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Joints of The Human Skeleton Bones - Why Are They Movable?

If the body did not have joints, we would not be able to move. 

Than we could only lie completely motionless, unable to move our head, to walk, to raise our hands or move only one finger!

All this we can do through the joints.

Everywhere where two bones slide over one another, there is a joint. The joint allows the bones to move smoothly with little friction, because the ends of the bones are covered with cartilage, so that the bones do not rub against each other.
In addition, the joint is whitish liquid, thick as a living egg, synovial fluid, and it plays the role of lubricating the machine, which reduces friction.
When the joint is at rest, it generates very little synovial fluid and joint becomes really creaky.

Types of joints

In the human body there are four types of joints:
  • angular, 
  • egg-shaped, 
  • in the form of hinge joints and 
  • rotary joints. 
Shoulder joint, which is spherical, is the most mobile of all the joints in the body. Therefore, we can run hand in all directions.
The hip joint is the largest ball joint, but because it is deeper, it is not so mobile.
The second type is egg-shaped joint.
This joint has an ovoid surface, which retracts into the appropriate socket. One form of this type is the saddle-shaped joint, in which the bones can only move in two directions, as a rider in the saddle. This type of joint we have in the spine, which can only bend in two directions, forward and from one side to the other.

The third type of joint is the joint in the form of hinges. These bones can only move back and forth in a plane, such as a door or a pocket knife.

The fourth type is the rotary joint. It allows bones to rotate. Rotary joint at the base of the skull we have, so we can turn our head and wrist to the elbow, which allows us to turn the key in the lock.

What are slightly mobile joints?

At a typical slightly mobile joint, the bones have a layer of cartilage between them and are held firmly together by strong ligaments. Such joints are found between the pubic bones (symphysis pubis) and the disks between the vertebrae of the spine.

What are immobile joints?

Immobile joints occur where two bones are fused or fixed together before or shortly after birth. Examples are the ilium, pubis, and ischium, which together form the hipbone, and the many flat bones that combine to make up the skull.

Joint disorders

There are many conditions that may involve joints:
  • Degenerative conditions, such as osteoarthritis;
  • Inflammatory conditions, such as rheumatoid arthritis;
  • Conditions involving the membranes surrounding the joints, such as synovitis;
  • Generalized disorders involving the joints, such as gout;
  • Damage to the joint involving dislocation or complicated fracture;
  • Congenital disorders, including congenital dislocation of the hip and clubfoot.






Perthes’ disease polyarthritis


rheumatic fever


shoulder, frozen




spondylitis, ankylosing

Disk, herniated   





spondylosis, cervical






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