Synovial joint is the movable joint in body of mammals. These achieve the movement of the articulating bones at point of contact. Synovial joints are also called “

diarthrosis

”. Functional and structural differences distinguish these joints from fibrous joints (gomphoses, syndesmoses and sutures) and cartilaginous joints (symphyses and synchondroses).

The most important structural difference between the fibrous and synovial joints is the presence of capsules that surround the articulating surface of the synovial joint and existence of lubricating synovial fluid in the capsule.

STRUCTURE OF SYNOVIAL JOINT:

• Articular Capsule:

  Fibrous capsule is continuous with membrane which lines the bones outer surface. Also, it is highly innervated, but also avascular, that is it lacks lymph and blood vessels.

• Synovial Membrane:

  This is the inner most layer of fibrous articular capsule. This covers the synovial cavity lining where articular cartilage is not present.

• Articular cartilage:

  This provides the unloading and loading mechanism to resist shock and load.

TYPES OF SYNOVIAL JOINTS:

Six different types of synovial joints are present in the human body. They include:

1. Gliding Joints:

   These joints have the simplistic range of motion. These allow side to side and back and forth movements.

   For example:

   Vertebrae. Gliding joints allows spine to lean or bend to sides. Adjoining bones of gliding joints are flat, but can have slight concave, curved or convex appearance.

2. Hinges Joints:

   These give back and forth movement and allows the body parts to flex and extend. Particularly, with this joint one bone should be concave and other convex that allows the extensive range of movement.

   For example:

   Knee. Knee joint allows shin and foot to swing outwards and inwards. These movements are helpful in walking, swimming and running.

3. Pivot Joints:

   These are limited to circular movements only. This is composed of depressed and other cone shaped bones which permits to rotate or twist.

   For example:

   Ulna and radius. These are present in the forearm. These permit forearm to turn and provides the necessary supination and pronation.

4. Condyloid Joints:

   These are similar to gliding joints. These also permit side to side and up and down motion. These have concave and oval shaped bones. These are also called “
   

   bi-axial joints

   ”, that is they contain two separate axes.

   For example:

   Radio-carpal joint of wrist.

5. Saddle Joints:

   These are similar to condyloid joints. They contain a convex and concave bones that fit firmly together. These provide wide range of motion.

   For example:

   Carpometacarpal joint of thumb. This permits thumb to be opposable, additionally provides motions which other fingers does not have.

6. Socket and Ball Joints:

   These provide wide range of motion. These contain one convex or round bone which fits into cupped hole or depression in other bone.

   For example:

   Shoulder joint.