need some solid and strong thing on which they can perform the action of movement. For this reason God has made our bones.

why skeleton has multiple bones

Now if our skeleton would have been a single hard structure. our range of movement would be less . so to increase the range of motion and diverse movements our skeleton has been broken down into multiple 206 bones to increase the range of movements.

why skeleton has joints?

when two or more bones meet at a point they form a joint. as we know that when two things rub or slide on each other they face resistance. similarly when two bones move on one and other they face friction. If there is not enough lubrication our bone become short with time. So its presence is essential because when two bones move on one and other they face resistance.

So this specialized structure decreases friction.

How many Joints in human body

First of all you should know that the no of joints is human body varies. like in childhood we have more joints in our body . When we grow up our body small cartilaginous bones fuses with each others and number of joints decreases. how ever it is estimated that human body contains 250 to 350 joints in our body.

Functions of joint.

It seems like it has to perform following functions :

  • Allow range of movement
  • Decrease friction
  • Protect bone ending’s from erosion
  • Absorb vibrations
  • Transmit weight
  • Provide Fluid for Lubrication
  • Protect the joint cavity from pathogens
  • stability of skeleton

Joints parts names

Following are the major parts which makes a joint structure

  • Cartilage. First of all endings of bones have smooth, gelatinous covering called cartilage.
  • Synovial membrane. It is the lining of the inner side of joint cavity which has many functions
  • Capsule. This surrounds the joint and form a cavity.
  • Ligaments. Attached from first bone to second bone and surrounds all sides of joint to provide strength .
  • Tendons. A muscle is attaches to bone through tendon
  • Bursas. It is a fluid containing sac. it reduces friction.
  • Synovial fluid. It is the lubrication fluid in cavity and reduce friction.
  • Meniscus. Finally a pad of cartilage which provides cushion effect between two bones it is found in knee.

Classification of Joints

A- Functional classification(according to degree of mobility)

1- Synarthrosis

These are immobile joints . synarthrosis joint example is fibrous joints found in our ribs.

2-Diarthrosis

they provide more range of mobility therefore these are called freely mobile . Diasrthrosis joint example is synovial joints.

3- Amphiarthrosis

Because they provide less mobility so they are called slightly movable joints. Amphiarthrosis joint example is cartilaginous joints.

B- Structural Classification

1-Cartilaginous joints

These are further divided into

a- Primary or synchondrosis in these joints bones are united with a cartilagenous plate so that they are immobile . they are strong. they are temporary in early life and disappear after some time. example of synchondrosis is spheno-occipital, first chondrosternal joint.

b- Secondary or Symphysis in these joints the surface of bones is covered by thin hyaline cartilage. these joints are united by a fibrocartilagenous disck. they are not temporary . they remain whole life. The example of symphysis is intervertebral joints, manubriosternal joint.

2-Fibrous Joints

These have further types

a- Syndesmosis these are fibrous joints. Bone i connects with each other by interosseous ligaments. Example of syndesmosis is inferior tibiofibular joint.

b- Suture these are found in skull.

c-Gomphosis this kind of fibrous joinst are called peg and socket joints. example of gomphosis joint is tooth in its body socket.

3- Synovial Joints 

These joints are most evolved joints in human body. These have further many types

a-Ball and socket their shape is spheroidal. They allow flexion and extension, abduction and abduction, and additional circumduction and rotatory movements. they have a globular head which is fitted in cup shaped socket. example of ball and socket joints is shoulder , hip and talo-calcaneonavicular joint.

b- Hinge these are uni-axial joints. they allow flexion and extension movements only in one plane. Their articular surface is pulley shaped that is why they allow only one directional movement. Example of hing joints include ankle, elbow and interphalangeal joints found in our arms and fingers.

c- Sellar or saddle These are types of Multi-axial joints which allow flexion and extension, abduction and abduction and conjunct rotatory movements.

d-Condylar or bicondylar These are bi-axial joints which allow flexion,extension and some degree of rotation. Examples of condylar joints include knee and right and left jaw joint.

c-ellipsoid these are biaxial joints and just like condylar joints allow flexion,extension,abduction,adduction and circumduction types of moments. Examples of ellipsoid are wrist joint, metacarpophalangeal and atlanto-occipital joints.

e-pivot These are uni axial joints. pivot joints allow only rotatory movements. examples of pivot joint include superior and inferior radio-ulnar joints and median atlanto axial joints.

f-plane these are pale or gliding type of joints and allow only gliding movements. examples of plane joints include intercarpal, intertarsal joints.

C- Regional Classification

1-Skull type

  • Skull type These kind of joints are immobile.They are present in skull or head bones. they are mobile in childhood life. Thus allow molding of baby head bones as a result the safe delivery during birth. in later life they become fuse to form a single skull bone.

2- Vertebral type

  • Vertebral type these joints are slightly movable. Specialized joints which not only allow mobility but also cushion effect. But intervertibral discs between them. which act as shock absorbents. it also transmit weight of upper limb(hands) , skull and chest to the lower limb without damaging the spinal cord.

3- Limb type these are freely movable. like joints fount in our upper limb and lower limb like shoulder and knee joint.

Mechanism of lubrication of articular cartilage

A joint needs a perfect lubrication to avoid friction and allow movement thought life of a human being. so following mechanisms of lubrication occurs to lubricate articular cartilage:

1- Synovial fluid 

  • Synovial fluid synovial membrane produces synovial fluid . its main component is hyaluronic acid . it provides lubrication as well as nutrients to the joints. along with that is removes waists products from the joint.

2- Intra-articular Fibrocartilage

  • Intra-articular Fibrocartilage these are menisci which spreads synovial fluid in joint cavity.

3- Hyaline Cartilage

  • Hyaline Cartilage its slippery property provides lubrication. its is covering of the articular bones.

4- Haversian Fatty Pads

  • Haversian Fatty Pads provide lubrication. they covers with synovial membranes . they also produce synovial fluid in joint cavity.

Joint Stability Factors

Following are the factors which provide stability :

  • Muscles joint stability is mainly provided by muscles. muscles isometric tones maintain the joint in and appropriate position.
  • Ligaments are in more close proximity to any knee . they prevent sudden stretch stress and trauma to cause damage to joint’s stability.
  • Bones help to maintain stability in joints which have bones in close proximity to each other like skull bones.

Joints Problems

1- Dislocation

  • Dislocation of joints is most common problem .Direct trauma , fall, blow, jerk or weakness of joints structures are the causes of dislocation of joints. Subluxation occurs when there is no displacement of joint. Dislocation signs and symptoms include pain, deformity and loss of functions. X-ray confirms dislocation.

2- Sprain

  • Sprain is ligament teat around the joint. Sprain does not mean dislocation or fracture . This causes sever pain at the site of ligament tear and whole joint.

3- Stiffness of joint

  • During cold weather the synovial fluid viscosity increases. which causes difficulty in joint movement . As a result its stiffness occurs. This also a feature of rheumatoid arthritis.

4- Neuropathic Joint

  • Neuropathic Joint this is the complete destruction of the joint . In this all reflexes are lost. Joints become more prone to mechanical damage. This is a common feature of Tabes dorsalis, syringomyelia

5- Arthritis

  • Arthritis is inflammation of joint. this is either related to long standing diseases like rheumatoid arthritis, tuberculous arthritis or my be related to trauma, septic arthritis.

Nutrition Of Joint Health

Nutritional supply maintains joints Health. Following factors maintains its health.


1- Blood Supply

  • Blood vessels around the joint supply blood to it and surrounding structures. This in turn provides nutrients to the joint.


2- Synovial Fluid

  • Synovial Fluid secreted by synovial membrane is rich in nutrients. This synovial fluid brings nutrients along with it to keep joint healthy.

Limitation of Movements at joint

Following are the factors which can limit the movement:

  • ligament tension
  • soft part appropriation
  • mechanoreceptors stimulation in articular tissue
  • reflex contraction of antagonist muscles surrounding the joint.

Movements of joint

Following moments can occur at joint”

  • Angular moments : Flexion,extension,abduction, adduction
  • Circumduction
  • Rotation: conjunct rotation, adjunct rotation

What do you know about a joint and arthritis . comment below to have exciting reply.

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