12:Types of Synovial Joints? Why is the knee not a pure hinge joint?
Synovial joints are the most common and functionally complex joints in the human body. They are characterized by the presence of a synovial cavity, synovial fluid, and articular cartilage. The types of synovial joints include:
a. Hinge Joint: A hinge joint allows movement in one plane, like a door hinge. Examples include the elbow and knee joints. However, the knee joint is not a pure hinge joint due to its ability to allow slight rotation and limited sideways movement.
b. Gliding Joint: A gliding joint allows bones to glide or slide over one another. These joints facilitate smooth movements in multiple directions. Examples include the joints between the vertebrae in the spine and the small bones in the wrist and ankle.
c. Pivot Joint: A pivot joint allows rotational movement around a central axis. It enables the rotation of one bone around another. The joint between the atlas (C1 vertebra) and the axis (C2 vertebra) in the neck is an example of a pivot joint.
d. Ball and Socket Joint: A ball and socket joint provides the greatest range of motion among all joints. It consists of a rounded ball-shaped end of one bone fitting into a cup-like socket of another bone. The hip and shoulder joints are classic examples of ball and socket joints.
e. Condyloid Joint: A condyloid joint allows movement in two planes, typically flexion/extension and abduction/adduction. The joint at the base of the index finger, where it connects to the metacarpal bone, is an example of a condyloid joint.
f. Saddle Joint: A saddle joint allows movement in two planes, similar to a condyloid joint. It provides enhanced flexibility and stability. The joint between the thumb and the wrist is a saddle joint.
