Graphics Reference
In-Depth Information
the more stable they are, the less flexible they are. The differences in the
structure of the joints can be attributed to the different roles that each joint
plays within the skeleton. The shoulder and hip joints are the most flexible
and are of the ball-and-socket type. The shoulder joint has a shallower
coupling than the hip joint and provides a greater degree of flexibility.
However, the hip joint is less prone to displacement. The role of the hip is to
be load bearing; the shoulder's function is to provide flexibility in order to
enable manipulation such as lifting. Stability in this case comes at the expense
of flexibility.
A number of different types of joints in the skeleton allow for various levels of
articulation and movement:
• Plane joint
• Hinge joint
• Pivot joint
• Condyloid joint
•
Saddle joint
•
Ball-and-socket joint
Plane Joint
Plane joints are quite irregular in shape though usually flat or slightly curved;
they only allow movement of a sliding action. These joints are to be found
between the carpal bones in the hand.
Hinge Joint
Hinge joints allow movement in one plane around a single axis. The
joint found at the elbow is a hinge joint. This type of joint only allows for
movement along a single axis. This is known as a
uniaxial
joint.
Pivot Joint
Pivot joints allow bones to roll around one another in a rotation movement,
as can be found in the radius and the ulna. A pivot joint is also a uniaxial
joint.
Condyloid Joint
Condyloid joints are oval or egg shaped and fit into a concave shape. These
joints allow movement through two axes: forward and backward and from
side to side. Such a joint is found at the junction between the metacarpal and
phalangeal bones.
Saddle Joint
Saddle joints are a modification of the condyloid joint and allow for more
freedom of movement. They are another example of a biaxial joint. A saddle
joint is located in the thumb.
