Question

Why can our elbow not move backward?

Answer 1

Joints are the structural arrangement of tissues that help in joining the bones together. Based on their mobility, joints can be classified into three types.
Immovable or fixed or fibrous joints: No movement is involved in this type of joint.
Slightly movable or cartilaginous joints: Slight movement is allowed here.
Freely movable or synovial joints: This joint is involved in free movement.

Complete answer: Synovial membrane which is composed of secretory epithelial cells is present in a synovial joint. This membrane is involved in the secretion of a thick, sticky fluid called the synovial fluid. Joint lubrication is done by this fluid and provides nourishment to the structures within the joint cavity. The stability of the joint is also maintained by it. Based on the shape and the movements the joints allow, synovial joints are classified into the following six types:
1.Gliding joint: This type of joint allows back and forth and side to side movements. This joint is found between the carpal bones and the tarsal bones.
2.Pivot joint: Movement is only in one plane. Rounded or pointed bone fits into a shallow depression present in another bone. It is present just below the elbow.
3.Ellipsoid joint: It allows movement in two planes and is present between the metacarpals and phalanges of the fingers.
4.Saddle joint: It allows free movement and is present between the carpal and metacarpal of the thumb of the finger.
5.Ball-and-socket joint: It is the most freely movable joint present and shoulder and hip joints fall under this category.
6.Hinge joint: This type of joint is involved in the movement only in one direction. When a spool or reel like the surface of one bone fits into the concave surface of another bone, it is referred to as a hinge joint. It is also known as a monoaxial joint because it has the ability to rotate only along one plane. The elbow and the knee have hinge joints.
Thus, we cannot move our elbows backward.

Note: Some important facts about hinge joints are as follows:
1.Thus, the hinge joint is analogous to a hinged door and only backward and forward movement is permitted.
2.The main difference between the hinge joint and the pivot joint is that the hinge joint rotates along one plane while the pivot joint permits axial rotation.