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JOINTS
LEARNING OBJECTIVE: Recognize joint
classifications and identify joint movements for
the key joints in the body.
Wherever two or more bones meet, a joint is
formed. A joint binds various parts of the skeletal
system together and enables body parts to
move in response to skeletal muscle
contractions.
JOINT CLASSIFICATIONS
Joints are classified according to the amount of
movement they permit (fig. 1-26). Joint classifications
are as follows:
· Immovable. Bones of the skull are an example of an immovable joint.
Immovable joints are characterized by
the bones being in close contact with
each other and little or no movement occurring between
the bones.
· Slightly movable. In slightly movable joints, the bones are held
together by broad flattened disks of
cartilage and ligaments (e.g., vertebrae and symphysis
pubis).
Figure 1-25.-The foot: A. Lateral view of foot; B. Right foot viewed from
above.
· Freely movable. Most joints in the body are freely movable joints. The
joint consists of the joint capsule,
articular cartilage, synovial membrane,
and synovial (joint) cavity (fig. 1-26). There are six
classifications of freely movable joints: ball-in-socket,
condyloid, gliding, hinge, pivot, and saddle
joints (fig. 1-27). These joints
have much more complex structures than
the immovable and slightly movable
joints. The ends of the bones in this type of joint are
covered with a smooth layer of cartilage.
The whole joint is enclosed in a
watertight sac or membrane containing a
small amount of lubricating fluid. This
lubrication enables the joint to work with little friction.
Ligaments (cords or sheets of
connective tissue) reach across the
joints from one bone to another and keep the
bone stable. When ligaments are torn, we call the injury
a sprain; when bones are out of place, we
refer to this as a dislocation; and
when bones are chipped or broken, the
injury is called a fracture.
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