Joints - Types, Semi-movable, Immovable, Hinge, Bone Conditions

Joints:The Center of Movement

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 18 Jan 2014 - 11:34.
 
The arrangement of joints and its movements are unique among human beings. Unlike in mammals, humans can stand on two limbs leaving the upper limbs free for specific uses. Balancing on two limbs, with an ability to stand erect, walk, run and jump with 100 percent precision is a marvel in the creation of human beings.
 
Every human being, male, female or a child has four types of joints. They include Ball & Socket joints, Hinge joints, Semi-movable joints and Immovable joints.
 
Ball & Socket Joints: These are found only in the upper and lower limbs in the shape of shoulder and hip joints respectively. Both the shoulder and hip joints fall into the Ball & Socket type. In this type the ball like structure of the shaft of the long bone fits into a socket type of a structure in the bone adjacent to it facilitating rotation in any angle to any range.
 
One can move the arm around the shoulder joint up and down up to 180 degrees and also rotate the entire upper limb to a full circle. 
 
All these movements are made possible with the head turning and rotating over the socket. Flexible ligaments hold the ball and the socket together so that the head doesn’t come down during movements.  In the shoulder joint the ball is a part of the arm bone called the humerus, which is called the head of the humerus. 
 
The scapula or the shoulder blade found on either side of the back forms the socket for the head to form the shoulder joint. Movements over these joints are performed when the muscles attached to these bones contract or relax as the case may be.
 
Similar is the case with the hip joints where the head of the thighbone called the femur fits into the cavity in the pelvis called acetabulum. Like the upper limb the lower limb can be moved backwards, frontwards and side ways. However the inward movement of the lower limb is very much limited due to the presence of the other limb.
 
Hinge Joints: These joints are found in the elbow and the knees and are known as diarthrosis joints. As the name implies the forearm can move only in one direction like in the case of a door, which can move only in one direction. Similar is the case where the leg can be moved backwards only in one direction and we cannot move it frontward beyond a straight line. In some congenital deformities one can move the forearm or leg beyond the limits  due to hyperextension of the joints.
 
Semi-movable Joints: These joints have a limited mobility and are called amphiarthrosis. The best example is the backbone, which consists of several pieces of bones called vertebrae one above the other. We can perform limited movements both sideways, front and back.

Gymnasts are those who flex these joints to a greater range, with a lot of practice. Because of several vertebrae, which form the backbone, there are many semi-movable joints in the vertebral column or the backbone. Between each vertebra is a cartilage called the disk which might get  prolapsed due to injury or over use of the joint.
 
Immovable Joints: As the name implies we cannot move these joints and are also known as synarthrosis joints.  The best example of immovable joints is the skull, which consists of eight flat and semicircular bones each joining with the other with the help of serrations at the edge of each bone. The joints never give way unless the force on the head is sufficient enough to cause fracture of  skull bones. In infants after birth there are two gaps at the front and back where several skull bones join.

These gaps

are filled up as the child grows and the fully formed skull is a strong cage to protect the brain. Other examples are the flat bones in the pelvis and the sacrum, which cannot be moved due to the fusion of separate bones into one piece.
 

Joints help in the articulation or movement of the joint and therefore it is also known as articulations. They connect the bones, cartilage and the teeth to one another. Every joint has a special shape and structural component that help in controlling the motion range of the parts that it is connected to.

Joints are structurally classified based on the material it is composed of, such as:

  • Fibrous Joints: These joints are made of dense connective tissue made of tough collagen fibers and are immovable. They do not have joint cavity. The skull bones are connected by fibrous joints, eg. the sutures in between the skull bones and the syndesmosis joint of the forearm that holds the radius and ulna bones together.
     
  • Cartilaginous Joints: these bind the bones together with a band of cartilage such as the intervertebral disks of the spine and the joints between the ribs. These allow more movement between the joints than the fibrous joints but lesser movement than the highly movable synovial joints. The connections between are held together by the hyaline cartilage or the fibrocartilage.
     
  • Synovial Joints: This is the most common type of joint and most evolved and therefore is highly movable. It has a fluid-filled space between smooth cartilage pads at the end of articulating bones. The outer layer of capsule may extend into thick, strong bands called ligaments. Ligaments support the joints and restrict undesired movements and dislocations. Synovial membrane lines the capsule which produces a slimy and oily synovial fluid to lubricate the joint and reduce the wear and tear of the joint and friction between joints.

There are five types of synovial joint – a) the ball and socket joint b) elipsoid joint, c) saddle joint d) hinge joint and e) pivot joint.

 
Bone Conditions: The common conditions affecting the joints are dislocations due to tear or laxity of the ligaments surrounding the joints. In some cases habitual dislocation of the shoulder joints is seen often which needs reduction as and when it occurs or surgical procedures to repair the ligaments.

Inflammatory

conditions affecting the joints big or small include gout; rheumatoid arthritis or osteoarthritis Gonococcal arthritis is a condition affecting the big joints due to sexually transmitted diseases. Congenital malformations of any joint are also not uncommon. Cancer of the joints is also a possibility.
 
Injuries mainly due to accidents lead to accumulation of blood within the joint cavities. If infected there may be pus in the joints.
 
Regular exercising of these joints, keep them active and strong, particularly with advancing age, which otherwise can create a lot of stiffness in the joints, owing to disuse.
 
 
 
 
 
*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.